diff --git a/apriltag/src/main/native/cpp/AprilTag.cpp b/apriltag/src/main/native/cpp/AprilTag.cpp
index adcbe68fb5..a14d9784a8 100644
--- a/apriltag/src/main/native/cpp/AprilTag.cpp
+++ b/apriltag/src/main/native/cpp/AprilTag.cpp
@@ -52,10 +52,10 @@ bool AprilTag::Generate16h5AprilTagImage(wpi::util::RawFrame* frame, int id) {
 }
 
 void wpi::apriltag::to_json(wpi::util::json& json, const AprilTag& apriltag) {
-  json = wpi::util::json{{"ID", apriltag.ID}, {"pose", apriltag.pose}};
+  json = wpi::util::json::object("ID", apriltag.ID, "pose", apriltag.pose);
 }
 
 void wpi::apriltag::from_json(const wpi::util::json& json, AprilTag& apriltag) {
-  apriltag.ID = json.at("ID").get<int>();
+  apriltag.ID = json.at("ID").get_int();
   apriltag.pose = json.at("pose").get<wpi::math::Pose3d>();
 }
diff --git a/apriltag/src/main/native/cpp/AprilTagFieldLayout.cpp b/apriltag/src/main/native/cpp/AprilTagFieldLayout.cpp
index 166ab3b883..567ebe6bdd 100644
--- a/apriltag/src/main/native/cpp/AprilTagFieldLayout.cpp
+++ b/apriltag/src/main/native/cpp/AprilTagFieldLayout.cpp
@@ -22,16 +22,16 @@ AprilTagFieldLayout::AprilTagFieldLayout(std::string_view path) {
     throw std::runtime_error(fmt::format("Cannot open file: {}", path));
   }
 
-  wpi::util::json json =
-      wpi::util::json::parse(fileBuffer.value()->GetCharBuffer());
+  auto buf = fileBuffer.value()->GetCharBuffer();
+  auto json = wpi::util::json::parse_or_throw({buf.data(), buf.size()});
 
-  for (const auto& tag : json.at("tags").get<std::vector<AprilTag>>()) {
+  for (auto&& jtag : json.at("tags").get_array()) {
+    auto tag = jtag.get<AprilTag>();
     m_apriltags[tag.ID] = tag;
   }
-  m_fieldWidth =
-      wpi::units::meter_t{json.at("field").at("width").get<double>()};
+  m_fieldWidth = wpi::units::meter_t{json.at("field").at("width").get_number()};
   m_fieldLength =
-      wpi::units::meter_t{json.at("field").at("length").get<double>()};
+      wpi::units::meter_t{json.at("field").at("length").get_number()};
 }
 
 AprilTagFieldLayout::AprilTagFieldLayout(std::vector<AprilTag> apriltags,
@@ -113,23 +113,24 @@ void wpi::apriltag::to_json(wpi::util::json& json,
     tagVector.push_back(pair.second);
   }
 
-  json = wpi::util::json{{"field",
-                          {{"length", layout.m_fieldLength.value()},
-                           {"width", layout.m_fieldWidth.value()}}},
-                         {"tags", tagVector}};
+  auto field = wpi::util::json::object("length", layout.m_fieldLength.value(),
+                                       "width", layout.m_fieldWidth.value());
+  json = wpi::util::json::object("field", std::move(field), "tags",
+                                 std::move(tagVector));
 }
 
 void wpi::apriltag::from_json(const wpi::util::json& json,
                               AprilTagFieldLayout& layout) {
   layout.m_apriltags.clear();
-  for (const auto& tag : json.at("tags").get<std::vector<AprilTag>>()) {
+  for (auto&& jtag : json.at("tags").get_array()) {
+    auto tag = jtag.get<AprilTag>();
     layout.m_apriltags[tag.ID] = tag;
   }
 
   layout.m_fieldLength =
-      wpi::units::meter_t{json.at("field").at("length").get<double>()};
+      wpi::units::meter_t{json.at("field").at("length").get_number()};
   layout.m_fieldWidth =
-      wpi::units::meter_t{json.at("field").at("width").get<double>()};
+      wpi::units::meter_t{json.at("field").at("width").get_number()};
 }
 
 // Use namespace declaration for forward declaration
@@ -174,6 +175,6 @@ AprilTagFieldLayout AprilTagFieldLayout::LoadField(AprilTagField field) {
       throw std::invalid_argument("Invalid Field");
   }
 
-  wpi::util::json json = wpi::util::json::parse(fieldString);
+  wpi::util::json json = wpi::util::json::parse_or_throw(fieldString);
   return json.get<AprilTagFieldLayout>();
 }
diff --git a/apriltag/src/main/native/include/wpi/apriltag/AprilTag.hpp b/apriltag/src/main/native/include/wpi/apriltag/AprilTag.hpp
index 87384cef07..3ad4fa406b 100644
--- a/apriltag/src/main/native/include/wpi/apriltag/AprilTag.hpp
+++ b/apriltag/src/main/native/include/wpi/apriltag/AprilTag.hpp
@@ -7,7 +7,10 @@
 #include "wpi/math/geometry/Pose3d.hpp"
 #include "wpi/util/RawFrame.hpp"
 #include "wpi/util/SymbolExports.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::apriltag {
 
diff --git a/apriltag/src/main/native/include/wpi/apriltag/AprilTagFieldLayout.hpp b/apriltag/src/main/native/include/wpi/apriltag/AprilTagFieldLayout.hpp
index 4b6548f26c..810cc63cc8 100644
--- a/apriltag/src/main/native/include/wpi/apriltag/AprilTagFieldLayout.hpp
+++ b/apriltag/src/main/native/include/wpi/apriltag/AprilTagFieldLayout.hpp
@@ -14,7 +14,10 @@
 #include "wpi/math/geometry/Pose3d.hpp"
 #include "wpi/units/length.hpp"
 #include "wpi/util/SymbolExports.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::apriltag {
 /**
diff --git a/cameraserver/multiCameraServer/src/main/native/cpp/main.cpp b/cameraserver/multiCameraServer/src/main/native/cpp/main.cpp
index d37982a819..1018fc0007 100644
--- a/cameraserver/multiCameraServer/src/main/native/cpp/main.cpp
+++ b/cameraserver/multiCameraServer/src/main/native/cpp/main.cpp
@@ -69,8 +69,8 @@ bool ReadCameraConfig(const wpi::util::json& config) {
 
   // name
   try {
-    c.name = config.at("name").get<std::string>();
-  } catch (const wpi::util::json::exception& e) {
+    c.name = config.at("name").get_string();
+  } catch (const std::logic_error& e) {
     wpi::util::print(stderr,
                      "config error in '{}': could not read camera name: {}\n",
                      configFile, e.what());
@@ -79,8 +79,8 @@ bool ReadCameraConfig(const wpi::util::json& config) {
 
   // path
   try {
-    c.path = config.at("path").get<std::string>();
-  } catch (const wpi::util::json::exception& e) {
+    c.path = config.at("path").get_string();
+  } catch (const std::logic_error& e) {
     wpi::util::print(
         stderr, "config error in '{}': camera '{}': could not read path: {}\n",
         configFile, c.name, e.what());
@@ -103,17 +103,16 @@ bool ReadConfig() {
   }
 
   // parse file
-  wpi::util::json j;
-  try {
-    j = wpi::util::json::parse(fileBuffer.value()->GetCharBuffer());
-  } catch (const wpi::util::json::parse_error& e) {
-    wpi::util::print(stderr, "config error in '{}': byte {}: {}\n", configFile,
-                     e.byte, e.what());
+  auto buf = fileBuffer.value()->GetCharBuffer();
+  auto j = wpi::util::json::parse({buf.data(), buf.size()});
+  if (!j) {
+    wpi::util::print(stderr, "config error in '{}': {}\n", configFile,
+                     j.error());
     return false;
   }
 
   // top level must be an object
-  if (!j.is_object()) {
+  if (!j->is_object()) {
     wpi::util::print(stderr, "config error in '{}': must be JSON object\n",
                      configFile);
     return false;
@@ -121,8 +120,8 @@ bool ReadConfig() {
 
   // team number
   try {
-    team = j.at("team").get<unsigned int>();
-  } catch (const wpi::util::json::exception& e) {
+    team = j->at("team").get_int();
+  } catch (const std::logic_error& e) {
     wpi::util::print(stderr,
                      "config error in '{}': could not read team number: {}\n",
                      configFile, e.what());
@@ -130,9 +129,9 @@ bool ReadConfig() {
   }
 
   // ntmode (optional)
-  if (j.count("ntmode") != 0) {
+  if (auto ntmode = j->lookup("ntmode")) {
     try {
-      auto str = j.at("ntmode").get<std::string>();
+      auto str = ntmode->get_string();
       if (wpi::util::equals_lower(str, "client")) {
         server = false;
       } else if (wpi::util::equals_lower(str, "server")) {
@@ -143,7 +142,7 @@ bool ReadConfig() {
             "config error in '{}': could not understand ntmode value '{}'\n",
             configFile, str);
       }
-    } catch (const wpi::util::json::exception& e) {
+    } catch (const std::logic_error& e) {
       wpi::util::print(stderr,
                        "config error in '{}': could not read ntmode: {}\n",
                        configFile, e.what());
@@ -152,12 +151,12 @@ bool ReadConfig() {
 
   // cameras
   try {
-    for (auto&& camera : j.at("cameras")) {
+    for (auto&& camera : j->at("cameras").get_array()) {
       if (!ReadCameraConfig(camera)) {
         return false;
       }
     }
-  } catch (const wpi::util::json::exception& e) {
+  } catch (const std::logic_error& e) {
     wpi::util::print(stderr,
                      "config error in '{}': could not read cameras: {}\n",
                      configFile, e.what());
diff --git a/cscore/src/main/native/cpp/PropertyContainer.cpp b/cscore/src/main/native/cpp/PropertyContainer.cpp
index d57471b8ed..e609c5905e 100644
--- a/cscore/src/main/native/cpp/PropertyContainer.cpp
+++ b/cscore/src/main/native/cpp/PropertyContainer.cpp
@@ -6,6 +6,7 @@
 
 #include <memory>
 #include <string>
+#include <utility>
 #include <vector>
 
 #include "wpi/util/Logger.hpp"
@@ -244,11 +245,11 @@ bool PropertyContainer::SetPropertiesJson(const wpi::util::json& config,
                                           wpi::util::Logger& logger,
                                           std::string_view logName,
                                           CS_Status* status) {
-  for (auto&& prop : config) {
+  for (auto&& prop : config.get_array()) {
     std::string name;
     try {
-      name = prop.at("name").get<std::string>();
-    } catch (const wpi::util::json::exception& e) {
+      name = prop.at("name").get_string();
+    } catch (const std::logic_error& e) {
       WPI_WARNING(logger, "{}: SetConfigJson: could not read property name: {}",
                   logName, e.what());
       continue;
@@ -257,22 +258,22 @@ bool PropertyContainer::SetPropertiesJson(const wpi::util::json& config,
     try {
       auto& v = prop.at("value");
       if (v.is_string()) {
-        std::string val = v.get<std::string>();
+        std::string val = v.get_string();
         WPI_INFO(logger, "{}: SetConfigJson: setting property '{}' to '{}'",
                  logName, name, val);
         SetStringProperty(n, val, status);
-      } else if (v.is_boolean()) {
-        bool val = v.get<bool>();
+      } else if (v.is_bool()) {
+        bool val = v.get_bool();
         WPI_INFO(logger, "{}: SetConfigJson: setting property '{}' to {}",
                  logName, name, val);
         SetProperty(n, val, status);
       } else {
-        int val = v.get<int>();
+        int val = v.get_int();
         WPI_INFO(logger, "{}: SetConfigJson: setting property '{}' to {}",
                  logName, name, val);
         SetProperty(n, val, status);
       }
-    } catch (const wpi::util::json::exception& e) {
+    } catch (const std::logic_error& e) {
       WPI_WARNING(logger,
                   "{}: SetConfigJson: could not read property value: {}",
                   logName, e.what());
@@ -289,22 +290,22 @@ wpi::util::json PropertyContainer::GetPropertiesJsonObject(CS_Status* status) {
   for (int p : EnumerateProperties(propVec, status)) {
     wpi::util::json prop;
     wpi::util::SmallString<128> strBuf;
-    prop.emplace("name", GetPropertyName(p, strBuf, status));
+    prop["name"] = GetPropertyName(p, strBuf, status);
     switch (GetPropertyKind(p)) {
       case CS_PROP_BOOLEAN:
-        prop.emplace("value", static_cast<bool>(GetProperty(p, status)));
+        prop["value"] = static_cast<bool>(GetProperty(p, status));
         break;
       case CS_PROP_INTEGER:
       case CS_PROP_ENUM:
-        prop.emplace("value", GetProperty(p, status));
+        prop["value"] = GetProperty(p, status);
         break;
       case CS_PROP_STRING:
-        prop.emplace("value", GetStringProperty(p, strBuf, status));
+        prop["value"] = GetStringProperty(p, strBuf, status);
         break;
       default:
         continue;
     }
-    j.emplace_back(prop);
+    j.emplace_back(std::move(prop));
   }
 
   return j;
diff --git a/cscore/src/main/native/cpp/PropertyContainer.hpp b/cscore/src/main/native/cpp/PropertyContainer.hpp
index 2461d44548..e142f94f06 100644
--- a/cscore/src/main/native/cpp/PropertyContainer.hpp
+++ b/cscore/src/main/native/cpp/PropertyContainer.hpp
@@ -15,13 +15,13 @@
 #include "PropertyImpl.hpp"
 #include "wpi/cs/cscore_c.h"
 #include "wpi/util/StringMap.hpp"
-#include "wpi/util/json_fwd.hpp"
 #include "wpi/util/mutex.hpp"
 
 namespace wpi::util {
 class Logger;
 template <typename T>
 class SmallVectorImpl;
+class json;
 }  // namespace wpi::util
 
 namespace wpi::cs {
diff --git a/cscore/src/main/native/cpp/SinkImpl.cpp b/cscore/src/main/native/cpp/SinkImpl.cpp
index 81be1818ae..e1e8a01cfc 100644
--- a/cscore/src/main/native/cpp/SinkImpl.cpp
+++ b/cscore/src/main/native/cpp/SinkImpl.cpp
@@ -5,6 +5,7 @@
 #include "SinkImpl.hpp"
 
 #include <string>
+#include <utility>
 
 #include "Instance.hpp"
 #include "Notifier.hpp"
@@ -128,20 +129,18 @@ std::string_view SinkImpl::GetError(
 }
 
 bool SinkImpl::SetConfigJson(std::string_view config, CS_Status* status) {
-  wpi::util::json j;
-  try {
-    j = wpi::util::json::parse(config);
-  } catch (const wpi::util::json::parse_error& e) {
-    SWARNING("SetConfigJson: parse error at byte {}: {}", e.byte, e.what());
+  auto j = wpi::util::json::parse(config);
+  if (!j) {
+    SWARNING("SetConfigJson: parse error: {}", j.error());
     *status = CS_PROPERTY_WRITE_FAILED;
     return false;
   }
-  return SetConfigJson(j, status);
+  return SetConfigJson(*j, status);
 }
 
 bool SinkImpl::SetConfigJson(const wpi::util::json& config, CS_Status* status) {
-  if (config.count("properties") != 0) {
-    SetPropertiesJson(config.at("properties"), m_logger, GetName(), status);
+  if (auto properties = config.lookup("properties")) {
+    SetPropertiesJson(*properties, m_logger, GetName(), status);
   }
 
   return true;
@@ -150,7 +149,7 @@ bool SinkImpl::SetConfigJson(const wpi::util::json& config, CS_Status* status) {
 std::string SinkImpl::GetConfigJson(CS_Status* status) {
   std::string rv;
   wpi::util::raw_string_ostream os(rv);
-  GetConfigJsonObject(status).dump(os, 4);
+  GetConfigJsonObject(status).marshal(os, true, 4);
   os.flush();
   return rv;
 }
@@ -160,7 +159,7 @@ wpi::util::json SinkImpl::GetConfigJsonObject(CS_Status* status) {
 
   wpi::util::json props = GetPropertiesJsonObject(status);
   if (props.is_array()) {
-    j.emplace("properties", props);
+    j["properties"] = std::move(props);
   }
 
   return j;
diff --git a/cscore/src/main/native/cpp/SinkImpl.hpp b/cscore/src/main/native/cpp/SinkImpl.hpp
index 865420a1cd..ef35d5aa03 100644
--- a/cscore/src/main/native/cpp/SinkImpl.hpp
+++ b/cscore/src/main/native/cpp/SinkImpl.hpp
@@ -10,7 +10,10 @@
 
 #include "SourceImpl.hpp"
 #include "wpi/util/Logger.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::cs {
 
diff --git a/cscore/src/main/native/cpp/SourceImpl.cpp b/cscore/src/main/native/cpp/SourceImpl.cpp
index 4d5df1565e..f1e9909aad 100644
--- a/cscore/src/main/native/cpp/SourceImpl.cpp
+++ b/cscore/src/main/native/cpp/SourceImpl.cpp
@@ -180,15 +180,13 @@ bool SourceImpl::SetFPS(int fps, CS_Status* status) {
 }
 
 bool SourceImpl::SetConfigJson(std::string_view config, CS_Status* status) {
-  wpi::util::json j;
-  try {
-    j = wpi::util::json::parse(config);
-  } catch (const wpi::util::json::parse_error& e) {
-    SWARNING("SetConfigJson: parse error at byte {}: {}", e.byte, e.what());
+  auto j = wpi::util::json::parse(config);
+  if (!j) {
+    SWARNING("SetConfigJson: parse error: {}", j.error());
     *status = CS_PROPERTY_WRITE_FAILED;
     return false;
   }
-  return SetConfigJson(j, status);
+  return SetConfigJson(*j, status);
 }
 
 bool SourceImpl::SetConfigJson(const wpi::util::json& config,
@@ -196,9 +194,9 @@ bool SourceImpl::SetConfigJson(const wpi::util::json& config,
   VideoMode mode;
 
   // pixel format
-  if (config.count("pixel format") != 0) {
+  if (auto pixelFormat = config.lookup("pixel format")) {
     try {
-      auto str = config.at("pixel format").get<std::string>();
+      auto str = pixelFormat->get_string();
       if (wpi::util::equals_lower(str, "mjpeg")) {
         mode.pixelFormat = wpi::util::PixelFormat::MJPEG;
       } else if (wpi::util::equals_lower(str, "yuyv")) {
@@ -219,34 +217,34 @@ bool SourceImpl::SetConfigJson(const wpi::util::json& config,
         SWARNING("SetConfigJson: could not understand pixel format value '{}'",
                  str);
       }
-    } catch (const wpi::util::json::exception& e) {
+    } catch (const std::logic_error& e) {
       SWARNING("SetConfigJson: could not read pixel format: {}", e.what());
     }
   }
 
   // width
-  if (config.count("width") != 0) {
+  if (auto width = config.lookup("width")) {
     try {
-      mode.width = config.at("width").get<unsigned int>();
-    } catch (const wpi::util::json::exception& e) {
+      mode.width = width->get_int();
+    } catch (const std::logic_error& e) {
       SWARNING("SetConfigJson: could not read width: {}", e.what());
     }
   }
 
   // height
-  if (config.count("height") != 0) {
+  if (auto height = config.lookup("height")) {
     try {
-      mode.height = config.at("height").get<unsigned int>();
-    } catch (const wpi::util::json::exception& e) {
+      mode.height = height->get_int();
+    } catch (const std::logic_error& e) {
       SWARNING("SetConfigJson: could not read height: {}", e.what());
     }
   }
 
   // fps
-  if (config.count("fps") != 0) {
+  if (auto fps = config.lookup("fps")) {
     try {
-      mode.fps = config.at("fps").get<unsigned int>();
-    } catch (const wpi::util::json::exception& e) {
+      mode.fps = fps->get_int();
+    } catch (const std::logic_error& e) {
       SWARNING("SetConfigJson: could not read fps: {}", e.what());
     }
   }
@@ -277,22 +275,21 @@ bool SourceImpl::SetConfigJson(const wpi::util::json& config,
   }
 
   // brightness
-  if (config.count("brightness") != 0) {
+  if (auto brightness = config.lookup("brightness")) {
     try {
-      int val = config.at("brightness").get<int>();
+      int val = brightness->get_int();
       SINFO("SetConfigJson: setting brightness to {}", val);
       SetBrightness(val, status);
-    } catch (const wpi::util::json::exception& e) {
+    } catch (const std::logic_error& e) {
       SWARNING("SetConfigJson: could not read brightness: {}", e.what());
     }
   }
 
   // white balance
-  if (config.count("white balance") != 0) {
+  if (auto whiteBalance = config.lookup("white balance")) {
     try {
-      auto& setting = config.at("white balance");
-      if (setting.is_string()) {
-        auto str = setting.get<std::string>();
+      if (whiteBalance->is_string()) {
+        auto str = whiteBalance->get_string();
         if (wpi::util::equals_lower(str, "auto")) {
           SINFO("SetConfigJson: setting white balance to {}", "auto");
           SetWhiteBalanceAuto(status);
@@ -305,21 +302,20 @@ bool SourceImpl::SetConfigJson(const wpi::util::json& config,
               str);
         }
       } else {
-        int val = setting.get<int>();
+        int val = whiteBalance->get_int();
         SINFO("SetConfigJson: setting white balance to {}", val);
         SetWhiteBalanceManual(val, status);
       }
-    } catch (const wpi::util::json::exception& e) {
+    } catch (const std::logic_error& e) {
       SWARNING("SetConfigJson: could not read white balance: {}", e.what());
     }
   }
 
   // exposure
-  if (config.count("exposure") != 0) {
+  if (auto exposure = config.lookup("exposure")) {
     try {
-      auto& setting = config.at("exposure");
-      if (setting.is_string()) {
-        auto str = setting.get<std::string>();
+      if (exposure->is_string()) {
+        auto str = exposure->get_string();
         if (wpi::util::equals_lower(str, "auto")) {
           SINFO("SetConfigJson: setting exposure to {}", "auto");
           SetExposureAuto(status);
@@ -331,18 +327,18 @@ bool SourceImpl::SetConfigJson(const wpi::util::json& config,
                    str);
         }
       } else {
-        int val = setting.get<int>();
+        int val = exposure->get_int();
         SINFO("SetConfigJson: setting exposure to {}", val);
         SetExposureManual(val, status);
       }
-    } catch (const wpi::util::json::exception& e) {
+    } catch (const std::logic_error& e) {
       SWARNING("SetConfigJson: could not read exposure: {}", e.what());
     }
   }
 
   // properties
-  if (config.count("properties") != 0) {
-    SetPropertiesJson(config.at("properties"), m_logger, GetName(), status);
+  if (auto properties = config.lookup("properties")) {
+    SetPropertiesJson(*properties, m_logger, GetName(), status);
   }
 
   return true;
@@ -351,8 +347,7 @@ bool SourceImpl::SetConfigJson(const wpi::util::json& config,
 std::string SourceImpl::GetConfigJson(CS_Status* status) {
   std::string rv;
   wpi::util::raw_string_ostream os(rv);
-  GetConfigJsonObject(status).dump(os, 4);
-  os.flush();
+  GetConfigJsonObject(status).marshal(os, true, 4);
   return rv;
 }
 
@@ -390,22 +385,22 @@ wpi::util::json SourceImpl::GetConfigJsonObject(CS_Status* status) {
       break;
   }
   if (!pixelFormat.empty()) {
-    j.emplace("pixel format", pixelFormat);
+    j["pixel format"] = pixelFormat;
   }
 
   // width
   if (m_mode.width != 0) {
-    j.emplace("width", m_mode.width);
+    j["width"] = m_mode.width;
   }
 
   // height
   if (m_mode.height != 0) {
-    j.emplace("height", m_mode.height);
+    j["height"] = m_mode.height;
   }
 
   // fps
   if (m_mode.fps != 0) {
-    j.emplace("fps", m_mode.fps);
+    j["fps"] = m_mode.fps;
   }
 
   // TODO: output brightness, white balance, and exposure?
@@ -413,7 +408,7 @@ wpi::util::json SourceImpl::GetConfigJsonObject(CS_Status* status) {
   // properties
   wpi::util::json props = GetPropertiesJsonObject(status);
   if (props.is_array()) {
-    j.emplace("properties", props);
+    j["properties"] = std::move(props);
   }
 
   return j;
diff --git a/cscore/src/main/native/cpp/SourceImpl.hpp b/cscore/src/main/native/cpp/SourceImpl.hpp
index 13e548390a..e441db2972 100644
--- a/cscore/src/main/native/cpp/SourceImpl.hpp
+++ b/cscore/src/main/native/cpp/SourceImpl.hpp
@@ -20,9 +20,12 @@
 #include "wpi/util/PixelFormat.hpp"
 #include "wpi/util/RawFrame.h"
 #include "wpi/util/condition_variable.hpp"
-#include "wpi/util/json_fwd.hpp"
 #include "wpi/util/mutex.hpp"
 
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
+
 namespace wpi::cs {
 
 class Notifier;
diff --git a/cscore/src/main/native/include/wpi/cs/VideoSink.hpp b/cscore/src/main/native/include/wpi/cs/VideoSink.hpp
index 93a2b1e8e3..98eeaf57d4 100644
--- a/cscore/src/main/native/include/wpi/cs/VideoSink.hpp
+++ b/cscore/src/main/native/include/wpi/cs/VideoSink.hpp
@@ -12,7 +12,10 @@
 #include "wpi/cs/VideoProperty.hpp"
 #include "wpi/cs/VideoSource.hpp"
 #include "wpi/cs/cscore_cpp.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::cs {
 
diff --git a/cscore/src/main/native/include/wpi/cs/cscore_cpp.hpp b/cscore/src/main/native/include/wpi/cs/cscore_cpp.hpp
index d581ea2857..7d206068de 100644
--- a/cscore/src/main/native/include/wpi/cs/cscore_cpp.hpp
+++ b/cscore/src/main/native/include/wpi/cs/cscore_cpp.hpp
@@ -18,7 +18,6 @@
 #include "wpi/cs/cscore_c.h"
 #include "wpi/util/PixelFormat.hpp"
 #include "wpi/util/SmallVector.hpp"
-#include "wpi/util/json_fwd.hpp"
 
 #ifdef _WIN32
 // Disable uninitialized variable warnings
@@ -26,6 +25,10 @@
 #pragma warning(disable : 26495)
 #endif
 
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
+
 /** CameraServer (cscore) namespace */
 namespace wpi::cs {
 
diff --git a/glass/src/lib/native/cpp/Context.cpp b/glass/src/lib/native/cpp/Context.cpp
index 3988577f16..7b7cbd7599 100644
--- a/glass/src/lib/native/cpp/Context.cpp
+++ b/glass/src/lib/native/cpp/Context.cpp
@@ -67,63 +67,55 @@ static bool JsonToWindow(const wpi::util::json& jfile, const char* filename) {
   std::string iniStr;
   wpi::util::raw_string_ostream ini{iniStr};
 
-  for (auto&& jsection : jfile.items()) {
-    if (jsection.key() == "Docking") {
+  for (auto&& [sect_key, sect_value] : jfile.get_object()) {
+    if (sect_key == "Docking") {
       continue;
     }
-    if (!jsection.value().is_object()) {
-      ImGui::LogText("%s section %s is not object", filename,
-                     jsection.key().c_str());
+    if (!sect_value.is_object()) {
+      ImGui::LogText("%s section %s is not object", filename, sect_key.c_str());
       return false;
     }
-    for (auto&& jsubsection : jsection.value().items()) {
-      if (!jsubsection.value().is_object()) {
+    for (auto&& [sub_key, sub_value] : sect_value.get_object()) {
+      if (!sub_value.is_object()) {
         ImGui::LogText("%s section %s subsection %s is not object", filename,
-                       jsection.key().c_str(), jsubsection.key().c_str());
+                       sect_key.c_str(), sub_key.c_str());
         return false;
       }
-      ini << '[' << jsection.key() << "][" << jsubsection.key() << "]\n";
-      for (auto&& jkv : jsubsection.value().items()) {
-        try {
-          auto& value = jkv.value().get_ref<const std::string&>();
-          ini << jkv.key() << '=' << value << "\n";
-        } catch (wpi::util::json::exception&) {
+      ini << '[' << sect_key << "][" << sub_key << "]\n";
+      for (auto&& [key, value] : sub_value.get_object()) {
+        if (!value.is_string()) {
           ImGui::LogText("%s section %s subsection %s value %s is not string",
-                         filename, jsection.key().c_str(),
-                         jsubsection.key().c_str(), jkv.key().c_str());
+                         filename, sect_key.c_str(), sub_key.c_str(),
+                         key.c_str());
           return false;
         }
+        ini << key << '=' << value.get_string() << "\n";
       }
       ini << '\n';
     }
   }
 
   // emit Docking section last
-  auto docking = jfile.find("Docking");
-  if (docking != jfile.end()) {
-    for (auto&& jsubsection : docking->items()) {
-      if (!jsubsection.value().is_array()) {
+  if (auto docking = jfile.lookup("Docking")) {
+    for (auto&& [sub_key, sub_value] : docking->get_object()) {
+      if (!sub_value.is_array()) {
         ImGui::LogText("%s section %s subsection %s is not array", filename,
-                       "Docking", jsubsection.key().c_str());
+                       "Docking", sub_key.c_str());
         return false;
       }
-      ini << "[Docking][" << jsubsection.key() << "]\n";
-      for (auto&& jv : jsubsection.value()) {
-        try {
-          auto& value = jv.get_ref<const std::string&>();
-          ini << value << "\n";
-        } catch (wpi::util::json::exception&) {
+      ini << "[Docking][" << sub_key << "]\n";
+      for (auto&& value : sub_value.get_array()) {
+        if (!value.is_string()) {
           ImGui::LogText("%s section %s subsection %s value is not string",
-                         filename, "Docking", jsubsection.key().c_str());
+                         filename, "Docking", sub_key.c_str());
           return false;
         }
+        ini << value.get_string() << "\n";
       }
       ini << '\n';
     }
   }
 
-  ini.flush();
-
   ImGui::LoadIniSettingsFromMemory(iniStr.data(), iniStr.size());
   return true;
 }
@@ -135,12 +127,12 @@ static bool LoadWindowStorageImpl(const std::string& filename) {
                    fileBuffer.error().message().c_str());
     return false;
   }
-  try {
-    return JsonToWindow(
-        wpi::util::json::parse(fileBuffer.value()->GetCharBuffer()),
-        filename.c_str());
-  } catch (wpi::util::json::parse_error& e) {
-    ImGui::LogText("Error loading %s: %s", filename.c_str(), e.what());
+  auto buffer = fileBuffer.value()->GetCharBuffer();
+  auto j = wpi::util::json::parse({buffer.data(), buffer.size()});
+  if (j) {
+    return JsonToWindow(*j, filename.c_str());
+  } else {
+    ImGui::LogText("Error loading %s: %s", filename.c_str(), j.error());
     return false;
   }
 }
@@ -154,12 +146,12 @@ static bool LoadStorageRootImpl(Context* ctx, const std::string& filename,
     return false;
   }
   auto [it, createdStorage] = ctx->storageRoots.try_emplace(rootName);
-  try {
-    it->second.FromJson(
-        wpi::util::json::parse(fileBuffer.value()->GetCharBuffer()),
-        filename.c_str());
-  } catch (wpi::util::json::parse_error& e) {
-    ImGui::LogText("Error loading %s: %s", filename.c_str(), e.what());
+  auto buffer = fileBuffer.value()->GetCharBuffer();
+  auto j = wpi::util::json::parse({buffer.data(), buffer.size()});
+  if (j) {
+    it->second.FromJson(*j, filename.c_str());
+  } else {
+    ImGui::LogText("Error loading %s: %s", filename.c_str(), j.error());
     if (createdStorage) {
       ctx->storageRoots.erase(it);
     }
@@ -257,7 +249,7 @@ bool SaveWindowStorageImpl(const std::string& filename) {
                    ec.message().c_str());
     return false;
   }
-  WindowToJson().dump(os, 2);
+  WindowToJson().marshal(os, true, 2);
   os << '\n';
   return true;
 }
@@ -271,7 +263,7 @@ static bool SaveStorageRootImpl(Context* ctx, const std::string& filename,
                    ec.message().c_str());
     return false;
   }
-  storage.ToJson().dump(os, 2);
+  storage.ToJson().marshal(os, true, 2);
   os << '\n';
   return true;
 }
diff --git a/glass/src/lib/native/cpp/Storage.cpp b/glass/src/lib/native/cpp/Storage.cpp
index a0cb6e8683..0e6257a1be 100644
--- a/glass/src/lib/native/cpp/Storage.cpp
+++ b/glass/src/lib/native/cpp/Storage.cpp
@@ -348,7 +348,7 @@ void Storage::EraseChildren() {
 static bool JsonArrayToStorage(Storage::Value* valuePtr,
                                const wpi::util::json& jarr,
                                const char* filename) {
-  auto& arr = jarr.get_ref<const wpi::util::json::array_t&>();
+  auto& arr = jarr.get_array();
   if (arr.empty()) {
     ImGui::LogText("empty array in %s, ignoring", filename);
     return false;
@@ -356,42 +356,45 @@ static bool JsonArrayToStorage(Storage::Value* valuePtr,
 
   // guess array type from first element
   switch (arr[0].type()) {
-    case wpi::util::json::value_t::boolean:
+    case wpi::util::json::Type::Bool:
       if (valuePtr->type != Storage::Value::kBoolArray) {
         valuePtr->Reset(Storage::Value::kBoolArray);
         valuePtr->boolArray = new std::vector<int>();
         valuePtr->boolArrayDefault = nullptr;
       }
       break;
-    case wpi::util::json::value_t::number_float:
+    case wpi::util::json::Type::Float:
+    case wpi::util::json::Type::Double:
       if (valuePtr->type != Storage::Value::kDoubleArray) {
         valuePtr->Reset(Storage::Value::kDoubleArray);
         valuePtr->doubleArray = new std::vector<double>();
         valuePtr->doubleArrayDefault = nullptr;
       }
       break;
-    case wpi::util::json::value_t::number_integer:
-    case wpi::util::json::value_t::number_unsigned:
+    case wpi::util::json::Type::Int:
       if (valuePtr->type != Storage::Value::kInt64Array) {
         valuePtr->Reset(Storage::Value::kInt64Array);
         valuePtr->int64Array = new std::vector<int64_t>();
         valuePtr->int64ArrayDefault = nullptr;
       }
       break;
-    case wpi::util::json::value_t::string:
+    case wpi::util::json::Type::Uint:
+      ImGui::LogText("too large of integer in %s, ignoring", filename);
+      return false;
+    case wpi::util::json::Type::String:
       if (valuePtr->type != Storage::Value::kStringArray) {
         valuePtr->Reset(Storage::Value::kStringArray);
         valuePtr->stringArray = new std::vector<std::string>();
         valuePtr->stringArrayDefault = nullptr;
       }
       break;
-    case wpi::util::json::value_t::object:
+    case wpi::util::json::Type::Object:
       if (valuePtr->type != Storage::Value::kChildArray) {
         valuePtr->Reset(Storage::Value::kChildArray);
         valuePtr->childArray = new std::vector<std::unique_ptr<Storage>>();
       }
       break;
-    case wpi::util::json::value_t::array:
+    case wpi::util::json::Type::Array:
       ImGui::LogText("nested array in %s, ignoring", filename);
       return false;
     default:
@@ -402,47 +405,47 @@ static bool JsonArrayToStorage(Storage::Value* valuePtr,
   // loop over array to store elements
   for (auto jvalue : arr) {
     switch (jvalue.type()) {
-      case wpi::util::json::value_t::boolean:
+      case wpi::util::json::Type::Bool:
         if (valuePtr->type == Storage::Value::kBoolArray) {
-          valuePtr->boolArray->push_back(jvalue.get<bool>());
+          valuePtr->boolArray->push_back(jvalue.get_bool());
         } else {
           goto error;
         }
         break;
-      case wpi::util::json::value_t::number_float:
+      case wpi::util::json::Type::Float:
         if (valuePtr->type == Storage::Value::kDoubleArray) {
-          valuePtr->doubleArray->push_back(jvalue.get<double>());
+          valuePtr->doubleArray->push_back(jvalue.get_float());
         } else {
           goto error;
         }
         break;
-      case wpi::util::json::value_t::number_integer:
+      case wpi::util::json::Type::Double:
+        if (valuePtr->type == Storage::Value::kDoubleArray) {
+          valuePtr->doubleArray->push_back(jvalue.get_double());
+        } else {
+          goto error;
+        }
+        break;
+      case wpi::util::json::Type::Int:
         if (valuePtr->type == Storage::Value::kInt64Array) {
-          valuePtr->int64Array->push_back(jvalue.get<int64_t>());
+          valuePtr->int64Array->push_back(jvalue.get_int());
         } else if (valuePtr->type == Storage::Value::kDoubleArray) {
-          valuePtr->doubleArray->push_back(jvalue.get<int64_t>());
+          valuePtr->doubleArray->push_back(jvalue.get_int());
         } else {
           goto error;
         }
         break;
-      case wpi::util::json::value_t::number_unsigned:
-        if (valuePtr->type == Storage::Value::kInt64Array) {
-          valuePtr->int64Array->push_back(jvalue.get<uint64_t>());
-        } else if (valuePtr->type == Storage::Value::kDoubleArray) {
-          valuePtr->doubleArray->push_back(jvalue.get<uint64_t>());
-        } else {
-          goto error;
-        }
-        break;
-      case wpi::util::json::value_t::string:
+      case wpi::util::json::Type::Uint:
+        ImGui::LogText("too large of integer in %s, ignoring", filename);
+        return false;
+      case wpi::util::json::Type::String:
         if (valuePtr->type == Storage::Value::kStringArray) {
-          valuePtr->stringArray->emplace_back(
-              jvalue.get_ref<const std::string&>());
+          valuePtr->stringArray->emplace_back(jvalue.get_string());
         } else {
           goto error;
         }
         break;
-      case wpi::util::json::value_t::object:
+      case wpi::util::json::Type::Object:
         if (valuePtr->type == Storage::Value::kChildArray) {
           valuePtr->childArray->emplace_back(std::make_unique<Storage>());
           valuePtr->childArray->back()->FromJson(jvalue, filename);
@@ -450,7 +453,7 @@ static bool JsonArrayToStorage(Storage::Value* valuePtr,
           goto error;
         }
         break;
-      case wpi::util::json::value_t::array:
+      case wpi::util::json::Type::Array:
         ImGui::LogText("nested array in %s, ignoring", filename);
         return false;
       default:
@@ -474,53 +477,52 @@ bool Storage::FromJson(const wpi::util::json& json, const char* filename) {
     ImGui::LogText("non-object in %s", filename);
     return false;
   }
-  for (auto&& jkv : json.items()) {
-    auto& valuePtr = m_values[jkv.key()];
+  for (auto&& [key, jvalue] : json.get_object()) {
+    auto& valuePtr = m_values[key];
     bool created = false;
     if (!valuePtr) {
       valuePtr = std::make_unique<Value>();
       created = true;
     }
-    auto& jvalue = jkv.value();
     switch (jvalue.type()) {
-      case wpi::util::json::value_t::boolean:
+      case wpi::util::json::Type::Bool:
         valuePtr->Reset(Value::kBool);
-        valuePtr->boolVal = jvalue.get<bool>();
+        valuePtr->boolVal = jvalue.get_bool();
         break;
-      case wpi::util::json::value_t::number_float:
+      case wpi::util::json::Type::Float:
         valuePtr->Reset(Value::kDouble);
-        valuePtr->doubleVal = jvalue.get<double>();
+        valuePtr->doubleVal = jvalue.get_float();
         break;
-      case wpi::util::json::value_t::number_integer:
+      case wpi::util::json::Type::Double:
+        valuePtr->Reset(Value::kDouble);
+        valuePtr->doubleVal = jvalue.get_double();
+        break;
+      case wpi::util::json::Type::Int:
         valuePtr->Reset(Value::kInt64);
-        valuePtr->int64Val = jvalue.get<int64_t>();
+        valuePtr->int64Val = jvalue.get_int();
         break;
-      case wpi::util::json::value_t::number_unsigned:
-        valuePtr->Reset(Value::kInt64);
-        valuePtr->int64Val = jvalue.get<uint64_t>();
-        break;
-      case wpi::util::json::value_t::string:
+      case wpi::util::json::Type::String:
         valuePtr->Reset(Value::kString);
-        valuePtr->stringVal = jvalue.get_ref<const std::string&>();
+        valuePtr->stringVal = jvalue.get_string();
         break;
-      case wpi::util::json::value_t::object:
+      case wpi::util::json::Type::Object:
         if (valuePtr->type != Value::kChild) {
           valuePtr->Reset(Value::kChild);
           valuePtr->child = new Storage;
         }
         valuePtr->child->FromJson(jvalue, filename);  // recurse
         break;
-      case wpi::util::json::value_t::array:
+      case wpi::util::json::Type::Array:
         if (!JsonArrayToStorage(valuePtr.get(), jvalue, filename)) {
           if (created) {
-            m_values.erase(jkv.key());
+            m_values.erase(key);
           }
         }
         break;
       default:
         ImGui::LogText("null value in %s, ignoring", filename);
         if (created) {
-          m_values.erase(jkv.key());
+          m_values.erase(key);
         }
         break;
     }
@@ -545,8 +547,9 @@ wpi::util::json StorageToJsonArray<std::unique_ptr<Storage>>(
     jarr.emplace_back(v->ToJson());
   }
   // remove any trailing empty items
-  while (!jarr.empty() && jarr.back().empty()) {
-    jarr.get_ref<wpi::util::json::array_t&>().pop_back();
+  auto& jarrArr = jarr.get_array();
+  while (!jarrArr.empty() && jarrArr.back().empty()) {
+    jarrArr.pop_back();
   }
   return jarr;
 }
@@ -602,7 +605,7 @@ wpi::util::json Storage::ToJson() const {
       default:
         continue;
     }
-    j.emplace(kv.first, std::move(jelem));
+    j[kv.first] = std::move(jelem);
   }
   return j;
 }
diff --git a/glass/src/lib/native/cpp/other/Field2D.cpp b/glass/src/lib/native/cpp/other/Field2D.cpp
index f67577bf69..74d51857d3 100644
--- a/glass/src/lib/native/cpp/other/Field2D.cpp
+++ b/glass/src/lib/native/cpp/other/Field2D.cpp
@@ -451,16 +451,14 @@ void FieldInfo::LoadImage() {
 
 bool FieldInfo::LoadJson(std::span<const char> is, std::string_view filename) {
   // parse file
-  wpi::util::json j;
-  try {
-    j = wpi::util::json::parse(is);
-  } catch (const wpi::util::json::parse_error& e) {
-    wpi::util::print(stderr, "GUI: JSON: could not parse: {}\n", e.what());
+  auto j = wpi::util::json::parse({is.data(), is.size()});
+  if (!j) {
+    wpi::util::print(stderr, "GUI: JSON: could not parse: {}\n", j.error());
     return false;
   }
 
   // top level must be an object
-  if (!j.is_object()) {
+  if (!j->is_object()) {
     std::fputs("GUI: JSON: does not contain a top object\n", stderr);
     return false;
   }
@@ -468,8 +466,8 @@ bool FieldInfo::LoadJson(std::span<const char> is, std::string_view filename) {
   // image filename
   std::string image;
   try {
-    image = j.at("field-image").get<std::string>();
-  } catch (const wpi::util::json::exception& e) {
+    image = j->at("field-image").get_string();
+  } catch (const std::logic_error& e) {
     wpi::util::print(stderr, "GUI: JSON: could not read field-image: {}\n",
                      e.what());
     return false;
@@ -478,11 +476,11 @@ bool FieldInfo::LoadJson(std::span<const char> is, std::string_view filename) {
   // corners
   int top, left, bottom, right;
   try {
-    top = j.at("field-corners").at("top-left").at(1).get<int>();
-    left = j.at("field-corners").at("top-left").at(0).get<int>();
-    bottom = j.at("field-corners").at("bottom-right").at(1).get<int>();
-    right = j.at("field-corners").at("bottom-right").at(0).get<int>();
-  } catch (const wpi::util::json::exception& e) {
+    top = j->at("field-corners").at("top-left").at(1).get_int();
+    left = j->at("field-corners").at("top-left").at(0).get_int();
+    bottom = j->at("field-corners").at("bottom-right").at(1).get_int();
+    right = j->at("field-corners").at("bottom-right").at(0).get_int();
+  } catch (const std::logic_error& e) {
     wpi::util::print(stderr, "GUI: JSON: could not read field-corners: {}\n",
                      e.what());
     return false;
@@ -492,9 +490,9 @@ bool FieldInfo::LoadJson(std::span<const char> is, std::string_view filename) {
   float width;
   float height;
   try {
-    width = j.at("field-size").at(0).get<float>();
-    height = j.at("field-size").at(1).get<float>();
-  } catch (const wpi::util::json::exception& e) {
+    width = j->at("field-size").at(0).get_float();
+    height = j->at("field-size").at(1).get_float();
+  } catch (const std::logic_error& e) {
     wpi::util::print(stderr, "GUI: JSON: could not read field-size: {}\n",
                      e.what());
     return false;
@@ -503,8 +501,8 @@ bool FieldInfo::LoadJson(std::span<const char> is, std::string_view filename) {
   // units for size
   std::string unit;
   try {
-    unit = j.at("field-unit").get<std::string>();
-  } catch (const wpi::util::json::exception& e) {
+    unit = j->at("field-unit").get_string();
+  } catch (const std::logic_error& e) {
     wpi::util::print(stderr, "GUI: JSON: could not read field-unit: {}\n",
                      e.what());
     return false;
diff --git a/glass/src/lib/native/include/wpi/glass/Storage.hpp b/glass/src/lib/native/include/wpi/glass/Storage.hpp
index 9ac50d5e8a..0cf3d5fb6c 100644
--- a/glass/src/lib/native/include/wpi/glass/Storage.hpp
+++ b/glass/src/lib/native/include/wpi/glass/Storage.hpp
@@ -16,7 +16,10 @@
 
 #include "wpi/util/StringMap.hpp"
 #include "wpi/util/iterator_range.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::glass {
 
diff --git a/glass/src/libnt/native/cpp/NTStringChooser.cpp b/glass/src/libnt/native/cpp/NTStringChooser.cpp
index 2308c6327a..c1e536fdf8 100644
--- a/glass/src/libnt/native/cpp/NTStringChooser.cpp
+++ b/glass/src/libnt/native/cpp/NTStringChooser.cpp
@@ -24,7 +24,7 @@ NTStringChooserModel::NTStringChooserModel(wpi::nt::NetworkTableInstance inst,
                      .Subscribe("")},
       m_selectedPub{m_inst.GetStringTopic(fmt::format("{}/selected", path))
                         .PublishEx(wpi::nt::StringTopic::TYPE_STRING,
-                                   {{"retained", true}})},
+                                   wpi::util::json::object("retained", true))},
       m_active{
           m_inst.GetStringTopic(fmt::format("{}/active", path)).Subscribe("")},
       m_options{m_inst.GetStringArrayTopic(fmt::format("{}/options", path))
diff --git a/glass/src/libnt/native/cpp/NetworkTables.cpp b/glass/src/libnt/native/cpp/NetworkTables.cpp
index 07fa47d0f6..ec78b6cea6 100644
--- a/glass/src/libnt/native/cpp/NetworkTables.cpp
+++ b/glass/src/libnt/native/cpp/NetworkTables.cpp
@@ -8,7 +8,6 @@
 #include <cinttypes>
 #include <cstring>
 #include <functional>
-#include <initializer_list>
 #include <map>
 #include <memory>
 #include <span>
@@ -110,18 +109,16 @@ void NetworkTablesModel::Entry::UpdateInfo(wpi::nt::TopicInfo&& info_) {
   properties = info.GetProperties();
 
   persistent = false;
-  auto it = properties.find("persistent");
-  if (it != properties.end()) {
-    if (auto v = it->get_ptr<const bool*>()) {
-      persistent = *v;
+  if (auto prop = properties.lookup("persistent")) {
+    if (prop->is_bool()) {
+      persistent = prop->get_bool();
     }
   }
 
   retained = false;
-  it = properties.find("retained");
-  if (it != properties.end()) {
-    if (auto v = it->get_ptr<const bool*>()) {
-      retained = *v;
+  if (auto prop = properties.lookup("retained")) {
+    if (prop->is_bool()) {
+      retained = prop->get_bool();
     }
   }
 }
@@ -642,7 +639,7 @@ static void UpdateJsonValueSource(NetworkTablesModel& model,
                                   const wpi::util::json& j,
                                   std::string_view name, int64_t time) {
   switch (j.type()) {
-    case wpi::util::json::value_t::object: {
+    case wpi::util::json::Type::Object: {
       if (!out->valueChildrenMap) {
         out->valueChildren.clear();
         out->valueChildrenMap = true;
@@ -652,19 +649,19 @@ static void UpdateJsonValueSource(NetworkTablesModel& model,
         elems[out->valueChildren[i].name] = i;
       }
       bool added = false;
-      for (auto&& kv : j.items()) {
-        auto it = elems.find(kv.key());
+      for (auto&& [key, value] : j.get_object()) {
+        auto it = elems.find(key);
         if (it != elems.end()) {
           auto& child = out->valueChildren[it->second];
-          UpdateJsonValueSource(model, &child, kv.value(), child.path, time);
+          UpdateJsonValueSource(model, &child, value, child.path, time);
           elems.erase(it);
         } else {
           added = true;
           out->valueChildren.emplace_back();
           auto& child = out->valueChildren.back();
-          child.name = kv.key();
+          child.name = key;
           child.path = fmt::format("{}/{}", name, child.name);
-          UpdateJsonValueSource(model, &child, kv.value(), child.path, time);
+          UpdateJsonValueSource(model, &child, value, child.path, time);
         }
       }
       // erase unmatched keys
@@ -680,12 +677,13 @@ static void UpdateJsonValueSource(NetworkTablesModel& model,
       }
       break;
     }
-    case wpi::util::json::value_t::array: {
+    case wpi::util::json::Type::Array: {
+      auto& arr = j.get_array();
       if (out->valueChildrenMap) {
         out->valueChildren.clear();
         out->valueChildrenMap = false;
       }
-      out->valueChildren.resize(j.size());
+      out->valueChildren.resize(arr.size());
       unsigned int i = 0;
       for (auto&& child : out->valueChildren) {
         if (child.name.empty()) {
@@ -693,29 +691,24 @@ static void UpdateJsonValueSource(NetworkTablesModel& model,
           child.path = fmt::format("{}{}", name, child.name);
         }
         // recurse
-        UpdateJsonValueSource(model, &child, j[i++], child.path, time);
+        UpdateJsonValueSource(model, &child, arr[i++], child.path, time);
       }
       break;
     }
-    case wpi::util::json::value_t::string:
-      out->value =
-          wpi::nt::Value::MakeString(j.get_ref<const std::string&>(), time);
+    case wpi::util::json::Type::String:
+      out->value = wpi::nt::Value::MakeString(j.get_string(), time);
       out->UpdateFromValue(model, name, "");
       break;
-    case wpi::util::json::value_t::boolean:
-      out->value = wpi::nt::Value::MakeBoolean(j.get<bool>(), time);
+    case wpi::util::json::Type::Bool:
+      out->value = wpi::nt::Value::MakeBoolean(j.get_bool(), time);
       out->UpdateFromValue(model, name, "");
       break;
-    case wpi::util::json::value_t::number_integer:
-      out->value = wpi::nt::Value::MakeInteger(j.get<int64_t>(), time);
+    case wpi::util::json::Type::Int:
+      out->value = wpi::nt::Value::MakeInteger(j.get_int(), time);
       out->UpdateFromValue(model, name, "");
       break;
-    case wpi::util::json::value_t::number_unsigned:
-      out->value = wpi::nt::Value::MakeInteger(j.get<uint64_t>(), time);
-      out->UpdateFromValue(model, name, "");
-      break;
-    case wpi::util::json::value_t::number_float:
-      out->value = wpi::nt::Value::MakeDouble(j.get<double>(), time);
+    case wpi::util::json::Type::Float:
+      out->value = wpi::nt::Value::MakeDouble(j.get_double(), time);
       out->UpdateFromValue(model, name, "");
       break;
     default:
@@ -877,12 +870,8 @@ void NetworkTablesModel::ValueSource::UpdateFromValue(
     }
     case NT_STRING:
       if (typeStr == "json") {
-        try {
-          UpdateJsonValueSource(model, this,
-                                wpi::util::json::parse(value.GetString()), name,
-                                value.last_change());
-        } catch (wpi::util::json::exception&) {
-          // ignore
+        if (auto j = wpi::util::json::parse(value.GetString())) {
+          UpdateJsonValueSource(model, this, *j, name, value.last_change());
         }
       } else {
         valueChildren.clear();
diff --git a/ntcore/src/generate/main/native/include/wpi/nt/Topic.hpp.jinja b/ntcore/src/generate/main/native/include/wpi/nt/Topic.hpp.jinja
index 71133ef0bd..6f97e1b1ad 100644
--- a/ntcore/src/generate/main/native/include/wpi/nt/Topic.hpp.jinja
+++ b/ntcore/src/generate/main/native/include/wpi/nt/Topic.hpp.jinja
@@ -13,8 +13,6 @@
 #include <string_view>
 #include <vector>
 
-#include "wpi/util/json_fwd.hpp"
-
 #include "wpi/nt/NetworkTableType.hpp"
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
@@ -22,6 +20,7 @@
 namespace wpi::util {
 template <typename T>
 class SmallVectorImpl;
+class json;
 }  // namespace wpi
 
 namespace wpi::nt {
diff --git a/ntcore/src/generated/main/native/include/wpi/nt/BooleanArrayTopic.hpp b/ntcore/src/generated/main/native/include/wpi/nt/BooleanArrayTopic.hpp
index b9cc5bfe01..3bd6321de6 100644
--- a/ntcore/src/generated/main/native/include/wpi/nt/BooleanArrayTopic.hpp
+++ b/ntcore/src/generated/main/native/include/wpi/nt/BooleanArrayTopic.hpp
@@ -13,8 +13,6 @@
 #include <string_view>
 #include <vector>
 
-#include "wpi/util/json_fwd.hpp"
-
 #include "wpi/nt/NetworkTableType.hpp"
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
@@ -22,6 +20,7 @@
 namespace wpi::util {
 template <typename T>
 class SmallVectorImpl;
+class json;
 }  // namespace wpi
 
 namespace wpi::nt {
diff --git a/ntcore/src/generated/main/native/include/wpi/nt/BooleanTopic.hpp b/ntcore/src/generated/main/native/include/wpi/nt/BooleanTopic.hpp
index 5dff0f5d42..bf52684f12 100644
--- a/ntcore/src/generated/main/native/include/wpi/nt/BooleanTopic.hpp
+++ b/ntcore/src/generated/main/native/include/wpi/nt/BooleanTopic.hpp
@@ -13,8 +13,6 @@
 #include <string_view>
 #include <vector>
 
-#include "wpi/util/json_fwd.hpp"
-
 #include "wpi/nt/NetworkTableType.hpp"
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
@@ -22,6 +20,7 @@
 namespace wpi::util {
 template <typename T>
 class SmallVectorImpl;
+class json;
 }  // namespace wpi
 
 namespace wpi::nt {
diff --git a/ntcore/src/generated/main/native/include/wpi/nt/DoubleArrayTopic.hpp b/ntcore/src/generated/main/native/include/wpi/nt/DoubleArrayTopic.hpp
index 56b4ef356d..22bd4e8b56 100644
--- a/ntcore/src/generated/main/native/include/wpi/nt/DoubleArrayTopic.hpp
+++ b/ntcore/src/generated/main/native/include/wpi/nt/DoubleArrayTopic.hpp
@@ -13,8 +13,6 @@
 #include <string_view>
 #include <vector>
 
-#include "wpi/util/json_fwd.hpp"
-
 #include "wpi/nt/NetworkTableType.hpp"
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
@@ -22,6 +20,7 @@
 namespace wpi::util {
 template <typename T>
 class SmallVectorImpl;
+class json;
 }  // namespace wpi
 
 namespace wpi::nt {
diff --git a/ntcore/src/generated/main/native/include/wpi/nt/DoubleTopic.hpp b/ntcore/src/generated/main/native/include/wpi/nt/DoubleTopic.hpp
index 0339208128..c03f7594e9 100644
--- a/ntcore/src/generated/main/native/include/wpi/nt/DoubleTopic.hpp
+++ b/ntcore/src/generated/main/native/include/wpi/nt/DoubleTopic.hpp
@@ -13,8 +13,6 @@
 #include <string_view>
 #include <vector>
 
-#include "wpi/util/json_fwd.hpp"
-
 #include "wpi/nt/NetworkTableType.hpp"
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
@@ -22,6 +20,7 @@
 namespace wpi::util {
 template <typename T>
 class SmallVectorImpl;
+class json;
 }  // namespace wpi
 
 namespace wpi::nt {
diff --git a/ntcore/src/generated/main/native/include/wpi/nt/FloatArrayTopic.hpp b/ntcore/src/generated/main/native/include/wpi/nt/FloatArrayTopic.hpp
index 55ff731b9e..ebc8dc2dc4 100644
--- a/ntcore/src/generated/main/native/include/wpi/nt/FloatArrayTopic.hpp
+++ b/ntcore/src/generated/main/native/include/wpi/nt/FloatArrayTopic.hpp
@@ -13,8 +13,6 @@
 #include <string_view>
 #include <vector>
 
-#include "wpi/util/json_fwd.hpp"
-
 #include "wpi/nt/NetworkTableType.hpp"
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
@@ -22,6 +20,7 @@
 namespace wpi::util {
 template <typename T>
 class SmallVectorImpl;
+class json;
 }  // namespace wpi
 
 namespace wpi::nt {
diff --git a/ntcore/src/generated/main/native/include/wpi/nt/FloatTopic.hpp b/ntcore/src/generated/main/native/include/wpi/nt/FloatTopic.hpp
index 0adb178b1a..d8517b4114 100644
--- a/ntcore/src/generated/main/native/include/wpi/nt/FloatTopic.hpp
+++ b/ntcore/src/generated/main/native/include/wpi/nt/FloatTopic.hpp
@@ -13,8 +13,6 @@
 #include <string_view>
 #include <vector>
 
-#include "wpi/util/json_fwd.hpp"
-
 #include "wpi/nt/NetworkTableType.hpp"
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
@@ -22,6 +20,7 @@
 namespace wpi::util {
 template <typename T>
 class SmallVectorImpl;
+class json;
 }  // namespace wpi
 
 namespace wpi::nt {
diff --git a/ntcore/src/generated/main/native/include/wpi/nt/IntegerArrayTopic.hpp b/ntcore/src/generated/main/native/include/wpi/nt/IntegerArrayTopic.hpp
index 699a1a495d..4c06c65d6e 100644
--- a/ntcore/src/generated/main/native/include/wpi/nt/IntegerArrayTopic.hpp
+++ b/ntcore/src/generated/main/native/include/wpi/nt/IntegerArrayTopic.hpp
@@ -13,8 +13,6 @@
 #include <string_view>
 #include <vector>
 
-#include "wpi/util/json_fwd.hpp"
-
 #include "wpi/nt/NetworkTableType.hpp"
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
@@ -22,6 +20,7 @@
 namespace wpi::util {
 template <typename T>
 class SmallVectorImpl;
+class json;
 }  // namespace wpi
 
 namespace wpi::nt {
diff --git a/ntcore/src/generated/main/native/include/wpi/nt/IntegerTopic.hpp b/ntcore/src/generated/main/native/include/wpi/nt/IntegerTopic.hpp
index c9f3db5fe1..4b6058fc44 100644
--- a/ntcore/src/generated/main/native/include/wpi/nt/IntegerTopic.hpp
+++ b/ntcore/src/generated/main/native/include/wpi/nt/IntegerTopic.hpp
@@ -13,8 +13,6 @@
 #include <string_view>
 #include <vector>
 
-#include "wpi/util/json_fwd.hpp"
-
 #include "wpi/nt/NetworkTableType.hpp"
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
@@ -22,6 +20,7 @@
 namespace wpi::util {
 template <typename T>
 class SmallVectorImpl;
+class json;
 }  // namespace wpi
 
 namespace wpi::nt {
diff --git a/ntcore/src/generated/main/native/include/wpi/nt/RawTopic.hpp b/ntcore/src/generated/main/native/include/wpi/nt/RawTopic.hpp
index 9df0ef01e2..171a6e8369 100644
--- a/ntcore/src/generated/main/native/include/wpi/nt/RawTopic.hpp
+++ b/ntcore/src/generated/main/native/include/wpi/nt/RawTopic.hpp
@@ -13,8 +13,6 @@
 #include <string_view>
 #include <vector>
 
-#include "wpi/util/json_fwd.hpp"
-
 #include "wpi/nt/NetworkTableType.hpp"
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
@@ -22,6 +20,7 @@
 namespace wpi::util {
 template <typename T>
 class SmallVectorImpl;
+class json;
 }  // namespace wpi
 
 namespace wpi::nt {
diff --git a/ntcore/src/generated/main/native/include/wpi/nt/StringArrayTopic.hpp b/ntcore/src/generated/main/native/include/wpi/nt/StringArrayTopic.hpp
index 4505df388e..2055a96145 100644
--- a/ntcore/src/generated/main/native/include/wpi/nt/StringArrayTopic.hpp
+++ b/ntcore/src/generated/main/native/include/wpi/nt/StringArrayTopic.hpp
@@ -13,8 +13,6 @@
 #include <string_view>
 #include <vector>
 
-#include "wpi/util/json_fwd.hpp"
-
 #include "wpi/nt/NetworkTableType.hpp"
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
@@ -22,6 +20,7 @@
 namespace wpi::util {
 template <typename T>
 class SmallVectorImpl;
+class json;
 }  // namespace wpi
 
 namespace wpi::nt {
diff --git a/ntcore/src/generated/main/native/include/wpi/nt/StringTopic.hpp b/ntcore/src/generated/main/native/include/wpi/nt/StringTopic.hpp
index 7162c85bfc..e8415154ac 100644
--- a/ntcore/src/generated/main/native/include/wpi/nt/StringTopic.hpp
+++ b/ntcore/src/generated/main/native/include/wpi/nt/StringTopic.hpp
@@ -15,8 +15,6 @@
 #include <string_view>
 #include <vector>
 
-#include "wpi/util/json_fwd.hpp"
-
 #include "wpi/nt/NetworkTableType.hpp"
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
@@ -24,6 +22,7 @@
 namespace wpi::util {
 template <typename T>
 class SmallVectorImpl;
+class json;
 }  // namespace wpi
 
 namespace wpi::nt {
diff --git a/ntcore/src/main/native/cpp/ConnectionList.cpp b/ntcore/src/main/native/cpp/ConnectionList.cpp
index 20ed596b63..f4c81af1f9 100644
--- a/ntcore/src/main/native/cpp/ConnectionList.cpp
+++ b/ntcore/src/main/native/cpp/ConnectionList.cpp
@@ -19,18 +19,17 @@ using namespace wpi::nt;
 static std::string ConnInfoToJson(bool connected, const ConnectionInfo& info) {
   std::string str;
   wpi::util::raw_string_ostream os{str};
-  wpi::util::json::serializer s{os, ' ', 0};
-  os << "{\"connected\":" << (connected ? "true" : "false");
-  os << ",\"remote_id\":\"";
-  s.dump_escaped(info.remote_id, false);
-  os << "\",\"remote_ip\":\"";
-  s.dump_escaped(info.remote_ip, false);
-  os << "\",\"remote_port\":";
-  s.dump_integer(static_cast<uint64_t>(info.remote_port));
+  os << "{\"connected\":";
+  wpi::util::json::stringify_bool(os, connected);
+  os << ",\"remote_id\":";
+  wpi::util::json::stringify_string(os, info.remote_id);
+  os << ",\"remote_ip\":";
+  wpi::util::json::stringify_string(os, info.remote_ip);
+  os << ",\"remote_port\":";
+  wpi::util::json::stringify_int(os, info.remote_port);
   os << ",\"protocol_version\":";
-  s.dump_integer(static_cast<uint64_t>(info.protocol_version));
+  wpi::util::json::stringify_int(os, info.protocol_version);
   os << "}";
-  os.flush();
   return str;
 }
 
diff --git a/ntcore/src/main/native/cpp/jni/NetworkTablesJNI.cpp b/ntcore/src/main/native/cpp/jni/NetworkTablesJNI.cpp
index 4819adcb8a..979e1b5227 100644
--- a/ntcore/src/main/native/cpp/jni/NetworkTablesJNI.cpp
+++ b/ntcore/src/main/native/cpp/jni/NetworkTablesJNI.cpp
@@ -735,7 +735,7 @@ Java_org_wpilib_networktables_NetworkTablesJNI_getTopicProperty
   (JNIEnv* env, jclass, jint topic, jstring name)
 {
   return MakeJString(
-      env, wpi::nt::GetTopicProperty(topic, JStringRef{env, name}).dump());
+      env, wpi::nt::GetTopicProperty(topic, JStringRef{env, name}).to_string());
 }
 
 /*
@@ -747,15 +747,13 @@ JNIEXPORT void JNICALL
 Java_org_wpilib_networktables_NetworkTablesJNI_setTopicProperty
   (JNIEnv* env, jclass, jint topic, jstring name, jstring value)
 {
-  wpi::util::json j;
-  try {
-    j = wpi::util::json::parse(std::string_view{JStringRef{env, value}});
-  } catch (wpi::util::json::parse_error& err) {
+  auto j = wpi::util::json::parse(std::string_view{JStringRef{env, value}});
+  if (!j) {
     illegalArgEx.Throw(
-        env, fmt::format("could not parse value JSON: {}", err.what()));
+        env, fmt::format("could not parse value JSON: {}", j.error()));
     return;
   }
-  wpi::nt::SetTopicProperty(topic, JStringRef{env, name}, j);
+  wpi::nt::SetTopicProperty(topic, JStringRef{env, name}, *j);
 }
 
 /*
@@ -779,7 +777,7 @@ JNIEXPORT jstring JNICALL
 Java_org_wpilib_networktables_NetworkTablesJNI_getTopicProperties
   (JNIEnv* env, jclass, jint topic)
 {
-  return MakeJString(env, wpi::nt::GetTopicProperties(topic).dump());
+  return MakeJString(env, wpi::nt::GetTopicProperties(topic).to_string());
 }
 
 /*
@@ -791,19 +789,18 @@ JNIEXPORT void JNICALL
 Java_org_wpilib_networktables_NetworkTablesJNI_setTopicProperties
   (JNIEnv* env, jclass, jint topic, jstring properties)
 {
-  wpi::util::json j;
-  try {
-    j = wpi::util::json::parse(std::string_view{JStringRef{env, properties}});
-  } catch (wpi::util::json::parse_error& err) {
+  auto j =
+      wpi::util::json::parse(std::string_view{JStringRef{env, properties}});
+  if (!j) {
     illegalArgEx.Throw(
-        env, fmt::format("could not parse properties JSON: {}", err.what()));
+        env, fmt::format("could not parse properties JSON: {}", j.error()));
     return;
   }
-  if (!j.is_object()) {
+  if (!j->is_object()) {
     illegalArgEx.Throw(env, "properties is not a JSON object");
     return;
   }
-  wpi::nt::SetTopicProperties(topic, j);
+  wpi::nt::SetTopicProperties(topic, *j);
 }
 
 /*
@@ -856,20 +853,19 @@ Java_org_wpilib_networktables_NetworkTablesJNI_publishEx
   (JNIEnv* env, jclass, jint topic, jint type, jstring typeStr,
    jstring properties, jobject options)
 {
-  wpi::util::json j;
-  try {
-    j = wpi::util::json::parse(std::string_view{JStringRef{env, properties}});
-  } catch (wpi::util::json::parse_error& err) {
+  auto j =
+      wpi::util::json::parse(std::string_view{JStringRef{env, properties}});
+  if (!j) {
     illegalArgEx.Throw(
-        env, fmt::format("could not parse properties JSON: {}", err.what()));
+        env, fmt::format("could not parse properties JSON: {}", j.error()));
     return 0;
   }
-  if (!j.is_object()) {
+  if (!j->is_object()) {
     illegalArgEx.Throw(env, "properties is not a JSON object");
     return 0;
   }
   return wpi::nt::PublishEx(topic, static_cast<NT_Type>(type),
-                            JStringRef{env, typeStr}, j,
+                            JStringRef{env, typeStr}, *j,
                             FromJavaPubSubOptions(env, options));
 }
 
diff --git a/ntcore/src/main/native/cpp/local/LocalStorageImpl.cpp b/ntcore/src/main/native/cpp/local/LocalStorageImpl.cpp
index 5296710f3c..34426efe13 100644
--- a/ntcore/src/main/native/cpp/local/LocalStorageImpl.cpp
+++ b/ntcore/src/main/native/cpp/local/LocalStorageImpl.cpp
@@ -40,7 +40,7 @@ void StorageImpl::NetworkAnnounce(LocalTopic* topic, std::string_view typeStr,
                                   const wpi::util::json& properties,
                                   std::optional<int> pubuid) {
   DEBUG4("LS NetworkAnnounce({}, {}, {}, {})", topic->name, typeStr,
-         properties.dump(), pubuid.value_or(-1));
+         properties.to_string(), pubuid.value_or(-1));
   if (pubuid.has_value()) {
     return;  // ack of our publish; ignore
   }
@@ -751,9 +751,10 @@ void StorageImpl::AddSchema(std::string_view name, std::string_view type,
     return;
   }
 
-  pubHandle = AddLocalPublisher(topic, {{"retained", true}},
-                                PubSubConfig{NT_RAW, type, {}})
-                  ->handle;
+  pubHandle =
+      AddLocalPublisher(topic, wpi::util::json::object("retained", true),
+                        PubSubConfig{NT_RAW, type, {}})
+          ->handle;
 
   SetDefaultEntryValue(pubHandle, Value::MakeRaw(schema));
 }
@@ -870,8 +871,8 @@ void StorageImpl::PropertiesUpdated(LocalTopic* topic,
                                     const wpi::util::json& update,
                                     unsigned int eventFlags, bool sendNetwork,
                                     bool updateFlags) {
-  DEBUG4("PropertiesUpdated({}, {}, {}, {}, {})", topic->name, update.dump(),
-         eventFlags, sendNetwork, updateFlags);
+  DEBUG4("PropertiesUpdated({}, {}, {}, {}, {})", topic->name,
+         update.to_string(), eventFlags, sendNetwork, updateFlags);
   topic->RefreshProperties(updateFlags);
   unsigned int flags = topic->GetFlags();
   if (updateFlags && (flags & NT_UNCACHED) != 0 &&
diff --git a/ntcore/src/main/native/cpp/local/LocalTopic.cpp b/ntcore/src/main/native/cpp/local/LocalTopic.cpp
index b201a4b90c..56b8ba8c27 100644
--- a/ntcore/src/main/native/cpp/local/LocalTopic.cpp
+++ b/ntcore/src/main/native/cpp/local/LocalTopic.cpp
@@ -137,11 +137,11 @@ bool LocalTopic::SetProperties(const wpi::util::json& update) {
   if (!update.is_object()) {
     return false;
   }
-  for (auto&& change : update.items()) {
-    if (change.value().is_null()) {
-      properties.erase(change.key());
+  for (auto&& [key, value] : update.get_object()) {
+    if (value.is_null()) {
+      properties.erase(key);
     } else {
-      properties[change.key()] = change.value();
+      properties[key] = value;
     }
   }
   return true;
@@ -151,22 +151,25 @@ void LocalTopic::RefreshProperties(bool updateFlags) {
   if (updateFlags) {
     RefreshFlags();
   }
-  m_propertiesStr = properties.dump();
+  m_propertiesStr = properties.to_string();
 }
 
-wpi::util::json LocalTopic::CompareProperties(const wpi::util::json props) {
+wpi::util::json LocalTopic::CompareProperties(const wpi::util::json& props) {
   wpi::util::json update = wpi::util::json::object();
   // added/changed
-  for (auto&& prop : props.items()) {
-    auto it = properties.find(prop.key());
-    if (it == properties.end() || *it != prop.value()) {
-      update[prop.key()] = prop.value();
+  if (!props.is_object()) {
+    return update;
+  }
+  for (auto&& [key, value] : props.get_object()) {
+    auto it = properties.lookup(key);
+    if (!it || *it != value) {
+      update[key] = value;
     }
   }
   // removed
-  for (auto&& prop : properties.items()) {
-    if (props.find(prop.key()) == props.end()) {
-      update[prop.key()] = wpi::util::json();
+  for (auto&& [key, value] : properties.get_object()) {
+    if (!props.contains(key)) {
+      update[key] = wpi::util::json();
     }
   }
   return update;
@@ -187,30 +190,27 @@ void LocalTopic::ResetIfDoesNotExist() {
 }
 
 void LocalTopic::RefreshFlags() {
-  auto it = properties.find("persistent");
-  if (it != properties.end()) {
-    if (auto val = it->get_ptr<bool*>()) {
-      if (*val) {
+  if (auto persistent = properties.lookup("persistent")) {
+    if (persistent->is_bool()) {
+      if (persistent->get_bool()) {
         m_flags |= NT_PERSISTENT;
       } else {
         m_flags &= ~NT_PERSISTENT;
       }
     }
   }
-  it = properties.find("retained");
-  if (it != properties.end()) {
-    if (auto val = it->get_ptr<bool*>()) {
-      if (*val) {
+  if (auto retained = properties.lookup("retained")) {
+    if (retained->is_bool()) {
+      if (retained->get_bool()) {
         m_flags |= NT_RETAINED;
       } else {
         m_flags &= ~NT_RETAINED;
       }
     }
   }
-  it = properties.find("cached");
-  if (it != properties.end()) {
-    if (auto val = it->get_ptr<bool*>()) {
-      if (*val) {
+  if (auto cached = properties.lookup("cached")) {
+    if (cached->is_bool()) {
+      if (cached->get_bool()) {
         m_flags &= ~NT_UNCACHED;
       } else {
         m_flags |= NT_UNCACHED;
diff --git a/ntcore/src/main/native/cpp/local/LocalTopic.hpp b/ntcore/src/main/native/cpp/local/LocalTopic.hpp
index 2bb67e6a5a..913218b1fd 100644
--- a/ntcore/src/main/native/cpp/local/LocalTopic.hpp
+++ b/ntcore/src/main/native/cpp/local/LocalTopic.hpp
@@ -62,7 +62,7 @@ struct LocalTopic {
   void RefreshProperties(bool updateFlags);
 
   // returns update json
-  wpi::util::json CompareProperties(const wpi::util::json props);
+  wpi::util::json CompareProperties(const wpi::util::json& props);
 
   TopicInfo GetTopicInfo() const {
     TopicInfo info;
diff --git a/ntcore/src/main/native/cpp/net/ClientImpl.cpp b/ntcore/src/main/native/cpp/net/ClientImpl.cpp
index 3f2aae1291..724c0672b6 100644
--- a/ntcore/src/main/native/cpp/net/ClientImpl.cpp
+++ b/ntcore/src/main/native/cpp/net/ClientImpl.cpp
@@ -240,7 +240,7 @@ void ClientImpl::ServerUnannounce(std::string_view name, int id) {
 void ClientImpl::ServerPropertiesUpdate(std::string_view name,
                                         const wpi::util::json& update,
                                         bool ack) {
-  DEBUG4("ServerProperties({}, {}, {})", name, update.dump(), ack);
+  DEBUG4("ServerProperties({}, {}, {})", name, update.to_string(), ack);
   assert(m_local);
   m_local->ServerPropertiesUpdate(name, update, ack);
 }
diff --git a/ntcore/src/main/native/cpp/net/MessageHandler.hpp b/ntcore/src/main/native/cpp/net/MessageHandler.hpp
index daba1060d5..7381d24da3 100644
--- a/ntcore/src/main/native/cpp/net/MessageHandler.hpp
+++ b/ntcore/src/main/native/cpp/net/MessageHandler.hpp
@@ -9,7 +9,9 @@
 #include <string>
 #include <string_view>
 
-#include "wpi/util/json_fwd.hpp"
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::nt {
 class PubSubOptionsImpl;
diff --git a/ntcore/src/main/native/cpp/net/NetworkOutgoingQueue.hpp b/ntcore/src/main/native/cpp/net/NetworkOutgoingQueue.hpp
index e9250369ab..75d5390618 100644
--- a/ntcore/src/main/native/cpp/net/NetworkOutgoingQueue.hpp
+++ b/ntcore/src/main/native/cpp/net/NetworkOutgoingQueue.hpp
@@ -20,6 +20,8 @@
 #include "wpi/nt/NetworkTableValue.hpp"
 #include "wpi/nt/ntcore_c.h"
 #include "wpi/util/DenseMap.hpp"
+#include "wpi/util/SmallVector.hpp"
+#include "wpi/util/raw_ostream.hpp"
 
 namespace wpi::nt::net {
 
diff --git a/ntcore/src/main/native/cpp/net/WireDecoder.cpp b/ntcore/src/main/native/cpp/net/WireDecoder.cpp
index c588752213..861ac91872 100644
--- a/ntcore/src/main/native/cpp/net/WireDecoder.cpp
+++ b/ntcore/src/main/native/cpp/net/WireDecoder.cpp
@@ -24,12 +24,8 @@ using namespace wpi::nt::net;
 using namespace mpack;
 
 static bool GetNumber(wpi::util::json& val, double* num) {
-  if (auto v = val.get_ptr<const int64_t*>()) {
-    *num = *v;
-  } else if (auto v = val.get_ptr<const uint64_t*>()) {
-    *num = *v;
-  } else if (auto v = val.get_ptr<const double*>()) {
-    *num = *v;
+  if (val.is_number()) {
+    *num = val.get_number();
   } else {
     return false;
   }
@@ -37,67 +33,64 @@ static bool GetNumber(wpi::util::json& val, double* num) {
 }
 
 static bool GetNumber(wpi::util::json& val, int64_t* num) {
-  if (auto v = val.get_ptr<const int64_t*>()) {
-    *num = *v;
-  } else if (auto v = val.get_ptr<const uint64_t*>()) {
-    *num = *v;
+  if (val.is_int()) {
+    *num = val.get_int();
   } else {
     return false;
   }
   return true;
 }
 
-static std::string* ObjGetString(wpi::util::json::object_t& obj,
-                                 std::string_view key, std::string* error) {
-  auto it = obj.find(key);
-  if (it == obj.end()) {
+static std::string* ObjGetString(wpi::util::json& obj, std::string_view key,
+                                 std::string* error) {
+  auto val = obj.lookup(key);
+  if (!val) {
     *error = fmt::format("no {} key", key);
     return nullptr;
   }
-  auto val = it->second.get_ptr<std::string*>();
-  if (!val) {
+  if (!val->is_string()) {
     *error = fmt::format("{} must be a string", key);
+    return nullptr;
   }
-  return val;
+  return &val->get_string();
 }
 
-static bool ObjGetNumber(wpi::util::json::object_t& obj, std::string_view key,
+static bool ObjGetNumber(wpi::util::json& obj, std::string_view key,
                          std::string* error, int64_t* num) {
-  auto it = obj.find(key);
-  if (it == obj.end()) {
+  auto val = obj.lookup(key);
+  if (!val) {
     *error = fmt::format("no {} key", key);
     return false;
   }
-  if (!GetNumber(it->second, num)) {
+  if (!GetNumber(*val, num)) {
     *error = fmt::format("{} must be a number", key);
     return false;
   }
   return true;
 }
 
-static bool ObjGetStringArray(wpi::util::json::object_t& obj,
-                              std::string_view key, std::string* error,
+static bool ObjGetStringArray(wpi::util::json& obj, std::string_view key,
+                              std::string* error,
                               std::vector<std::string>* out) {
   // prefixes
-  auto it = obj.find(key);
-  if (it == obj.end()) {
+  auto val = obj.lookup(key);
+  if (!val) {
     *error = fmt::format("no {} key", key);
     return false;
   }
-  auto jarr = it->second.get_ptr<wpi::util::json::array_t*>();
-  if (!jarr) {
+  if (!val->is_array()) {
     *error = fmt::format("{} must be an array", key);
     return false;
   }
+  auto& arr = val->get_array();
   out->resize(0);
-  out->reserve(jarr->size());
-  for (auto&& jval : *jarr) {
-    auto str = jval.get_ptr<std::string*>();
-    if (!str) {
+  out->reserve(arr.size());
+  for (auto&& jval : arr) {
+    if (!jval.is_string()) {
       *error = fmt::format("{}/{} must be a string", key, out->size());
       return false;
     }
-    out->emplace_back(std::move(*str));
+    out->emplace_back(jval.get_string());
   }
   return true;
 }
@@ -113,43 +106,39 @@ template <typename T>
            std::same_as<T, ServerMessageHandler>)
 static bool WireDecodeTextImpl(std::string_view in, T& out,
                                wpi::util::Logger& logger) {
-  wpi::util::json j;
-  try {
-    j = wpi::util::json::parse(in);
-  } catch (wpi::util::json::parse_error& err) {
-    WPI_WARNING(logger, "could not decode JSON message: {}", err.what());
+  auto j = wpi::util::json::parse(in);
+  if (!j) {
+    WPI_WARNING(logger, "could not decode JSON message: {}", j.error());
     return false;
   }
 
-  if (!j.is_array()) {
+  if (!j->is_array()) {
     WPI_WARNING(logger, "expected JSON array at top level");
     return false;
   }
 
   bool rv = false;
   int i = -1;
-  for (auto&& jmsg : j) {
+  for (auto&& jmsg : j->get_array()) {
     ++i;
     std::string error;
     {
-      auto obj = jmsg.get_ptr<wpi::util::json::object_t*>();
-      if (!obj) {
+      if (!jmsg.is_object()) {
         error = "expected message to be an object";
         goto err;
       }
 
-      auto method = ObjGetString(*obj, "method", &error);
+      auto method = ObjGetString(jmsg, "method", &error);
       if (!method) {
         goto err;
       }
 
-      auto paramsIt = obj->find("params");
-      if (paramsIt == obj->end()) {
+      auto params = jmsg.lookup("params");
+      if (!params) {
         error = "no params key";
         goto err;
       }
-      auto params = paramsIt->second.get_ptr<wpi::util::json::object_t*>();
-      if (!params) {
+      if (!params->is_object()) {
         error = "params must be an object";
         goto err;
       }
@@ -182,14 +171,10 @@ static bool WireDecodeTextImpl(std::string_view in, T& out,
           }
 
           // properties; allow missing (treated as empty)
-          wpi::util::json* properties = nullptr;
-          auto propertiesIt = params->find("properties");
-          if (propertiesIt != params->end()) {
-            properties = &propertiesIt->second;
-            if (!properties->is_object()) {
-              error = "properties must be an object";
-              goto err;
-            }
+          auto properties = params->lookup("properties");
+          if (properties && !properties->is_object()) {
+            error = "properties must be an object";
+            goto err;
           }
           wpi::util::json propertiesEmpty;
           if (!properties) {
@@ -225,12 +210,11 @@ static bool WireDecodeTextImpl(std::string_view in, T& out,
           }
 
           // update
-          auto updateIt = params->find("update");
-          if (updateIt == params->end()) {
+          auto update = params->lookup("update");
+          if (!update) {
             error = "no update key";
             goto err;
           }
-          auto update = &updateIt->second;
           if (!update->is_object()) {
             error = "update must be an object";
             goto err;
@@ -254,20 +238,16 @@ static bool WireDecodeTextImpl(std::string_view in, T& out,
 
           // options
           PubSubOptionsImpl options;
-          auto optionsIt = params->find("options");
-          if (optionsIt != params->end()) {
-            auto joptions =
-                optionsIt->second.get_ptr<wpi::util::json::object_t*>();
-            if (!joptions) {
+          if (auto joptions = params->lookup("options")) {
+            if (!joptions->is_object()) {
               error = "options must be an object";
               goto err;
             }
 
             // periodic
-            auto periodicIt = joptions->find("periodic");
-            if (periodicIt != joptions->end()) {
+            if (auto periodic = joptions->lookup("periodic")) {
               double val;
-              if (!GetNumber(periodicIt->second, &val)) {
+              if (!GetNumber(*periodic, &val)) {
                 error = "periodic value must be a number";
                 goto err;
               }
@@ -276,36 +256,30 @@ static bool WireDecodeTextImpl(std::string_view in, T& out,
             }
 
             // send all changes
-            auto sendAllIt = joptions->find("all");
-            if (sendAllIt != joptions->end()) {
-              auto sendAll = sendAllIt->second.get_ptr<bool*>();
-              if (!sendAll) {
+            if (auto sendAll = joptions->lookup("all")) {
+              if (!sendAll->is_bool()) {
                 error = "all value must be a boolean";
                 goto err;
               }
-              options.sendAll = *sendAll;
+              options.sendAll = sendAll->get_bool();
             }
 
             // topics only
-            auto topicsOnlyIt = joptions->find("topicsonly");
-            if (topicsOnlyIt != joptions->end()) {
-              auto topicsOnly = topicsOnlyIt->second.get_ptr<bool*>();
-              if (!topicsOnly) {
+            if (auto topicsOnly = joptions->lookup("topicsonly")) {
+              if (!topicsOnly->is_bool()) {
                 error = "topicsonly value must be a boolean";
                 goto err;
               }
-              options.topicsOnly = *topicsOnly;
+              options.topicsOnly = topicsOnly->get_bool();
             }
 
             // prefix match
-            auto prefixMatchIt = joptions->find("prefix");
-            if (prefixMatchIt != joptions->end()) {
-              auto prefixMatch = prefixMatchIt->second.get_ptr<bool*>();
-              if (!prefixMatch) {
+            if (auto prefixMatch = joptions->lookup("prefix")) {
+              if (!prefixMatch->is_bool()) {
                 error = "prefix value must be a boolean";
                 goto err;
               }
-              options.prefixMatch = *prefixMatch;
+              options.prefixMatch = prefixMatch->get_bool();
             }
           }
 
@@ -368,10 +342,9 @@ static bool WireDecodeTextImpl(std::string_view in, T& out,
 
           // pubuid
           std::optional<int64_t> pubuid;
-          auto pubuidIt = params->find("pubuid");
-          if (pubuidIt != params->end()) {
+          if (auto jpubuid = params->lookup("pubuid")) {
             int64_t val;
-            if (!GetNumber(pubuidIt->second, &val)) {
+            if (!GetNumber(*jpubuid, &val)) {
               error = "pubuid value must be a number";
               goto err;
             }
@@ -387,12 +360,11 @@ static bool WireDecodeTextImpl(std::string_view in, T& out,
           }
 
           // properties
-          auto propertiesIt = params->find("properties");
-          if (propertiesIt == params->end()) {
+          auto properties = params->lookup("properties");
+          if (!properties) {
             error = "no properties key";
             goto err;
           }
-          auto properties = &propertiesIt->second;
           if (!properties->is_object()) {
             WPI_WARNING(logger, "{}: properties is not an object", *name);
             *properties = wpi::util::json::object();
@@ -430,26 +402,23 @@ static bool WireDecodeTextImpl(std::string_view in, T& out,
           }
 
           // update
-          auto updateIt = params->find("update");
-          if (updateIt == params->end()) {
+          auto update = params->lookup("update");
+          if (!update) {
             error = "no update key";
             goto err;
           }
-          auto update = &updateIt->second;
           if (!update->is_object()) {
             error = "update must be an object";
             goto err;
           }
 
           bool ack = false;
-          auto ackIt = params->find("ack");
-          if (ackIt != params->end()) {
-            auto val = ackIt->second.get_ptr<bool*>();
-            if (!val) {
+          if (auto jack = params->lookup("ack")) {
+            if (!jack->is_bool()) {
               error = "ack must be a boolean";
               goto err;
             }
-            ack = *val;
+            ack = jack->get_bool();
           }
 
           // complete
diff --git a/ntcore/src/main/native/cpp/net/WireEncoder.cpp b/ntcore/src/main/native/cpp/net/WireEncoder.cpp
index ee0529354b..ddb4860cc3 100644
--- a/ntcore/src/main/native/cpp/net/WireEncoder.cpp
+++ b/ntcore/src/main/native/cpp/net/WireEncoder.cpp
@@ -22,43 +22,39 @@ void wpi::nt::net::WireEncodePublish(wpi::util::raw_ostream& os, int pubuid,
                                      std::string_view name,
                                      std::string_view typeStr,
                                      const wpi::util::json& properties) {
-  wpi::util::json::serializer s{os, ' ', 0};
   os << "{\"method\":\"" << PublishMsg::kMethodStr << "\",\"params\":{";
-  os << "\"name\":\"";
-  s.dump_escaped(name, false);
-  os << "\",\"properties\":";
-  s.dump(properties, false, false, 0, 0);
+  os << "\"name\":";
+  wpi::util::json::stringify_string(os, name);
+  os << ",\"properties\":";
+  properties.marshal(os);
   os << ",\"pubuid\":";
-  s.dump_integer(pubuid);
-  os << ",\"type\":\"";
-  s.dump_escaped(typeStr, false);
-  os << "\"}}";
+  wpi::util::json::stringify_int(os, pubuid);
+  os << ",\"type\":";
+  wpi::util::json::stringify_string(os, typeStr);
+  os << "}}";
 }
 
 void wpi::nt::net::WireEncodeUnpublish(wpi::util::raw_ostream& os, int pubuid) {
-  wpi::util::json::serializer s{os, ' ', 0};
   os << "{\"method\":\"" << UnpublishMsg::kMethodStr << "\",\"params\":{";
   os << "\"pubuid\":";
-  s.dump_integer(pubuid);
+  wpi::util::json::stringify_int(os, pubuid);
   os << "}}";
 }
 
 void wpi::nt::net::WireEncodeSetProperties(wpi::util::raw_ostream& os,
                                            std::string_view name,
                                            const wpi::util::json& update) {
-  wpi::util::json::serializer s{os, ' ', 0};
   os << "{\"method\":\"" << SetPropertiesMsg::kMethodStr << "\",\"params\":{";
-  os << "\"name\":\"";
-  s.dump_escaped(name, false);
-  os << "\",\"update\":";
-  s.dump(update, false, false, 0, 0);
+  os << "\"name\":";
+  wpi::util::json::stringify_string(os, name);
+  os << ",\"update\":";
+  update.marshal(os);
   os << "}}";
 }
 
 template <typename T>
 static void EncodePrefixes(wpi::util::raw_ostream& os,
-                           std::span<const T> topicNames,
-                           wpi::util::json::serializer& s) {
+                           std::span<const T> topicNames) {
   os << '[';
   bool first = true;
   for (auto&& name : topicNames) {
@@ -67,9 +63,7 @@ static void EncodePrefixes(wpi::util::raw_ostream& os,
     } else {
       os << ',';
     }
-    os << '"';
-    s.dump_escaped(name, false);
-    os << '"';
+    wpi::util::json::stringify_string(os, name);
   }
   os << ']';
 }
@@ -78,7 +72,6 @@ template <typename T>
 static void WireEncodeSubscribeImpl(wpi::util::raw_ostream& os, int subuid,
                                     std::span<const T> topicNames,
                                     const PubSubOptionsImpl& options) {
-  wpi::util::json::serializer s{os, ' ', 0};
   os << "{\"method\":\"" << SubscribeMsg::kMethodStr << "\",\"params\":{";
   os << "\"options\":{";
   bool first = true;
@@ -105,12 +98,12 @@ static void WireEncodeSubscribeImpl(wpi::util::raw_ostream& os, int subuid,
       os << ',';
     }
     os << "\"periodic\":";
-    s.dump_float(options.periodicMs / 1000.0);
+    wpi::util::json::stringify_float(os, options.periodicMs / 1000.0);
   }
   os << "},\"topics\":";
-  EncodePrefixes(os, topicNames, s);
+  EncodePrefixes(os, topicNames);
   os << ",\"subuid\":";
-  s.dump_integer(subuid);
+  wpi::util::json::stringify_int(os, subuid);
   os << "}}";
 }
 
@@ -129,10 +122,9 @@ void wpi::nt::net::WireEncodeSubscribe(wpi::util::raw_ostream& os, int subuid,
 
 void wpi::nt::net::WireEncodeUnsubscribe(wpi::util::raw_ostream& os,
                                          int subuid) {
-  wpi::util::json::serializer s{os, ' ', 0};
   os << "{\"method\":\"" << UnsubscribeMsg::kMethodStr << "\",\"params\":{";
   os << "\"subuid\":";
-  s.dump_integer(subuid);
+  wpi::util::json::stringify_int(os, subuid);
   os << "}}";
 }
 
@@ -159,45 +151,42 @@ void wpi::nt::net::WireEncodeAnnounce(wpi::util::raw_ostream& os,
                                       std::string_view typeStr,
                                       const wpi::util::json& properties,
                                       std::optional<int> pubuid) {
-  wpi::util::json::serializer s{os, ' ', 0};
   os << "{\"method\":\"" << AnnounceMsg::kMethodStr << "\",\"params\":{";
   os << "\"id\":";
-  s.dump_integer(id);
-  os << ",\"name\":\"";
-  s.dump_escaped(name, false);
-  os << "\",\"properties\":";
-  s.dump(properties, false, false, 0, 0);
+  wpi::util::json::stringify_int(os, id);
+  os << ",\"name\":";
+  wpi::util::json::stringify_string(os, name);
+  os << ",\"properties\":";
+  properties.marshal(os);
   if (pubuid) {
     os << ",\"pubuid\":";
-    s.dump_integer(*pubuid);
+    wpi::util::json::stringify_int(os, *pubuid);
   }
-  os << ",\"type\":\"";
-  s.dump_escaped(typeStr, false);
-  os << "\"}}";
+  os << ",\"type\":";
+  wpi::util::json::stringify_string(os, typeStr);
+  os << "}}";
 }
 
 void wpi::nt::net::WireEncodeUnannounce(wpi::util::raw_ostream& os,
                                         std::string_view name, int64_t id) {
-  wpi::util::json::serializer s{os, ' ', 0};
   os << "{\"method\":\"" << UnannounceMsg::kMethodStr << "\",\"params\":{";
   os << "\"id\":";
-  s.dump_integer(id);
-  os << ",\"name\":\"";
-  s.dump_escaped(name, false);
-  os << "\"}}";
+  wpi::util::json::stringify_int(os, id);
+  os << ",\"name\":";
+  wpi::util::json::stringify_string(os, name);
+  os << "}}";
 }
 
 void wpi::nt::net::WireEncodePropertiesUpdate(wpi::util::raw_ostream& os,
                                               std::string_view name,
                                               const wpi::util::json& update,
                                               bool ack) {
-  wpi::util::json::serializer s{os, ' ', 0};
   os << "{\"method\":\"" << PropertiesUpdateMsg::kMethodStr
      << "\",\"params\":{";
-  os << "\"name\":\"";
-  s.dump_escaped(name, false);
-  os << "\",\"update\":";
-  s.dump(update, false, false, 0, 0);
+  os << "\"name\":";
+  wpi::util::json::stringify_string(os, name);
+  os << ",\"update\":";
+  update.marshal(os);
   if (ack) {
     os << ",\"ack\":true";
   }
diff --git a/ntcore/src/main/native/cpp/net/WireEncoder.hpp b/ntcore/src/main/native/cpp/net/WireEncoder.hpp
index a016b876ea..ee357f9530 100644
--- a/ntcore/src/main/native/cpp/net/WireEncoder.hpp
+++ b/ntcore/src/main/native/cpp/net/WireEncoder.hpp
@@ -9,9 +9,8 @@
 #include <string>
 #include <string_view>
 
-#include "wpi/util/json_fwd.hpp"
-
 namespace wpi::util {
+class json;
 class raw_ostream;
 }  // namespace wpi::util
 
diff --git a/ntcore/src/main/native/cpp/ntcore_c.cpp b/ntcore/src/main/native/cpp/ntcore_c.cpp
index 2550708c0a..efdf555473 100644
--- a/ntcore/src/main/native/cpp/ntcore_c.cpp
+++ b/ntcore/src/main/native/cpp/ntcore_c.cpp
@@ -10,6 +10,7 @@
 #include <cstdlib>
 #include <cstring>
 #include <string_view>
+#include <utility>
 #include <vector>
 
 #include "Value_internal.hpp"
@@ -313,18 +314,16 @@ void NT_GetTopicProperty(NT_Topic topic, const struct WPI_String* name,
                          struct WPI_String* prop) {
   wpi::util::json j =
       wpi::nt::GetTopicProperty(topic, wpi::util::to_string_view(name));
-  wpi::nt::ConvertToC(j.dump(), prop);
+  wpi::nt::ConvertToC(j.to_string(), prop);
 }
 
 NT_Bool NT_SetTopicProperty(NT_Topic topic, const struct WPI_String* name,
                             const struct WPI_String* value) {
-  wpi::util::json j;
-  try {
-    j = wpi::util::json::parse(wpi::util::to_string_view(value));
-  } catch (wpi::util::json::parse_error&) {
+  auto j = wpi::util::json::parse(wpi::util::to_string_view(value));
+  if (!j) {
     return false;
   }
-  wpi::nt::SetTopicProperty(topic, wpi::util::to_string_view(name), j);
+  wpi::nt::SetTopicProperty(topic, wpi::util::to_string_view(name), *j);
   return true;
 }
 
@@ -334,18 +333,16 @@ void NT_DeleteTopicProperty(NT_Topic topic, const struct WPI_String* name) {
 
 void NT_GetTopicProperties(NT_Topic topic, struct WPI_String* property) {
   wpi::util::json j = wpi::nt::GetTopicProperties(topic);
-  wpi::nt::ConvertToC(j.dump(), property);
+  wpi::nt::ConvertToC(j.to_string(), property);
 }
 
 NT_Bool NT_SetTopicProperties(NT_Topic topic,
                               const struct WPI_String* properties) {
-  wpi::util::json j;
-  try {
-    j = wpi::util::json::parse(wpi::util::to_string_view(properties));
-  } catch (wpi::util::json::parse_error&) {
+  auto j = wpi::util::json::parse(wpi::util::to_string_view(properties));
+  if (!j) {
     return false;
   }
-  return wpi::nt::SetTopicProperties(topic, j);
+  return wpi::nt::SetTopicProperties(topic, *j);
 }
 
 NT_Subscriber NT_Subscribe(NT_Topic topic, NT_Type type,
@@ -375,11 +372,11 @@ NT_Publisher NT_PublishEx(NT_Topic topic, NT_Type type,
     // gracefully handle empty string
     j = wpi::util::json::object();
   } else {
-    try {
-      j = wpi::util::json::parse(wpi::util::to_string_view(properties));
-    } catch (wpi::util::json::parse_error&) {
+    auto ex = wpi::util::json::parse(wpi::util::to_string_view(properties));
+    if (!ex) {
       return {};
     }
+    j = std::move(*ex);
   }
 
   return wpi::nt::PublishEx(topic, type, wpi::util::to_string_view(typeStr), j,
diff --git a/ntcore/src/main/native/cpp/ntcore_cpp.cpp b/ntcore/src/main/native/cpp/ntcore_cpp.cpp
index fa5be9558a..c2467260c3 100644
--- a/ntcore/src/main/native/cpp/ntcore_cpp.cpp
+++ b/ntcore/src/main/native/cpp/ntcore_cpp.cpp
@@ -29,11 +29,7 @@ static std::atomic<int64_t> gNowTime;
 namespace wpi::nt {
 
 wpi::util::json TopicInfo::GetProperties() const {
-  try {
-    return wpi::util::json::parse(properties);
-  } catch (wpi::util::json::parse_error&) {
-    return wpi::util::json::object();
-  }
+  return wpi::util::json::parse(properties).value_or(wpi::util::json::object());
 }
 
 /*
diff --git a/ntcore/src/main/native/cpp/server/ServerClient.hpp b/ntcore/src/main/native/cpp/server/ServerClient.hpp
index 59ec3fcba8..c4c90272a7 100644
--- a/ntcore/src/main/native/cpp/server/ServerClient.hpp
+++ b/ntcore/src/main/native/cpp/server/ServerClient.hpp
@@ -17,9 +17,9 @@
 #include "server/Functions.hpp"
 #include "server/ServerPublisher.hpp"
 #include "server/ServerSubscriber.hpp"
-#include "wpi/util/json_fwd.hpp"
 
 namespace wpi::util {
+class json;
 class Logger;
 template <typename T>
 class SmallVectorImpl;
diff --git a/ntcore/src/main/native/cpp/server/ServerClient4Base.cpp b/ntcore/src/main/native/cpp/server/ServerClient4Base.cpp
index e768d068ca..e1a090a978 100644
--- a/ntcore/src/main/native/cpp/server/ServerClient4Base.cpp
+++ b/ntcore/src/main/native/cpp/server/ServerClient4Base.cpp
@@ -4,6 +4,7 @@
 
 #include "ServerClient4Base.hpp"
 
+#include <algorithm>
 #include <memory>
 #include <string>
 #include <vector>
@@ -38,7 +39,8 @@ void ServerClient4Base::ClientPublish(int pubuid, std::string_view name,
   }
 
   // respond with announce with pubuid to client
-  DEBUG4("client {}: announce {} pubuid {}", m_id, topic->name, pubuid);
+  DEBUG4("client {}: announce {} pubuid {} properties {}", m_id, topic->name,
+         pubuid, properties.to_string());
   SendAnnounce(topic, pubuid);
 }
 
@@ -68,18 +70,18 @@ void ServerClient4Base::ClientUnpublish(int pubuid) {
 
 void ServerClient4Base::ClientSetProperties(std::string_view name,
                                             const wpi::util::json& update) {
-  DEBUG4("ClientSetProperties({}, {}, {})", m_id, name, update.dump());
+  DEBUG4("ClientSetProperties({}, {}, {})", m_id, name, update.to_string());
   ServerTopic* topic = m_storage.GetTopic(name);
   if (!topic || !topic->IsPublished()) {
     WARN(
         "server ignoring SetProperties({}) from client {} on unpublished topic "
         "'{}'; publish or set a value first",
-        update.dump(), m_id, name);
+        update.to_string(), m_id, name);
     return;  // nothing to do
   }
   if (topic->special) {
     WARN("server ignoring SetProperties({}) from client {} on meta topic '{}'",
-         update.dump(), m_id, name);
+         update.to_string(), m_id, name);
     return;  // nothing to do
   }
   m_storage.SetProperties(nullptr, topic, update);
diff --git a/ntcore/src/main/native/cpp/server/ServerClient4Base.hpp b/ntcore/src/main/native/cpp/server/ServerClient4Base.hpp
index 1f035de321..872b7495d8 100644
--- a/ntcore/src/main/native/cpp/server/ServerClient4Base.hpp
+++ b/ntcore/src/main/native/cpp/server/ServerClient4Base.hpp
@@ -4,6 +4,7 @@
 
 #pragma once
 
+#include <array>
 #include <string>
 #include <string_view>
 
diff --git a/ntcore/src/main/native/cpp/server/ServerImpl.cpp b/ntcore/src/main/native/cpp/server/ServerImpl.cpp
index 4ce79752be..186bd70893 100644
--- a/ntcore/src/main/native/cpp/server/ServerImpl.cpp
+++ b/ntcore/src/main/native/cpp/server/ServerImpl.cpp
@@ -111,7 +111,8 @@ void ServerImpl::SendAnnounce(ServerTopic* topic, ServerClient* client) {
       continue;  // don't announce to requesting client again
     }
 
-    DEBUG4("client {}: announce {}", aClient->GetId(), topic->name);
+    DEBUG4("client {}: announce {} properties {}", aClient->GetId(),
+           topic->name, topic->properties.to_string());
     aClient->SendAnnounce(topic, std::nullopt);
   }
 }
diff --git a/ntcore/src/main/native/cpp/server/ServerStorage.cpp b/ntcore/src/main/native/cpp/server/ServerStorage.cpp
index c039fcdd32..03fbce5810 100644
--- a/ntcore/src/main/native/cpp/server/ServerStorage.cpp
+++ b/ntcore/src/main/native/cpp/server/ServerStorage.cpp
@@ -36,6 +36,8 @@ ServerTopic* ServerStorage::CreateTopic(ServerClient* client,
       }
     }
   } else {
+    DEBUG4("creating topic '{}' with type '{}' and properties {}", name,
+           typeStr, properties.to_string());
     // new topic
     unsigned int id = m_topics.emplace_back(
         std::make_unique<ServerTopic>(m_logger, name, typeStr, properties));
@@ -58,7 +60,8 @@ ServerTopic* ServerStorage::CreateTopic(ServerClient* client,
 }
 
 ServerTopic* ServerStorage::CreateMetaTopic(std::string_view name) {
-  return CreateTopic(nullptr, name, "msgpack", {{"retained", true}}, true);
+  return CreateTopic(nullptr, name, "msgpack",
+                     wpi::util::json::object("retained", true), true);
 }
 
 void ServerStorage::DeleteTopic(ServerTopic* topic) {
@@ -90,7 +93,7 @@ void ServerStorage::DeleteTopic(ServerTopic* topic) {
 void ServerStorage::SetProperties(ServerClient* client, ServerTopic* topic,
                                   const wpi::util::json& update) {
   DEBUG4("SetProperties({}, {}, {})", client ? client->GetId() : -1,
-         topic->name, update.dump());
+         topic->name, update.to_string());
   bool wasPersistent = topic->persistent;
   if (topic->SetProperties(update)) {
     // update persistentChanged flag
@@ -110,9 +113,10 @@ void ServerStorage::SetFlags(ServerClient* client, ServerTopic* topic,
       m_persistentChanged = true;
       wpi::util::json update;
       if (topic->persistent) {
-        update = {{"persistent", true}};
+        update = wpi::util::json::object("persistent", true);
       } else {
-        update = {{"persistent", wpi::util::json::object()}};
+        update =
+            wpi::util::json::object("persistent", wpi::util::json::object());
       }
       PropertiesChanged(client, topic, update);
     }
@@ -234,29 +238,22 @@ void ServerStorage::PropertiesChanged(ServerClient* client, ServerTopic* topic,
   }
 }
 
-static void DumpValue(wpi::util::raw_ostream& os, const Value& value,
-                      wpi::util::json::serializer& s) {
+static void DumpValue(wpi::util::raw_ostream& os, const Value& value) {
   switch (value.type()) {
     case NT_BOOLEAN:
-      if (value.GetBoolean()) {
-        os << "true";
-      } else {
-        os << "false";
-      }
+      wpi::util::json::stringify_bool(os, value.GetBoolean());
       break;
     case NT_DOUBLE:
-      s.dump_float(value.GetDouble());
+      wpi::util::json::stringify_double(os, value.GetDouble());
       break;
     case NT_FLOAT:
-      s.dump_float(value.GetFloat());
+      wpi::util::json::stringify_float(os, value.GetFloat());
       break;
     case NT_INTEGER:
-      s.dump_integer(value.GetInteger());
+      wpi::util::json::stringify_int(os, value.GetInteger());
       break;
     case NT_STRING:
-      os << '"';
-      s.dump_escaped(value.GetString(), false);
-      os << '"';
+      wpi::util::json::stringify_string(os, value.GetString());
       break;
     case NT_RAW:
     case NT_RPC:
@@ -273,11 +270,7 @@ static void DumpValue(wpi::util::raw_ostream& os, const Value& value,
         } else {
           os << ", ";
         }
-        if (v) {
-          os << "true";
-        } else {
-          os << "false";
-        }
+        wpi::util::json::stringify_bool(os, v);
       }
       os << ']';
       break;
@@ -291,7 +284,7 @@ static void DumpValue(wpi::util::raw_ostream& os, const Value& value,
         } else {
           os << ", ";
         }
-        s.dump_float(v);
+        wpi::util::json::stringify_double(os, v);
       }
       os << ']';
       break;
@@ -305,7 +298,7 @@ static void DumpValue(wpi::util::raw_ostream& os, const Value& value,
         } else {
           os << ", ";
         }
-        s.dump_float(v);
+        wpi::util::json::stringify_float(os, v);
       }
       os << ']';
       break;
@@ -319,7 +312,7 @@ static void DumpValue(wpi::util::raw_ostream& os, const Value& value,
         } else {
           os << ", ";
         }
-        s.dump_integer(v);
+        wpi::util::json::stringify_int(os, v);
       }
       os << ']';
       break;
@@ -333,9 +326,7 @@ static void DumpValue(wpi::util::raw_ostream& os, const Value& value,
         } else {
           os << ", ";
         }
-        os << '"';
-        s.dump_escaped(v, false);
-        os << '"';
+        wpi::util::json::stringify_string(os, v);
       }
       os << ']';
       break;
@@ -347,7 +338,6 @@ static void DumpValue(wpi::util::raw_ostream& os, const Value& value,
 }
 
 void ServerStorage::DumpPersistent(wpi::util::raw_ostream& os) {
-  wpi::util::json::serializer s{os, ' ', 16};
   os << "[\n";
   bool first = true;
   for (const auto& topic : m_topics) {
@@ -359,31 +349,31 @@ void ServerStorage::DumpPersistent(wpi::util::raw_ostream& os) {
     } else {
       os << ",\n";
     }
-    os << "  {\n    \"name\": \"";
-    s.dump_escaped(topic->name, false);
-    os << "\",\n    \"type\": \"";
-    s.dump_escaped(topic->typeStr, false);
-    os << "\",\n    \"value\": ";
-    DumpValue(os, topic->lastValue, s);
+    os << "  {\n    \"name\": ";
+    wpi::util::json::stringify_string(os, topic->name);
+    os << ",\n    \"type\": ";
+    wpi::util::json::stringify_string(os, topic->typeStr);
+    os << ",\n    \"value\": ";
+    DumpValue(os, topic->lastValue);
     os << ",\n    \"properties\": ";
-    s.dump(topic->properties, true, false, 2, 4);
+    topic->properties.marshal(os, true, 2);
     os << "\n  }";
   }
   os << "\n]\n";
 }
 
-static std::string* ObjGetString(wpi::util::json::object_t& obj,
-                                 std::string_view key, std::string* error) {
-  auto it = obj.find(key);
-  if (it == obj.end()) {
+static std::string* ObjGetString(wpi::util::json& obj, std::string_view key,
+                                 std::string* error) {
+  auto value = obj.lookup(key);
+  if (!value) {
     *error = fmt::format("no {} key", key);
     return nullptr;
   }
-  auto val = it->second.get_ptr<std::string*>();
-  if (!val) {
+  if (!value->is_string()) {
     *error = fmt::format("{} must be a string", key);
+    return nullptr;
   }
-  return val;
+  return &value->get_string();
 }
 
 std::string ServerStorage::LoadPersistent(std::string_view in) {
@@ -391,14 +381,12 @@ std::string ServerStorage::LoadPersistent(std::string_view in) {
     return {};
   }
 
-  wpi::util::json j;
-  try {
-    j = wpi::util::json::parse(in);
-  } catch (wpi::util::json::parse_error& err) {
-    return fmt::format("could not decode JSON: {}", err.what());
+  auto j = wpi::util::json::parse(in);
+  if (!j) {
+    return fmt::format("could not decode JSON: {}", j.error());
   }
 
-  if (!j.is_array()) {
+  if (!j->is_array()) {
     return "expected JSON array at top level";
   }
 
@@ -407,48 +395,46 @@ std::string ServerStorage::LoadPersistent(std::string_view in) {
   std::string allerrors;
   int i = -1;
   auto time = wpi::nt::Now();
-  for (auto&& jitem : j) {
+  for (auto&& jitem : j->get_array()) {
     ++i;
     std::string error;
     {
-      auto obj = jitem.get_ptr<wpi::util::json::object_t*>();
-      if (!obj) {
+      if (!jitem.is_object()) {
         error = "expected item to be an object";
         goto err;
       }
 
       // name
-      auto name = ObjGetString(*obj, "name", &error);
+      auto name = ObjGetString(jitem, "name", &error);
       if (!name) {
         goto err;
       }
 
       // type
-      auto typeStr = ObjGetString(*obj, "type", &error);
+      auto typeStr = ObjGetString(jitem, "type", &error);
       if (!typeStr) {
         goto err;
       }
 
       // properties
-      auto propsIt = obj->find("properties");
-      if (propsIt == obj->end()) {
+      auto props = jitem.lookup("properties");
+      if (!props) {
         error = "no properties key";
         goto err;
       }
-      auto& props = propsIt->second;
-      if (!props.is_object()) {
+      if (!props->is_object()) {
         error = "properties must be an object";
         goto err;
       }
 
       // check to make sure persistent property is set
-      auto persistentIt = props.find("persistent");
-      if (persistentIt == props.end()) {
+      auto persistent = props->lookup("persistent");
+      if (!persistent) {
         error = "no persistent property";
         goto err;
       }
-      if (auto v = persistentIt->get_ptr<bool*>()) {
-        if (!*v) {
+      if (persistent->is_bool()) {
+        if (!persistent->get_bool()) {
           error = "persistent property is false";
           goto err;
         }
@@ -458,121 +444,112 @@ std::string ServerStorage::LoadPersistent(std::string_view in) {
       }
 
       // value
-      auto valueIt = obj->find("value");
-      if (valueIt == obj->end()) {
+      auto jvalue = jitem.lookup("value");
+      if (!jvalue) {
         error = "no value key";
         goto err;
       }
       Value value;
       if (*typeStr == "boolean") {
-        if (auto v = valueIt->second.get_ptr<bool*>()) {
-          value = Value::MakeBoolean(*v, time);
+        if (jvalue->is_bool()) {
+          value = Value::MakeBoolean(jvalue->get_bool(), time);
         } else {
           error = "value type mismatch, expected boolean";
           goto err;
         }
       } else if (*typeStr == "int") {
-        if (auto v = valueIt->second.get_ptr<int64_t*>()) {
-          value = Value::MakeInteger(*v, time);
-        } else if (auto v = valueIt->second.get_ptr<uint64_t*>()) {
-          value = Value::MakeInteger(*v, time);
+        if (jvalue->is_int()) {
+          value = Value::MakeInteger(jvalue->get_int(), time);
         } else {
           error = "value type mismatch, expected int";
           goto err;
         }
       } else if (*typeStr == "float") {
-        if (auto v = valueIt->second.get_ptr<double*>()) {
-          value = Value::MakeFloat(*v, time);
+        if (jvalue->is_number()) {
+          value = Value::MakeFloat(jvalue->get_number(), time);
         } else {
           error = "value type mismatch, expected float";
           goto err;
         }
       } else if (*typeStr == "double") {
-        if (auto v = valueIt->second.get_ptr<double*>()) {
-          value = Value::MakeDouble(*v, time);
+        if (jvalue->is_number()) {
+          value = Value::MakeDouble(jvalue->get_number(), time);
         } else {
           error = "value type mismatch, expected double";
           goto err;
         }
       } else if (*typeStr == "string" || *typeStr == "json") {
-        if (auto v = valueIt->second.get_ptr<std::string*>()) {
-          value = Value::MakeString(*v, time);
+        if (jvalue->is_string()) {
+          value = Value::MakeString(jvalue->get_string(), time);
         } else {
           error = "value type mismatch, expected string";
           goto err;
         }
       } else if (*typeStr == "boolean[]") {
-        auto arr = valueIt->second.get_ptr<wpi::util::json::array_t*>();
-        if (!arr) {
+        if (!jvalue->is_array()) {
           error = "value type mismatch, expected array";
           goto err;
         }
         std::vector<int> elems;
-        for (auto&& jelem : valueIt->second) {
-          if (auto v = jelem.get_ptr<bool*>()) {
-            elems.push_back(*v);
+        for (auto&& jelem : jvalue->get_array()) {
+          if (jelem.is_bool()) {
+            elems.push_back(jelem.get_bool());
           } else {
             error = "value type mismatch, expected boolean";
           }
         }
         value = Value::MakeBooleanArray(elems, time);
       } else if (*typeStr == "int[]") {
-        auto arr = valueIt->second.get_ptr<wpi::util::json::array_t*>();
-        if (!arr) {
+        if (!jvalue->is_array()) {
           error = "value type mismatch, expected array";
           goto err;
         }
         std::vector<int64_t> elems;
-        for (auto&& jelem : valueIt->second) {
-          if (auto v = jelem.get_ptr<int64_t*>()) {
-            elems.push_back(*v);
-          } else if (auto v = jelem.get_ptr<uint64_t*>()) {
-            elems.push_back(*v);
+        for (auto&& jelem : jvalue->get_array()) {
+          if (jelem.is_int()) {
+            elems.push_back(jelem.get_int());
           } else {
             error = "value type mismatch, expected int";
           }
         }
         value = Value::MakeIntegerArray(elems, time);
       } else if (*typeStr == "double[]") {
-        auto arr = valueIt->second.get_ptr<wpi::util::json::array_t*>();
-        if (!arr) {
+        if (!jvalue->is_array()) {
           error = "value type mismatch, expected array";
           goto err;
         }
         std::vector<double> elems;
-        for (auto&& jelem : valueIt->second) {
-          if (auto v = jelem.get_ptr<double*>()) {
-            elems.push_back(*v);
+        for (auto&& jelem : jvalue->get_array()) {
+          if (jelem.is_number()) {
+            elems.push_back(jelem.get_number());
           } else {
             error = "value type mismatch, expected double";
           }
         }
         value = Value::MakeDoubleArray(elems, time);
       } else if (*typeStr == "float[]") {
-        auto arr = valueIt->second.get_ptr<wpi::util::json::array_t*>();
-        if (!arr) {
+        if (!jvalue->is_array()) {
           error = "value type mismatch, expected array";
           goto err;
         }
         std::vector<float> elems;
-        for (auto&& jelem : valueIt->second) {
-          if (auto v = jelem.get_ptr<double*>()) {
-            elems.push_back(*v);
+        for (auto&& jelem : jvalue->get_array()) {
+          if (jelem.is_number()) {
+            elems.push_back(jelem.get_number());
           } else {
             error = "value type mismatch, expected float";
           }
         }
         value = Value::MakeFloatArray(elems, time);
       } else if (*typeStr == "string[]") {
-        auto arr = valueIt->second.get_ptr<wpi::util::json::array_t*>();
-        if (!arr) {
+        if (!jvalue->is_array()) {
           error = "value type mismatch, expected array";
           goto err;
         }
         std::vector<std::string> elems;
-        for (auto&& jelem : valueIt->second) {
-          if (auto v = jelem.get_ptr<std::string*>()) {
-            elems.emplace_back(*v);
+        for (auto&& jelem : jvalue->get_array()) {
+          if (jelem.is_string()) {
+            elems.push_back(jelem.get_string());
           } else {
             error = "value type mismatch, expected string";
           }
@@ -580,9 +557,9 @@ std::string ServerStorage::LoadPersistent(std::string_view in) {
         value = Value::MakeStringArray(std::move(elems), time);
       } else {
         // raw
-        if (auto v = valueIt->second.get_ptr<std::string*>()) {
+        if (jvalue->is_string()) {
           std::vector<uint8_t> data;
-          wpi::util::Base64Decode(*v, &data);
+          wpi::util::Base64Decode(jvalue->get_string(), &data);
           value = Value::MakeRaw(std::move(data), time);
         } else {
           error = "value type mismatch, expected string";
@@ -591,7 +568,7 @@ std::string ServerStorage::LoadPersistent(std::string_view in) {
       }
 
       // create persistent topic
-      auto topic = CreateTopic(nullptr, *name, *typeStr, props);
+      auto topic = CreateTopic(nullptr, *name, *typeStr, *props);
 
       // set value
       SetValue(nullptr, topic, value);
diff --git a/ntcore/src/main/native/cpp/server/ServerStorage.hpp b/ntcore/src/main/native/cpp/server/ServerStorage.hpp
index 3c5756b4ef..e4c9e886e5 100644
--- a/ntcore/src/main/native/cpp/server/ServerStorage.hpp
+++ b/ntcore/src/main/native/cpp/server/ServerStorage.hpp
@@ -12,10 +12,10 @@
 #include "server/ServerTopic.hpp"
 #include "wpi/util/StringMap.hpp"
 #include "wpi/util/UidVector.hpp"
-#include "wpi/util/json_fwd.hpp"
 
 namespace wpi::util {
 class Logger;
+class json;
 class raw_ostream;
 }  // namespace wpi::util
 
diff --git a/ntcore/src/main/native/cpp/server/ServerTopic.cpp b/ntcore/src/main/native/cpp/server/ServerTopic.cpp
index eaf85ddd76..a036b6f048 100644
--- a/ntcore/src/main/native/cpp/server/ServerTopic.cpp
+++ b/ntcore/src/main/native/cpp/server/ServerTopic.cpp
@@ -13,11 +13,11 @@ bool ServerTopic::SetProperties(const wpi::util::json& update) {
     return false;
   }
   bool updated = false;
-  for (auto&& elem : update.items()) {
-    if (elem.value().is_null()) {
-      properties.erase(elem.key());
+  for (auto&& [key, value] : update.get_object()) {
+    if (value.is_null()) {
+      properties.erase(key);
     } else {
-      properties[elem.key()] = elem.value();
+      properties[key] = value;
     }
     updated = true;
   }
@@ -32,24 +32,21 @@ void ServerTopic::RefreshProperties() {
   retained = false;
   cached = true;
 
-  auto persistentIt = properties.find("persistent");
-  if (persistentIt != properties.end()) {
-    if (auto val = persistentIt->get_ptr<bool*>()) {
-      persistent = *val;
+  if (auto prop = properties.lookup("persistent")) {
+    if (prop->is_bool()) {
+      persistent = prop->get_bool();
     }
   }
 
-  auto retainedIt = properties.find("retained");
-  if (retainedIt != properties.end()) {
-    if (auto val = retainedIt->get_ptr<bool*>()) {
-      retained = *val;
+  if (auto prop = properties.lookup("retained")) {
+    if (prop->is_bool()) {
+      retained = prop->get_bool();
     }
   }
 
-  auto cachedIt = properties.find("cached");
-  if (cachedIt != properties.end()) {
-    if (auto val = cachedIt->get_ptr<bool*>()) {
-      cached = *val;
+  if (auto prop = properties.lookup("cached")) {
+    if (prop->is_bool()) {
+      cached = prop->get_bool();
     }
   }
 
diff --git a/ntcore/src/main/native/include/wpi/nt/ProtobufTopic.hpp b/ntcore/src/main/native/include/wpi/nt/ProtobufTopic.hpp
index b4020f0cd9..e449447387 100644
--- a/ntcore/src/main/native/include/wpi/nt/ProtobufTopic.hpp
+++ b/ntcore/src/main/native/include/wpi/nt/ProtobufTopic.hpp
@@ -15,10 +15,13 @@
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
 #include "wpi/util/SmallVector.hpp"
-#include "wpi/util/json_fwd.hpp"
 #include "wpi/util/mutex.hpp"
 #include "wpi/util/protobuf/Protobuf.hpp"
 
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
+
 namespace wpi::nt {
 
 template <wpi::util::ProtobufSerializable T>
diff --git a/ntcore/src/main/native/include/wpi/nt/StructArrayTopic.hpp b/ntcore/src/main/native/include/wpi/nt/StructArrayTopic.hpp
index 62013b8fd4..18646b9aca 100644
--- a/ntcore/src/main/native/include/wpi/nt/StructArrayTopic.hpp
+++ b/ntcore/src/main/native/include/wpi/nt/StructArrayTopic.hpp
@@ -19,10 +19,13 @@
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
 #include "wpi/util/SmallVector.hpp"
-#include "wpi/util/json_fwd.hpp"
 #include "wpi/util/mutex.hpp"
 #include "wpi/util/struct/Struct.hpp"
 
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
+
 namespace wpi::nt {
 
 template <typename T, typename... I>
diff --git a/ntcore/src/main/native/include/wpi/nt/StructTopic.hpp b/ntcore/src/main/native/include/wpi/nt/StructTopic.hpp
index f910c3c334..4ddae2c280 100644
--- a/ntcore/src/main/native/include/wpi/nt/StructTopic.hpp
+++ b/ntcore/src/main/native/include/wpi/nt/StructTopic.hpp
@@ -19,9 +19,12 @@
 #include "wpi/nt/Topic.hpp"
 #include "wpi/nt/ntcore_cpp.hpp"
 #include "wpi/util/SmallVector.hpp"
-#include "wpi/util/json_fwd.hpp"
 #include "wpi/util/struct/Struct.hpp"
 
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
+
 namespace wpi::nt {
 
 template <typename T, typename... I>
diff --git a/ntcore/src/main/native/include/wpi/nt/Topic.hpp b/ntcore/src/main/native/include/wpi/nt/Topic.hpp
index edab600d2c..7fe5b0e046 100644
--- a/ntcore/src/main/native/include/wpi/nt/Topic.hpp
+++ b/ntcore/src/main/native/include/wpi/nt/Topic.hpp
@@ -14,7 +14,10 @@
 #include "wpi/nt/NetworkTableType.hpp"
 #include "wpi/nt/ntcore_c.h"
 #include "wpi/nt/ntcore_cpp.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::nt {
 
diff --git a/ntcore/src/main/native/include/wpi/nt/UnitTopic.hpp b/ntcore/src/main/native/include/wpi/nt/UnitTopic.hpp
index 2cd1c0f188..fabbdb5ad3 100644
--- a/ntcore/src/main/native/include/wpi/nt/UnitTopic.hpp
+++ b/ntcore/src/main/native/include/wpi/nt/UnitTopic.hpp
@@ -369,7 +369,8 @@ class UnitTopic final : public Topic {
   PublisherType Publish(
       const PubSubOptions& options = DEFAULT_PUB_SUB_OPTIONS) {
     return UnitPublisher<T>{::wpi::nt::PublishEx(
-        m_handle, NT_DOUBLE, "double", {{"unit", T{}.name()}}, options)};
+        m_handle, NT_DOUBLE, "double",
+        wpi::util::json::object("unit", T{}.name()), options)};
   }
 
   /**
diff --git a/ntcore/src/main/native/include/wpi/nt/ntcore_cpp.hpp b/ntcore/src/main/native/include/wpi/nt/ntcore_cpp.hpp
index e5b58deb85..5d80bfca53 100644
--- a/ntcore/src/main/native/include/wpi/nt/ntcore_cpp.hpp
+++ b/ntcore/src/main/native/include/wpi/nt/ntcore_cpp.hpp
@@ -19,9 +19,9 @@
 #include "wpi/nt/NetworkTableValue.hpp"
 #include "wpi/nt/ntcore_c.h"
 #include "wpi/nt/ntcore_cpp_types.hpp"
-#include "wpi/util/json_fwd.hpp"
 
 namespace wpi::util {
+class json;
 template <typename T>
 class SmallVectorImpl;
 }  // namespace wpi::util
diff --git a/ntcore/src/test/native/cpp/LocalStorageTest.cpp b/ntcore/src/test/native/cpp/LocalStorageTest.cpp
index 6e81a8549a..95d35101f1 100644
--- a/ntcore/src/test/native/cpp/LocalStorageTest.cpp
+++ b/ntcore/src/test/native/cpp/LocalStorageTest.cpp
@@ -144,11 +144,12 @@ TEST_F(LocalStorageTest, PublishNewNoPropsNull) {
 }
 
 TEST_F(LocalStorageTest, PublishNew) {
-  wpi::util::json properties = {{"persistent", true}};
+  auto properties = wpi::util::json::object("persistent", true);
   EXPECT_CALL(network, ClientPublish(_, std::string_view{"foo"},
                                      std::string_view{"boolean"}, properties,
                                      IsDefaultPubSubOptions()));
-  storage.Publish(fooTopic, NT_BOOLEAN, "boolean", {{"persistent", true}}, {});
+  storage.Publish(fooTopic, NT_BOOLEAN, "boolean",
+                  wpi::util::json::object("persistent", true), {});
 
   auto info = storage.GetTopicInfo(fooTopic);
   EXPECT_EQ(info.topic, fooTopic);
@@ -645,7 +646,8 @@ TEST_F(LocalStorageDuplicatesTest, FromNetworkDefault) {
   SetupPubSub(false, false);
 
   // incoming from the network are treated like a normal local publish
-  auto topic = storage.ServerAnnounce("foo", 0, "double", {{}}, std::nullopt);
+  auto topic = storage.ServerAnnounce("foo", 0, "double",
+                                      wpi::util::json::object(), std::nullopt);
   storage.ServerSetValue(topic, val1);
   storage.ServerSetValue(topic, val2);
   // verify the timestamp was updated
@@ -665,7 +667,8 @@ TEST_F(LocalStorageDuplicatesTest, FromNetworkKeepPub) {
   SetupPubSub(true, false);
 
   // incoming from the network are treated like a normal local publish
-  auto topic = storage.ServerAnnounce("foo", 0, "double", {{}}, std::nullopt);
+  auto topic = storage.ServerAnnounce("foo", 0, "double",
+                                      wpi::util::json::object(), std::nullopt);
   storage.ServerSetValue(topic, val1);
   storage.ServerSetValue(topic, val2);
   // verify the timestamp was updated
@@ -684,7 +687,8 @@ TEST_F(LocalStorageDuplicatesTest, FromNetworkKeepSub) {
   SetupPubSub(false, true);
 
   // incoming from the network are treated like a normal local publish
-  auto topic = storage.ServerAnnounce("foo", 0, "double", {{}}, std::nullopt);
+  auto topic = storage.ServerAnnounce("foo", 0, "double",
+                                      wpi::util::json::object(), std::nullopt);
   storage.ServerSetValue(topic, val1);
   storage.ServerSetValue(topic, val2);
   // verify the timestamp was updated
@@ -706,7 +710,8 @@ TEST_F(LocalStorageDuplicatesTest, FromNetworkKeepPubSub) {
   SetupPubSub(true, true);
 
   // incoming from the network are treated like a normal local publish
-  auto topic = storage.ServerAnnounce("foo", 0, "double", {{}}, std::nullopt);
+  auto topic = storage.ServerAnnounce("foo", 0, "double",
+                                      wpi::util::json::object(), std::nullopt);
   storage.ServerSetValue(topic, val1);
   storage.ServerSetValue(topic, val2);
   // verify the timestamp was updated
diff --git a/ntcore/src/test/native/cpp/StructTest.cpp b/ntcore/src/test/native/cpp/StructTest.cpp
index 82d66e40c9..33304556a7 100644
--- a/ntcore/src/test/native/cpp/StructTest.cpp
+++ b/ntcore/src/test/native/cpp/StructTest.cpp
@@ -342,7 +342,8 @@ TEST_F(StructTest, InnerArrayNonconstexpr) {
 TEST_F(StructTest, StructA) {
   wpi::nt::StructTopic<ThingA> topic = inst.GetStructTopic<ThingA>("a");
   wpi::nt::StructPublisher<ThingA> pub = topic.Publish();
-  wpi::nt::StructPublisher<ThingA> pub2 = topic.PublishEx({{}});
+  wpi::nt::StructPublisher<ThingA> pub2 =
+      topic.PublishEx(wpi::util::json::object());
   wpi::nt::StructSubscriber<ThingA> sub = topic.Subscribe({});
   wpi::nt::StructEntry<ThingA> entry = topic.GetEntry({});
   pub.SetDefault({});
@@ -360,7 +361,8 @@ TEST_F(StructTest, StructArrayA) {
   wpi::nt::StructArrayTopic<ThingA> topic =
       inst.GetStructArrayTopic<ThingA>("a");
   wpi::nt::StructArrayPublisher<ThingA> pub = topic.Publish();
-  wpi::nt::StructArrayPublisher<ThingA> pub2 = topic.PublishEx({{}});
+  wpi::nt::StructArrayPublisher<ThingA> pub2 =
+      topic.PublishEx(wpi::util::json::object());
   wpi::nt::StructArraySubscriber<ThingA> sub = topic.Subscribe({});
   wpi::nt::StructArrayEntry<ThingA> entry = topic.GetEntry({});
   pub.SetDefault({{ThingA{}, ThingA{}}});
@@ -378,7 +380,8 @@ TEST_F(StructTest, StructFixedArrayA) {
   wpi::nt::StructTopic<std::array<ThingA, 2>> topic =
       inst.GetStructTopic<std::array<ThingA, 2>>("a");
   wpi::nt::StructPublisher<std::array<ThingA, 2>> pub = topic.Publish();
-  wpi::nt::StructPublisher<std::array<ThingA, 2>> pub2 = topic.PublishEx({{}});
+  wpi::nt::StructPublisher<std::array<ThingA, 2>> pub2 =
+      topic.PublishEx(wpi::util::json::object());
   wpi::nt::StructSubscriber<std::array<ThingA, 2>> sub = topic.Subscribe({});
   wpi::nt::StructEntry<std::array<ThingA, 2>> entry = topic.GetEntry({});
   std::array<ThingA, 2> arr;
@@ -398,7 +401,8 @@ TEST_F(StructTest, StructB) {
   wpi::nt::StructTopic<ThingB, Info1> topic =
       inst.GetStructTopic<ThingB, Info1>("b", info);
   wpi::nt::StructPublisher<ThingB, Info1> pub = topic.Publish();
-  wpi::nt::StructPublisher<ThingB, Info1> pub2 = topic.PublishEx({{}});
+  wpi::nt::StructPublisher<ThingB, Info1> pub2 =
+      topic.PublishEx(wpi::util::json::object());
   wpi::nt::StructSubscriber<ThingB, Info1> sub = topic.Subscribe({});
   wpi::nt::StructEntry<ThingB, Info1> entry = topic.GetEntry({});
   pub.SetDefault({});
@@ -417,7 +421,8 @@ TEST_F(StructTest, StructArrayB) {
   wpi::nt::StructArrayTopic<ThingB, Info1> topic =
       inst.GetStructArrayTopic<ThingB, Info1>("b", info);
   wpi::nt::StructArrayPublisher<ThingB, Info1> pub = topic.Publish();
-  wpi::nt::StructArrayPublisher<ThingB, Info1> pub2 = topic.PublishEx({{}});
+  wpi::nt::StructArrayPublisher<ThingB, Info1> pub2 =
+      topic.PublishEx(wpi::util::json::object());
   wpi::nt::StructArraySubscriber<ThingB, Info1> sub = topic.Subscribe({});
   wpi::nt::StructArrayEntry<ThingB, Info1> entry = topic.GetEntry({});
   pub.SetDefault({{ThingB{}, ThingB{}}});
@@ -437,7 +442,7 @@ TEST_F(StructTest, StructFixedArrayB) {
       inst.GetStructTopic<std::array<ThingB, 2>, Info1>("b", info);
   wpi::nt::StructPublisher<std::array<ThingB, 2>, Info1> pub = topic.Publish();
   wpi::nt::StructPublisher<std::array<ThingB, 2>, Info1> pub2 =
-      topic.PublishEx({{}});
+      topic.PublishEx(wpi::util::json::object());
   wpi::nt::StructSubscriber<std::array<ThingB, 2>, Info1> sub =
       topic.Subscribe({});
   wpi::nt::StructEntry<std::array<ThingB, 2>, Info1> entry = topic.GetEntry({});
diff --git a/ntcore/src/test/native/cpp/net/WireDecoderTest.cpp b/ntcore/src/test/native/cpp/net/WireDecoderTest.cpp
index 517eaa1839..b71e6d4c52 100644
--- a/ntcore/src/test/native/cpp/net/WireDecoderTest.cpp
+++ b/ntcore/src/test/native/cpp/net/WireDecoderTest.cpp
@@ -43,33 +43,20 @@ TEST_F(WireDecodeTextClientTest, EmptyArray) {
 }
 
 TEST_F(WireDecodeTextClientTest, ErrorEmpty) {
-  EXPECT_CALL(
-      logger,
-      Call(_, _, _,
-           "could not decode JSON message: [json.exception.parse_error.101] "
-           "parse error at line 1, column 1: attempting to parse an empty "
-           "input; check that your input string or stream contains the "
-           "expected JSON"sv));
+  EXPECT_CALL(logger,
+              Call(_, _, _, "could not decode JSON message: absent_value"sv));
   net::WireDecodeText("", handler, logger);
 }
 
 TEST_F(WireDecodeTextClientTest, ErrorBadJson1) {
-  EXPECT_CALL(
-      logger,
-      Call(_, _, _,
-           "could not decode JSON message: [json.exception.parse_error.101] "
-           "parse error at line 1, column 2: syntax error while parsing value "
-           "- unexpected end of input; expected '[', '{', or a literal"sv));
+  EXPECT_CALL(logger,
+              Call(_, _, _, "could not decode JSON message: unexpected_eof"sv));
   net::WireDecodeText("[", handler, logger);
 }
 
 TEST_F(WireDecodeTextClientTest, ErrorBadJson2) {
-  EXPECT_CALL(
-      logger,
-      Call(_, _, _,
-           "could not decode JSON message: [json.exception.parse_error.101] "
-           "parse error at line 1, column 3: syntax error while parsing object "
-           "key - unexpected end of input; expected string literal"sv));
+  EXPECT_CALL(logger,
+              Call(_, _, _, "could not decode JSON message: unexpected_eof"sv));
   net::WireDecodeText("[{", handler, logger);
 }
 
@@ -129,7 +116,7 @@ TEST_F(WireDecodeTextClientTest, PublishPropsEmpty) {
 }
 
 TEST_F(WireDecodeTextClientTest, PublishProps) {
-  wpi::util::json props = {{"k", 6}};
+  auto props = wpi::util::json::object("k", 6);
   EXPECT_CALL(handler, ClientPublish(5, std::string_view{"test"},
                                      std::string_view{"double"}, props,
                                      PubSubOptionsEq({})));
diff --git a/ntcore/src/test/native/cpp/net/WireEncoderTest.cpp b/ntcore/src/test/native/cpp/net/WireEncoderTest.cpp
index e8bdf9134e..a80cafb5cb 100644
--- a/ntcore/src/test/native/cpp/net/WireEncoderTest.cpp
+++ b/ntcore/src/test/native/cpp/net/WireEncoderTest.cpp
@@ -29,7 +29,9 @@ class WireEncoderTextTest : public ::testing::Test {
  protected:
   std::string out;
   wpi::util::raw_string_ostream os{out};
-  wpi::util::json GetJson() { return wpi::util::json::parse(os.str()); }
+  wpi::util::json GetJson() {
+    return wpi::util::json::parse(os.str()).value_or(wpi::util::json::object());
+  }
 };
 
 class WireEncoderBinaryTest : public ::testing::Test {
@@ -47,7 +49,8 @@ TEST_F(WireEncoderTextTest, PublishPropsEmpty) {
 }
 
 TEST_F(WireEncoderTextTest, PublishProps) {
-  net::WireEncodePublish(os, 5, "test", "double", {{"k", 6}});
+  net::WireEncodePublish(os, 5, "test", "double",
+                         wpi::util::json::object("k", 6));
   ASSERT_EQ(os.str(),
             "{\"method\":\"publish\",\"params\":{"
             "\"name\":\"test\",\"properties\":{\"k\":6},"
@@ -60,7 +63,7 @@ TEST_F(WireEncoderTextTest, Unpublish) {
 }
 
 TEST_F(WireEncoderTextTest, SetProperties) {
-  net::WireEncodeSetProperties(os, "test", {{"k", 6}});
+  net::WireEncodeSetProperties(os, "test", wpi::util::json::object("k", 6));
   ASSERT_EQ(os.str(),
             "{\"method\":\"setproperties\",\"params\":{"
             "\"name\":\"test\",\"update\":{\"k\":6}}}");
@@ -122,7 +125,8 @@ TEST_F(WireEncoderTextTest, Announce) {
 }
 
 TEST_F(WireEncoderTextTest, AnnounceProperties) {
-  net::WireEncodeAnnounce(os, "test", 5, "double", {{"k", 6}}, std::nullopt);
+  net::WireEncodeAnnounce(os, "test", 5, "double",
+                          wpi::util::json::object("k", 6), std::nullopt);
   ASSERT_EQ(os.str(),
             "{\"method\":\"announce\",\"params\":{\"id\":5,\"name\":\"test\","
             "\"properties\":{\"k\":6},\"type\":\"double\"}}");
@@ -144,7 +148,8 @@ TEST_F(WireEncoderTextTest, Unannounce) {
 }
 
 TEST_F(WireEncoderTextTest, MessagePublish) {
-  net::ClientMessage msg{net::PublishMsg{5, "test", "double", {{"k", 6}}, {}}};
+  net::ClientMessage msg{net::PublishMsg{
+      5, "test", "double", wpi::util::json::object("k", 6), {}}};
   ASSERT_TRUE(net::WireEncodeText(os, msg));
   ASSERT_EQ(os.str(),
             "{\"method\":\"publish\",\"params\":{"
@@ -159,7 +164,8 @@ TEST_F(WireEncoderTextTest, MessageUnpublish) {
 }
 
 TEST_F(WireEncoderTextTest, MessageSetProperties) {
-  net::ClientMessage msg{net::SetPropertiesMsg{"test", {{"k", 6}}}};
+  net::ClientMessage msg{
+      net::SetPropertiesMsg{"test", wpi::util::json::object("k", 6)}};
   ASSERT_TRUE(net::WireEncodeText(os, msg));
   ASSERT_EQ(os.str(),
             "{\"method\":\"setproperties\",\"params\":{"
@@ -190,8 +196,8 @@ TEST_F(WireEncoderTextTest, MessageAnnounce) {
 }
 
 TEST_F(WireEncoderTextTest, MessageAnnounceProperties) {
-  net::ServerMessage msg{
-      net::AnnounceMsg{"test", 5, "double", std::nullopt, {{"k", 6}}}};
+  net::ServerMessage msg{net::AnnounceMsg{"test", 5, "double", std::nullopt,
+                                          wpi::util::json::object("k", 6)}};
   ASSERT_TRUE(net::WireEncodeText(os, msg));
   ASSERT_EQ(os.str(),
             "{\"method\":\"announce\",\"params\":{\"id\":5,\"name\":\"test\","
diff --git a/simulation/halsim_ws_client/src/main/native/cpp/HALSimWS.cpp b/simulation/halsim_ws_client/src/main/native/cpp/HALSimWS.cpp
index 2e685b622d..975ba4298a 100644
--- a/simulation/halsim_ws_client/src/main/native/cpp/HALSimWS.cpp
+++ b/simulation/halsim_ws_client/src/main/native/cpp/HALSimWS.cpp
@@ -177,8 +177,8 @@ void HALSimWS::OnNetValueChanged(const wpi::util::json& msg) {
   // generate the key
 
   try {
-    auto& type = msg.at("type").get_ref<const std::string&>();
-    auto& device = msg.at("device").get_ref<const std::string&>();
+    auto& type = msg.at("type").get_string();
+    auto& device = msg.at("device").get_string();
 
     wpi::util::SmallString<64> key;
     key.append(type);
@@ -191,7 +191,7 @@ void HALSimWS::OnNetValueChanged(const wpi::util::json& msg) {
     if (provider) {
       provider->OnNetValueChanged(msg.at("data"));
     }
-  } catch (wpi::util::json::exception& e) {
+  } catch (std::logic_error& e) {
     wpi::util::print(stderr, "Error with incoming message: {}\n", e.what());
   }
 }
diff --git a/simulation/halsim_ws_client/src/main/native/cpp/HALSimWSClientConnection.cpp b/simulation/halsim_ws_client/src/main/native/cpp/HALSimWSClientConnection.cpp
index 57bd42f0d8..41c4e8b4e9 100644
--- a/simulation/halsim_ws_client/src/main/native/cpp/HALSimWSClientConnection.cpp
+++ b/simulation/halsim_ws_client/src/main/native/cpp/HALSimWSClientConnection.cpp
@@ -48,18 +48,15 @@ void HALSimWSClientConnection::Initialize() {
       return;
     }
 
-    wpi::util::json j;
-    try {
-      j = wpi::util::json::parse(msg);
-    } catch (const wpi::util::json::parse_error& e) {
-      std::string err("JSON parse failed: ");
-      err += e.what();
+    auto j = wpi::util::json::parse(msg);
+    if (!j) {
+      auto err = fmt::format("JSON parse failed: {}", j.error());
       wpi::util::print(stderr, "{}\n", err);
       m_websocket->Fail(1003, err);
       return;
     }
 
-    m_client->OnNetValueChanged(j);
+    m_client->OnNetValueChanged(*j);
   });
 
   m_websocket->closed.connect([this](uint16_t, auto) {
@@ -79,11 +76,11 @@ void HALSimWSClientConnection::OnSimValueChanged(const wpi::util::json& msg) {
 
   // Skip sending if this message is not in the allowed filter list
   try {
-    auto& type = msg.at("type").get_ref<const std::string&>();
+    auto& type = msg.at("type").get_string();
     if (!m_client->CanSendMessage(type)) {
       return;
     }
-  } catch (wpi::util::json::exception& e) {
+  } catch (std::logic_error& e) {
     wpi::util::print(stderr, "Error with message: {}\n", e.what());
   }
 
diff --git a/simulation/halsim_ws_client/src/main/native/include/wpi/halsim/ws_client/HALSimWS.hpp b/simulation/halsim_ws_client/src/main/native/include/wpi/halsim/ws_client/HALSimWS.hpp
index ca8ec6df2a..c00e12ea59 100644
--- a/simulation/halsim_ws_client/src/main/native/include/wpi/halsim/ws_client/HALSimWS.hpp
+++ b/simulation/halsim_ws_client/src/main/native/include/wpi/halsim/ws_client/HALSimWS.hpp
@@ -16,7 +16,10 @@
 #include "wpi/net/uv/Tcp.hpp"
 #include "wpi/net/uv/Timer.hpp"
 #include "wpi/util/StringMap.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpilibws {
 
diff --git a/simulation/halsim_ws_client/src/main/native/include/wpi/halsim/ws_client/HALSimWSClientConnection.hpp b/simulation/halsim_ws_client/src/main/native/include/wpi/halsim/ws_client/HALSimWSClientConnection.hpp
index 25cde92214..79e9ec21cb 100644
--- a/simulation/halsim_ws_client/src/main/native/include/wpi/halsim/ws_client/HALSimWSClientConnection.hpp
+++ b/simulation/halsim_ws_client/src/main/native/include/wpi/halsim/ws_client/HALSimWSClientConnection.hpp
@@ -12,8 +12,10 @@
 #include "wpi/net/WebSocket.hpp"
 #include "wpi/net/uv/Buffer.hpp"
 #include "wpi/net/uv/Stream.hpp"
-#include "wpi/util/json_fwd.hpp"
-#include "wpi/util/mutex.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpilibws {
 
diff --git a/simulation/halsim_ws_core/src/main/native/cpp/WSHalProviders.cpp b/simulation/halsim_ws_core/src/main/native/cpp/WSHalProviders.cpp
index bd8b83dfa5..b39957307f 100644
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSHalProviders.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSHalProviders.cpp
@@ -27,8 +27,10 @@ void HALSimWSHalProvider::OnNetworkDisconnected() {
 void HALSimWSHalProvider::ProcessHalCallback(const wpi::util::json& payload) {
   auto ws = m_ws.lock();
   if (ws) {
-    wpi::util::json netValue = {
-        {"type", m_type}, {"device", m_deviceId}, {"data", payload}};
+    auto netValue = wpi::util::json::object();
+    netValue["type"] = m_type;
+    netValue["device"] = m_deviceId;
+    netValue["data"] = payload;
     ws->OnSimValueChanged(netValue);
   }
 }
diff --git a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_AddressableLED.cpp b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_AddressableLED.cpp
index 4b4baa80bb..caa35f67b3 100644
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_AddressableLED.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_AddressableLED.cpp
@@ -4,19 +4,20 @@
 
 #include "wpi/halsim/ws_core/WSProvider_AddressableLED.hpp"
 
+#include <utility>
 #include <vector>
 
 #include "wpi/hal/Ports.h"
 #include "wpi/hal/simulation/AddressableLEDData.h"
 
-#define REGISTER(halsim, jsonid, ctype, haltype)                          \
-  HALSIM_RegisterAddressableLED##halsim##Callback(                        \
-      m_channel,                                                          \
-      [](const char* name, void* param, const struct HAL_Value* value) {  \
-        static_cast<HALSimWSProviderAddressableLED*>(param)               \
-            ->ProcessHalCallback(                                         \
-                {{jsonid, static_cast<ctype>(value->data.v_##haltype)}}); \
-      },                                                                  \
+#define REGISTER(halsim, jsonid, ctype, haltype)                         \
+  HALSIM_RegisterAddressableLED##halsim##Callback(                       \
+      m_channel,                                                         \
+      [](const char* name, void* param, const struct HAL_Value* value) { \
+        static_cast<HALSimWSProviderAddressableLED*>(param)              \
+            ->ProcessHalCallback(wpi::util::json::object(                \
+                jsonid, static_cast<ctype>(value->data.v_##haltype)));   \
+      },                                                                 \
       this, true)
 namespace wpilibws {
 void HALSimWSProviderAddressableLED::Initialize(
@@ -43,15 +44,17 @@ void HALSimWSProviderAddressableLED::RegisterCallbacks() {
         const HAL_AddressableLEDData* data =
             reinterpret_cast<const HAL_AddressableLEDData*>(buffer);
 
-        std::vector<wpi::util::json> jsonData;
+        auto jsonData = wpi::util::json::array();
 
         for (size_t i = 0; i < numLeds; ++i) {
-          jsonData.push_back(
-              {{"r", data[i].r}, {"g", data[i].g}, {"b", data[i].b}});
+          jsonData.emplace_back(
+              wpi::util::json::object("r", static_cast<int64_t>(data[i].r), "g",
+                                      static_cast<int64_t>(data[i].g), "b",
+                                      static_cast<int64_t>(data[i].b)));
         }
 
         wpi::util::json payload;
-        payload["<data"] = jsonData;
+        payload["<data"] = std::move(jsonData);
 
         provider->ProcessHalCallback(payload);
       },
diff --git a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Analog.cpp b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Analog.cpp
index 423fe8a570..657d7d6f14 100644
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Analog.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Analog.cpp
@@ -12,7 +12,8 @@
       m_channel,                                                           \
       [](const char* name, void* param, const struct HAL_Value* value) {   \
         static_cast<HALSimWSProviderAnalogIn*>(param)->ProcessHalCallback( \
-            {{jsonid, static_cast<ctype>(value->data.v_##haltype)}});      \
+            wpi::util::json::object(                                       \
+                jsonid, static_cast<ctype>(value->data.v_##haltype)));     \
       },                                                                   \
       this, true)
 
@@ -54,9 +55,8 @@ void HALSimWSProviderAnalogIn::DoCancelCallbacks() {
 }
 
 void HALSimWSProviderAnalogIn::OnNetValueChanged(const wpi::util::json& json) {
-  wpi::util::json::const_iterator it;
-  if ((it = json.find(">voltage")) != json.end()) {
-    HALSIM_SetAnalogInVoltage(m_channel, it.value());
+  if (auto val = json.lookup(">voltage"); val && val->is_number()) {
+    HALSIM_SetAnalogInVoltage(m_channel, val->get_number());
   }
 }
 
diff --git a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_DIO.cpp b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_DIO.cpp
index 68a86632b5..6157a039cb 100644
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_DIO.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_DIO.cpp
@@ -12,7 +12,8 @@
       m_channel,                                                         \
       [](const char* name, void* param, const struct HAL_Value* value) { \
         static_cast<HALSimWSProviderDIO*>(param)->ProcessHalCallback(    \
-            {{jsonid, static_cast<ctype>(value->data.v_##haltype)}});    \
+            wpi::util::json::object(                                     \
+                jsonid, static_cast<ctype>(value->data.v_##haltype)));   \
       },                                                                 \
       this, true)
 
@@ -51,9 +52,8 @@ void HALSimWSProviderDIO::DoCancelCallbacks() {
 }
 
 void HALSimWSProviderDIO::OnNetValueChanged(const wpi::util::json& json) {
-  wpi::util::json::const_iterator it;
-  if ((it = json.find("<>value")) != json.end()) {
-    HALSIM_SetDIOValue(m_channel, static_cast<bool>(it.value()));
+  if (auto val = json.lookup("<>value"); val && val->is_bool()) {
+    HALSIM_SetDIOValue(m_channel, val->get_bool());
   }
 }
 
diff --git a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_DriverStation.cpp b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_DriverStation.cpp
index ff10f68ac1..b0b8fe3031 100644
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_DriverStation.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_DriverStation.cpp
@@ -12,13 +12,13 @@
 #include "wpi/hal/simulation/DriverStationData.h"
 #include "wpi/util/string.hpp"
 
-#define REGISTER(halsim, jsonid, ctype, haltype)                          \
-  HALSIM_RegisterDriverStation##halsim##Callback(                         \
-      [](const char* name, void* param, const struct HAL_Value* value) {  \
-        static_cast<HALSimWSProviderDriverStation*>(param)                \
-            ->ProcessHalCallback(                                         \
-                {{jsonid, static_cast<ctype>(value->data.v_##haltype)}}); \
-      },                                                                  \
+#define REGISTER(halsim, jsonid, ctype, haltype)                         \
+  HALSIM_RegisterDriverStation##halsim##Callback(                        \
+      [](const char* name, void* param, const struct HAL_Value* value) { \
+        static_cast<HALSimWSProviderDriverStation*>(param)               \
+            ->ProcessHalCallback(wpi::util::json::object(                \
+                jsonid, static_cast<ctype>(value->data.v_##haltype)));   \
+      },                                                                 \
       this, true)
 
 namespace wpilibws {
@@ -55,7 +55,7 @@ void HALSimWSProviderDriverStation::RegisterCallbacks() {
   m_newDataCbKey = HALSIM_RegisterDriverStationNewDataCallback(
       [](const char* name, void* param, const struct HAL_Value* value) {
         static_cast<HALSimWSProviderDriverStation*>(param)->ProcessHalCallback(
-            {{">new_data", true}});
+            wpi::util::json::object(">new_data", true));
       },
       this, true);
 
@@ -86,7 +86,7 @@ void HALSimWSProviderDriverStation::RegisterCallbacks() {
             break;
         }
         static_cast<HALSimWSProviderDriverStation*>(param)->ProcessHalCallback(
-            {{">station", station}});
+            wpi::util::json::object(">station", station));
       },
       this, true);
 
@@ -124,25 +124,25 @@ void HALSimWSProviderDriverStation::OnNetValueChanged(
     return;
   }
 
-  wpi::util::json::const_iterator it;
-  if ((it = json.find(">enabled")) != json.end()) {
-    HALSIM_SetDriverStationEnabled(it.value());
+  if (auto val = json.lookup(">enabled"); val && val->is_bool()) {
+    HALSIM_SetDriverStationEnabled(val->get_bool());
   }
-  if ((it = json.find(">robotMode")) != json.end()) {
-    HALSIM_SetDriverStationRobotMode(it.value());
+  if (auto val = json.lookup(">robotMode"); val && val->is_int()) {
+    HALSIM_SetDriverStationRobotMode(
+        static_cast<HAL_RobotMode>(val->get_int()));
   }
-  if ((it = json.find(">estop")) != json.end()) {
-    HALSIM_SetDriverStationEStop(it.value());
+  if (auto val = json.lookup(">estop"); val && val->is_bool()) {
+    HALSIM_SetDriverStationEStop(val->get_bool());
   }
-  if ((it = json.find(">fms")) != json.end()) {
-    HALSIM_SetDriverStationFmsAttached(it.value());
+  if (auto val = json.lookup(">fms"); val && val->is_bool()) {
+    HALSIM_SetDriverStationFmsAttached(val->get_bool());
   }
-  if ((it = json.find(">ds")) != json.end()) {
-    HALSIM_SetDriverStationDsAttached(it.value());
+  if (auto val = json.lookup(">ds"); val && val->is_bool()) {
+    HALSIM_SetDriverStationDsAttached(val->get_bool());
   }
 
-  if ((it = json.find(">station")) != json.end()) {
-    auto& station = it.value().get_ref<const std::string&>();
+  if (auto val = json.lookup(">station"); val && val->is_string()) {
+    auto& station = val->get_string();
     if (station == "red1") {
       HALSIM_SetDriverStationAllianceStationId(HAL_ALLIANCE_STATION_RED_1);
     } else if (station == "red2") {
@@ -158,17 +158,17 @@ void HALSimWSProviderDriverStation::OnNetValueChanged(
     }
   }
 
-  if ((it = json.find(">match_time")) != json.end()) {
-    HALSIM_SetDriverStationMatchTime(it.value());
+  if (auto val = json.lookup(">match_time"); val && val->is_number()) {
+    HALSIM_SetDriverStationMatchTime(val->get_number());
   }
-  if ((it = json.find(">game_data")) != json.end()) {
-    std::string message = it.value().get_ref<const std::string&>();
+  if (auto val = json.lookup(">game_data"); val && val->is_string()) {
+    std::string message = val->get_string();
     auto str = wpi::util::make_string(message);
     HALSIM_SetGameDataString(&str);
   }
 
   // Only notify usercode if we get the new data message
-  if ((it = json.find(">new_data")) != json.end()) {
+  if (json.contains(">new_data")) {
     HALSIM_NotifyDriverStationNewData();
   }
 }
diff --git a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Encoder.cpp b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Encoder.cpp
index 0d1dd33ada..8d13e2fb9c 100644
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Encoder.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Encoder.cpp
@@ -12,7 +12,8 @@
       m_channel,                                                          \
       [](const char* name, void* param, const struct HAL_Value* value) {  \
         static_cast<HALSimWSProviderEncoder*>(param)->ProcessHalCallback( \
-            {{jsonid, static_cast<ctype>(value->data.v_##haltype)}});     \
+            wpi::util::json::object(                                      \
+                jsonid, static_cast<ctype>(value->data.v_##haltype)));    \
       },                                                                  \
       this, true)
 
@@ -36,7 +37,7 @@ void HALSimWSProviderEncoder::RegisterCallbacks() {
         auto provider = static_cast<HALSimWSProviderEncoder*>(param);
         bool init = static_cast<bool>(value->data.v_boolean);
 
-        wpi::util::json payload = {{"<init", init}};
+        auto payload = wpi::util::json::object("<init", init);
 
         if (init) {
           payload["<channel_a"] =
@@ -52,9 +53,9 @@ void HALSimWSProviderEncoder::RegisterCallbacks() {
       m_channel,
       [](const char* name, void* param, const struct HAL_Value* value) {
         auto provider = static_cast<HALSimWSProviderEncoder*>(param);
-        provider->ProcessHalCallback(
-            {{">count", static_cast<int32_t>(value->data.v_int +
-                                             provider->m_countOffset)}});
+        provider->ProcessHalCallback(wpi::util::json::object(
+            ">count",
+            static_cast<int32_t>(value->data.v_int + provider->m_countOffset)));
       },
       this, true);
   m_periodCbKey = REGISTER(Period, ">period", double, double);
@@ -96,13 +97,12 @@ void HALSimWSProviderEncoder::DoCancelCallbacks() {
 }
 
 void HALSimWSProviderEncoder::OnNetValueChanged(const wpi::util::json& json) {
-  wpi::util::json::const_iterator it;
-  if ((it = json.find(">count")) != json.end()) {
-    HALSIM_SetEncoderCount(m_channel,
-                           static_cast<int32_t>(it.value()) - m_countOffset);
+  if (auto val = json.lookup(">count"); val && val->is_int()) {
+    HALSIM_SetEncoderCount(m_channel, val->get_int() - m_countOffset);
   }
-  if ((it = json.find(">period")) != json.end()) {
-    HALSIM_SetEncoderPeriod(m_channel, it.value());
+
+  if (auto val = json.lookup(">period"); val && val->is_number()) {
+    HALSIM_SetEncoderPeriod(m_channel, val->get_number());
   }
 }
 
diff --git a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_HAL.cpp b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_HAL.cpp
index 778b20fe3c..2f0214153f 100644
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_HAL.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_HAL.cpp
@@ -27,14 +27,14 @@ void HALSimWSProviderHAL::RegisterCallbacks() {
   m_simPeriodicBeforeCbKey = HALSIM_RegisterSimPeriodicBeforeCallback(
       [](void* param) {
         static_cast<HALSimWSProviderHAL*>(param)->ProcessHalCallback(
-            {{">sim_periodic_before", true}});
+            wpi::util::json::object(">sim_periodic_before", true));
       },
       this);
 
   m_simPeriodicAfterCbKey = HALSIM_RegisterSimPeriodicAfterCallback(
       [](void* param) {
         static_cast<HALSimWSProviderHAL*>(param)->ProcessHalCallback(
-            {{">sim_periodic_after", true}});
+            wpi::util::json::object(">sim_periodic_after", true));
       },
       this);
 }
diff --git a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Joystick.cpp b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Joystick.cpp
index 9411f2df6a..040eab3d39 100644
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Joystick.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Joystick.cpp
@@ -8,6 +8,7 @@
 #include <atomic>
 #include <vector>
 
+#include "wpi/hal/DriverStationTypes.h"
 #include "wpi/hal/Ports.h"
 #include "wpi/hal/simulation/DriverStationData.h"
 
@@ -103,31 +104,34 @@ void HALSimWSProviderJoystick::OnNetValueChanged(const wpi::util::json& json) {
     return;
   }
 
-  wpi::util::json::const_iterator it;
-  if ((it = json.find(">axes")) != json.end()) {
+  if (auto val = json.lookup(">axes"); val && val->is_array()) {
+    auto& arr = val->get_array();
     HAL_JoystickAxes axes{};
-    wpi::util::json::size_type axesCount = std::min(
-        it.value().size(),
-        static_cast<wpi::util::json::size_type>(HAL_MAX_JOYSTICK_AXES));
+    size_t axesCount =
+        std::min(arr.size(), static_cast<size_t>(HAL_MAX_JOYSTICK_AXES));
     axes.available = (1 << axesCount) - 1;
-    for (wpi::util::json::size_type i = 0; i < axesCount; i++) {
-      axes.axes[i] = it.value()[i];
+    for (size_t i = 0; i < axesCount; i++) {
+      if (arr[i].is_number()) {
+        axes.axes[i] = arr[i].get_number();
+      } else {
+        axes.axes[i] = 0.0;
+      }
     }
 
     HALSIM_SetJoystickAxes(m_channel, &axes);
   }
 
-  if ((it = json.find(">buttons")) != json.end()) {
+  if (auto val = json.lookup(">buttons"); val && val->is_array()) {
     HAL_JoystickButtons buttons{};
-    wpi::util::json::size_type buttonsCount = std::min(
-        it.value().size(), static_cast<wpi::util::json::size_type>(64));
+    auto& arr = val->get_array();
+    size_t buttonsCount = std::min(arr.size(), static_cast<size_t>(64));
     if (buttonsCount < 64) {
       buttons.available = (1ULL << buttonsCount) - 1;
     } else {
       buttons.available = (std::numeric_limits<uint64_t>::max)();
     }
-    for (wpi::util::json::size_type i = 0; i < buttonsCount; i++) {
-      if (it.value()[i]) {
+    for (size_t i = 0; i < buttonsCount; i++) {
+      if (arr[i].is_bool() && arr[i].get_bool()) {
         buttons.buttons |= 1llu << i;
       }
     }
@@ -135,14 +139,18 @@ void HALSimWSProviderJoystick::OnNetValueChanged(const wpi::util::json& json) {
     HALSIM_SetJoystickButtons(m_channel, &buttons);
   }
 
-  if ((it = json.find(">povs")) != json.end()) {
+  if (auto val = json.lookup(">povs"); val && val->is_array()) {
     HAL_JoystickPOVs povs{};
-    wpi::util::json::size_type povsCount = std::min(
-        it.value().size(),
-        static_cast<wpi::util::json::size_type>(HAL_MAX_JOYSTICK_POVS));
+    auto& arr = val->get_array();
+    size_t povsCount =
+        std::min(arr.size(), static_cast<size_t>(HAL_MAX_JOYSTICK_POVS));
     povs.available = (1 << povsCount) - 1;
-    for (wpi::util::json::size_type i = 0; i < povsCount; i++) {
-      povs.povs[i] = it.value()[i];
+    for (size_t i = 0; i < povsCount; i++) {
+      if (arr[i].is_int()) {
+        povs.povs[i] = static_cast<HAL_JoystickPOV>(arr[i].get_int());
+      } else {
+        povs.povs[i] = HAL_JOYSTICK_POV_CENTERED;
+      }
     }
 
     HALSIM_SetJoystickPOVs(m_channel, &povs);
diff --git a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_PCM.cpp b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_PCM.cpp
index d158b4f803..347d60af78 100644
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_PCM.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_PCM.cpp
@@ -12,7 +12,8 @@
       m_channel,                                                         \
       [](const char* name, void* param, const struct HAL_Value* value) { \
         static_cast<HALSimWSProviderPCM*>(param)->ProcessHalCallback(    \
-            {{jsonid, static_cast<ctype>(value->data.v_##haltype)}});    \
+            wpi::util::json::object(                                     \
+                jsonid, static_cast<ctype>(value->data.v_##haltype)));   \
       },                                                                 \
       this, true)
 namespace wpilibws {
diff --git a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_PWM.cpp b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_PWM.cpp
index d49f19a78f..4d27a7a650 100644
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_PWM.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_PWM.cpp
@@ -12,7 +12,8 @@
       m_channel,                                                         \
       [](const char* name, void* param, const struct HAL_Value* value) { \
         static_cast<HALSimWSProviderPWM*>(param)->ProcessHalCallback(    \
-            {{jsonid, static_cast<ctype>(value->data.v_##haltype)}});    \
+            wpi::util::json::object(                                     \
+                jsonid, static_cast<ctype>(value->data.v_##haltype)));   \
       },                                                                 \
       this, true)
 namespace wpilibws {
diff --git a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_RoboRIO.cpp b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_RoboRIO.cpp
index 3f660b2dfd..55437b02c6 100644
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_RoboRIO.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_RoboRIO.cpp
@@ -11,7 +11,8 @@
   HALSIM_RegisterRoboRio##halsim##Callback(                               \
       [](const char* name, void* param, const struct HAL_Value* value) {  \
         static_cast<HALSimWSProviderRoboRIO*>(param)->ProcessHalCallback( \
-            {{jsonid, static_cast<ctype>(value->data.v_##haltype)}});     \
+            wpi::util::json::object(                                      \
+                jsonid, static_cast<ctype>(value->data.v_##haltype)));    \
       },                                                                  \
       this, true)
 
@@ -54,22 +55,20 @@ void HALSimWSProviderRoboRIO::DoCancelCallbacks() {
 }
 
 void HALSimWSProviderRoboRIO::OnNetValueChanged(const wpi::util::json& json) {
-  wpi::util::json::const_iterator it;
-  if ((it = json.find(">vin_voltage")) != json.end()) {
-    HALSIM_SetRoboRioVInVoltage(it.value());
+  if (auto val = json.lookup(">vin_voltage"); val && val->is_number()) {
+    HALSIM_SetRoboRioVInVoltage(val->get_number());
   }
-
-  if ((it = json.find(">3v3_voltage")) != json.end()) {
-    HALSIM_SetRoboRioUserVoltage3V3(it.value());
+  if (auto val = json.lookup(">3v3_voltage"); val && val->is_number()) {
+    HALSIM_SetRoboRioUserVoltage3V3(val->get_number());
   }
-  if ((it = json.find(">3v3_current")) != json.end()) {
-    HALSIM_SetRoboRioUserCurrent3V3(it.value());
+  if (auto val = json.lookup(">3v3_current"); val && val->is_number()) {
+    HALSIM_SetRoboRioUserCurrent3V3(val->get_number());
   }
-  if ((it = json.find(">3v3_active")) != json.end()) {
-    HALSIM_SetRoboRioUserActive3V3(static_cast<bool>(it.value()));
+  if (auto val = json.lookup(">3v3_active"); val && val->is_bool()) {
+    HALSIM_SetRoboRioUserActive3V3(val->get_bool());
   }
-  if ((it = json.find(">3v3_faults")) != json.end()) {
-    HALSIM_SetRoboRioUserFaults3V3(it.value());
+  if (auto val = json.lookup(">3v3_faults"); val && val->is_number()) {
+    HALSIM_SetRoboRioUserFaults3V3(val->get_number());
   }
 }
 
diff --git a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_SimDevice.cpp b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_SimDevice.cpp
index b2e4b21819..7d21e98b31 100644
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_SimDevice.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_SimDevice.cpp
@@ -62,53 +62,59 @@ void HALSimWSProviderSimDevice::CancelCallbacks() {
 }
 
 void HALSimWSProviderSimDevice::OnNetValueChanged(const wpi::util::json& json) {
-  auto it = json.cbegin();
-  auto end = json.cend();
-
   std::shared_lock lock(m_vhLock);
-  for (; it != end; ++it) {
-    auto vd = m_valueHandles.find(it.key());
+  for (auto&& [key, jvalue] : json.get_object()) {
+    auto vd = m_valueHandles.find(key);
     if (vd != m_valueHandles.end()) {
       HAL_Value value;
       value.type = vd->second.valueType;
       switch (value.type) {
         case HAL_BOOLEAN:
-          value.data.v_boolean = static_cast<bool>(it.value()) ? 1 : 0;
+          if (jvalue.is_bool()) {
+            value.data.v_boolean = jvalue.get_bool() ? 1 : 0;
+          }
           break;
         case HAL_DOUBLE:
-          value.data.v_double = it.value();
-          value.data.v_double -= vd->second.doubleOffset;
+          if (jvalue.is_number()) {
+            value.data.v_double = jvalue.get_double();
+            value.data.v_double -= vd->second.doubleOffset;
+          }
           break;
         case HAL_ENUM: {
-          if (it->is_string()) {
+          if (jvalue.is_string()) {
             auto& options = vd->second.options;
-            auto& str = it.value().get_ref<const std::string&>();
+            auto& str = jvalue.get_string();
             auto optionIt =
                 std::find_if(options.begin(), options.end(),
                              [&](const std::string& v) { return v == str; });
             if (optionIt != options.end()) {
               value.data.v_enum = optionIt - options.begin();
             }
-          } else if (it->is_number()) {
+          } else if (jvalue.is_float() || jvalue.is_double()) {
             auto& values = vd->second.optionValues;
-            double num = it.value();
+            double num = jvalue.get_number();
             auto valueIt = std::find_if(
                 values.begin(), values.end(),
                 [&](double v) { return std::fabs(v - num) < 1e-4; });
             if (valueIt != values.end()) {
               value.data.v_enum = valueIt - values.begin();
             }
+          } else if (jvalue.is_int()) {
+            value.data.v_enum = jvalue.get_int();
           }
-          value.data.v_enum = it.value();
           break;
         }
         case HAL_INT:
-          value.data.v_int = it.value();
-          value.data.v_int -= vd->second.intOffset;
+          if (jvalue.is_int()) {
+            value.data.v_int = jvalue.get_int();
+            value.data.v_int -= vd->second.intOffset;
+          }
           break;
         case HAL_LONG:
-          value.data.v_long = it.value();
-          value.data.v_long -= vd->second.intOffset;
+          if (jvalue.is_int()) {
+            value.data.v_long = jvalue.get_int();
+            value.data.v_long -= vd->second.intOffset;
+          }
           break;
         default:
           break;
@@ -193,29 +199,31 @@ void HALSimWSProviderSimDevice::OnValueChanged(SimDeviceValueData* valueData,
   if (ws) {
     switch (value->type) {
       case HAL_BOOLEAN:
-        ProcessHalCallback(
-            {{valueData->key, static_cast<bool>(value->data.v_boolean)}});
+        ProcessHalCallback(wpi::util::json::object(
+            valueData->key, static_cast<bool>(value->data.v_boolean)));
         break;
       case HAL_DOUBLE:
-        ProcessHalCallback(
-            {{valueData->key, value->data.v_double + valueData->doubleOffset}});
+        ProcessHalCallback(wpi::util::json::object(
+            valueData->key, value->data.v_double + valueData->doubleOffset));
         break;
       case HAL_ENUM: {
         int v = value->data.v_enum;
         if (v >= 0 && v < static_cast<int>(valueData->optionValues.size())) {
-          ProcessHalCallback({{valueData->key, valueData->optionValues[v]}});
+          ProcessHalCallback(wpi::util::json::object(
+              valueData->key, valueData->optionValues[v]));
         } else if (v >= 0 && v < static_cast<int>(valueData->options.size())) {
-          ProcessHalCallback({{valueData->key, valueData->options[v]}});
+          ProcessHalCallback(
+              wpi::util::json::object(valueData->key, valueData->options[v]));
         }
         break;
       }
       case HAL_INT:
-        ProcessHalCallback(
-            {{valueData->key, value->data.v_int + valueData->intOffset}});
+        ProcessHalCallback(wpi::util::json::object(
+            valueData->key, value->data.v_int + valueData->intOffset));
         break;
       case HAL_LONG:
-        ProcessHalCallback(
-            {{valueData->key, value->data.v_long + valueData->intOffset}});
+        ProcessHalCallback(wpi::util::json::object(
+            valueData->key, value->data.v_long + valueData->intOffset));
         break;
       default:
         break;
@@ -254,8 +262,10 @@ void HALSimWSProviderSimDevice::ProcessHalCallback(
     const wpi::util::json& payload) {
   auto ws = m_ws.lock();
   if (ws) {
-    wpi::util::json netValue = {
-        {"type", m_type}, {"device", m_deviceId}, {"data", payload}};
+    auto netValue = wpi::util::json::object();
+    netValue["type"] = m_type;
+    netValue["device"] = m_deviceId;
+    netValue["data"] = payload;
     ws->OnSimValueChanged(netValue);
   }
 }
diff --git a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Solenoid.cpp b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Solenoid.cpp
index d00f4ce538..7d70e8a525 100644
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Solenoid.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_Solenoid.cpp
@@ -18,7 +18,8 @@
       m_pcmIndex, m_solenoidIndex,                                         \
       [](const char* name, void* param, const struct HAL_Value* value) {   \
         static_cast<HALSimWSProviderSolenoid*>(param)->ProcessHalCallback( \
-            {{jsonid, static_cast<ctype>(value->data.v_##haltype)}});      \
+            wpi::util::json::object(                                       \
+                jsonid, static_cast<ctype>(value->data.v_##haltype)));     \
       },                                                                   \
       this, true)
 
diff --git a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_dPWM.cpp b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_dPWM.cpp
index 47fbcf63be..435c12d56f 100644
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_dPWM.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_dPWM.cpp
@@ -12,7 +12,8 @@
       m_channel,                                                             \
       [](const char* name, void* param, const struct HAL_Value* value) {     \
         static_cast<HALSimWSProviderDigitalPWM*>(param)->ProcessHalCallback( \
-            {{jsonid, static_cast<ctype>(value->data.v_##haltype)}});        \
+            wpi::util::json::object(                                         \
+                jsonid, static_cast<ctype>(value->data.v_##haltype)));       \
       },                                                                     \
       this, true)
 
diff --git a/simulation/halsim_ws_core/src/main/native/include/wpi/halsim/ws_core/HALSimBaseWebSocketConnection.hpp b/simulation/halsim_ws_core/src/main/native/include/wpi/halsim/ws_core/HALSimBaseWebSocketConnection.hpp
index 90930ec443..701ecfca27 100644
--- a/simulation/halsim_ws_core/src/main/native/include/wpi/halsim/ws_core/HALSimBaseWebSocketConnection.hpp
+++ b/simulation/halsim_ws_core/src/main/native/include/wpi/halsim/ws_core/HALSimBaseWebSocketConnection.hpp
@@ -6,7 +6,9 @@
 
 #include <memory>
 
-#include "wpi/util/json_fwd.hpp"
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpilibws {
 
diff --git a/simulation/halsim_ws_core/src/main/native/include/wpi/halsim/ws_core/WSHalProviders.hpp b/simulation/halsim_ws_core/src/main/native/include/wpi/halsim/ws_core/WSHalProviders.hpp
index 5c7d5f62b0..41ae362559 100644
--- a/simulation/halsim_ws_core/src/main/native/include/wpi/halsim/ws_core/WSHalProviders.hpp
+++ b/simulation/halsim_ws_core/src/main/native/include/wpi/halsim/ws_core/WSHalProviders.hpp
@@ -13,8 +13,10 @@
 
 #include "wpi/hal/simulation/NotifyListener.h"
 #include "wpi/halsim/ws_core/WSBaseProvider.hpp"
-#include "wpi/util/json_fwd.hpp"
-#include "wpi/util/mutex.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpilibws {
 
diff --git a/simulation/halsim_ws_server/src/main/native/cpp/HALSimHttpConnection.cpp b/simulation/halsim_ws_server/src/main/native/cpp/HALSimHttpConnection.cpp
index a77e7119f5..2a942ae6e9 100644
--- a/simulation/halsim_ws_server/src/main/native/cpp/HALSimHttpConnection.cpp
+++ b/simulation/halsim_ws_server/src/main/native/cpp/HALSimHttpConnection.cpp
@@ -54,16 +54,12 @@ void HALSimHttpConnection::ProcessWsUpgrade() {
       return;
     }
 
-    wpi::util::json j;
-    try {
-      j = wpi::util::json::parse(msg);
-    } catch (const wpi::util::json::parse_error& e) {
-      std::string err("JSON parse failed: ");
-      err += e.what();
-      m_websocket->Fail(400, err);
+    auto j = wpi::util::json::parse(msg);
+    if (!j) {
+      m_websocket->Fail(400, fmt::format("JSON parse failed: {}", j.error()));
       return;
     }
-    m_server->OnNetValueChanged(j);
+    m_server->OnNetValueChanged(*j);
   });
 
   m_websocket->closed.connect([this](uint16_t, auto) {
@@ -80,11 +76,11 @@ void HALSimHttpConnection::ProcessWsUpgrade() {
 void HALSimHttpConnection::OnSimValueChanged(const wpi::util::json& msg) {
   // Skip sending if this message is not in the allowed filter list
   try {
-    auto& type = msg.at("type").get_ref<const std::string&>();
+    auto& type = msg.at("type").get_string();
     if (!m_server->CanSendMessage(type)) {
       return;
     }
-  } catch (wpi::util::json::exception& e) {
+  } catch (std::logic_error& e) {
     wpi::util::print(stderr, "Error with message: {}\n", e.what());
   }
 
diff --git a/simulation/halsim_ws_server/src/main/native/cpp/HALSimWeb.cpp b/simulation/halsim_ws_server/src/main/native/cpp/HALSimWeb.cpp
index 035c70ed14..0e7af186be 100644
--- a/simulation/halsim_ws_server/src/main/native/cpp/HALSimWeb.cpp
+++ b/simulation/halsim_ws_server/src/main/native/cpp/HALSimWeb.cpp
@@ -162,8 +162,8 @@ void HALSimWeb::OnNetValueChanged(const wpi::util::json& msg) {
   // generate the key
 
   try {
-    auto& type = msg.at("type").get_ref<const std::string&>();
-    auto& device = msg.at("device").get_ref<const std::string&>();
+    auto& type = msg.at("type").get_string();
+    auto& device = msg.at("device").get_string();
 
     wpi::util::SmallString<64> key;
     key.append(type);
@@ -176,7 +176,7 @@ void HALSimWeb::OnNetValueChanged(const wpi::util::json& msg) {
     if (provider) {
       provider->OnNetValueChanged(msg.at("data"));
     }
-  } catch (wpi::util::json::exception& e) {
+  } catch (std::logic_error& e) {
     wpi::util::print(stderr, "Error with incoming message: {}\n", e.what());
   }
 }
diff --git a/simulation/halsim_ws_server/src/main/native/include/wpi/halsim/ws_server/HALSimHttpConnection.hpp b/simulation/halsim_ws_server/src/main/native/include/wpi/halsim/ws_server/HALSimHttpConnection.hpp
index 507909e47f..7bd72cc9d1 100644
--- a/simulation/halsim_ws_server/src/main/native/include/wpi/halsim/ws_server/HALSimHttpConnection.hpp
+++ b/simulation/halsim_ws_server/src/main/native/include/wpi/halsim/ws_server/HALSimHttpConnection.hpp
@@ -4,7 +4,6 @@
 
 #pragma once
 
-#include <cinttypes>
 #include <memory>
 #include <string_view>
 #include <utility>
@@ -12,10 +11,11 @@
 #include "wpi/halsim/ws_core/HALSimBaseWebSocketConnection.hpp"
 #include "wpi/halsim/ws_server/HALSimWeb.hpp"
 #include "wpi/net/HttpWebSocketServerConnection.hpp"
-#include "wpi/net/uv/AsyncFunction.hpp"
 #include "wpi/net/uv/Buffer.hpp"
-#include "wpi/util/json_fwd.hpp"
-#include "wpi/util/mutex.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpilibws {
 
diff --git a/simulation/halsim_ws_server/src/main/native/include/wpi/halsim/ws_server/HALSimWeb.hpp b/simulation/halsim_ws_server/src/main/native/include/wpi/halsim/ws_server/HALSimWeb.hpp
index 0fa352424c..cd5b9ed160 100644
--- a/simulation/halsim_ws_server/src/main/native/include/wpi/halsim/ws_server/HALSimWeb.hpp
+++ b/simulation/halsim_ws_server/src/main/native/include/wpi/halsim/ws_server/HALSimWeb.hpp
@@ -16,7 +16,10 @@
 #include "wpi/net/uv/Loop.hpp"
 #include "wpi/net/uv/Tcp.hpp"
 #include "wpi/util/StringMap.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpilibws {
 
diff --git a/simulation/halsim_ws_server/src/test/native/cpp/WebServerClientTest.cpp b/simulation/halsim_ws_server/src/test/native/cpp/WebServerClientTest.cpp
index 06bd4e43b3..bbf8e68ac7 100644
--- a/simulation/halsim_ws_server/src/test/native/cpp/WebServerClientTest.cpp
+++ b/simulation/halsim_ws_server/src/test/native/cpp/WebServerClientTest.cpp
@@ -44,18 +44,15 @@ void WebServerClientTest::InitializeWebSocket(const std::string& host, int port,
   });
 
   m_websocket->text.connect([this](auto msg, bool) {
-    wpi::util::json j;
-    try {
-      j = wpi::util::json::parse(msg);
-    } catch (const wpi::util::json::parse_error& e) {
-      std::string err("JSON parse failed: ");
-      err += e.what();
+    auto j = wpi::util::json::parse(msg);
+    if (!j) {
+      auto err = fmt::format("JSON parse failed: {}", j.error());
       wpi::util::print(stderr, "{}\n", err);
       m_websocket->Fail(1003, err);
       return;
     }
     // Save last message received
-    m_json = j;
+    m_json = *j;
   });
 
   m_websocket->closed.connect([this](uint16_t, auto) {
diff --git a/simulation/halsim_ws_server/src/test/native/cpp/main.cpp b/simulation/halsim_ws_server/src/test/native/cpp/main.cpp
index 9b35d23cc8..8c3544c857 100644
--- a/simulation/halsim_ws_server/src/test/native/cpp/main.cpp
+++ b/simulation/halsim_ws_server/src/test/native/cpp/main.cpp
@@ -7,6 +7,7 @@
 #include <memory>
 #include <string>
 #include <thread>
+#include <utility>
 
 #include <gtest/gtest.h>
 
@@ -78,14 +79,13 @@ TEST_F(WebServerIntegrationTest, DISABLED_DigitalOutput) {
   bool test_value = true;  // Default value from HAL initialization
   try {
     auto& msg = m_webserverClient->GetLastMessage();
-    test_type = msg.at("type").get_ref<const std::string&>();
-    test_device = msg.at("device").get_ref<const std::string&>();
+    test_type = msg.at("type").get_string();
+    test_device = msg.at("device").get_string();
     auto& data = msg.at("data");
-    wpi::util::json::const_iterator it = data.find("<>value");
-    if (it != data.end()) {
-      test_value = it.value();
+    if (auto val = data.lookup("<>value"); val && val->is_bool()) {
+      test_value = val->get_bool();
     }
-  } catch (wpi::util::json::exception& e) {
+  } catch (std::logic_error& e) {
     wpi::util::print(stderr, "Error with incoming message: {}\n", e.what());
   }
 
@@ -109,10 +109,11 @@ TEST_F(WebServerIntegrationTest, DISABLED_DigitalInput) {
         return;
       }
       if (IsConnectedClientWS()) {
-        wpi::util::json msg = {{"type", "DIO"},
-                               {"device", std::to_string(PIN)},
-                               {"data", {{"<>value", EXPECTED_VALUE}}}};
-        wpi::util::print("***** Input JSON: {}\n", msg.dump());
+        wpi::util::json msg = wpi::util::json::object();
+        msg["type"] = "DIO";
+        msg["device"] = std::to_string(PIN);
+        msg["data"] = wpi::util::json::object("<>value", EXPECTED_VALUE);
+        wpi::util::print("***** Input JSON: {}\n", msg.to_string());
         m_webserverClient->SendMessage(msg);
         done = true;
       }
@@ -143,11 +144,14 @@ TEST_F(WebServerIntegrationTest, DriverStation) {
         return;
       }
       if (IsConnectedClientWS()) {
-        wpi::util::json msg = {
-            {"type", "DriverStation"},
-            {"device", ""},
-            {"data", {{">enabled", EXPECTED_VALUE}, {">new_data", true}}}};
-        wpi::util::print("***** Input JSON: {}\n", msg.dump());
+        auto data = wpi::util::json::object();
+        data[">enabled"] = EXPECTED_VALUE;
+        data[">new_data"] = true;
+        wpi::util::json msg = wpi::util::json::object();
+        msg["type"] = "DriverStation";
+        msg["device"] = "";
+        msg["data"] = std::move(data);
+        wpi::util::print("***** Input JSON: {}\n", msg.to_string());
         m_webserverClient->SendMessage(msg);
         done = true;
       }
diff --git a/simulation/halsim_xrp/src/main/native/cpp/HALSimXRP.cpp b/simulation/halsim_xrp/src/main/native/cpp/HALSimXRP.cpp
index c2a30408eb..88422caf93 100644
--- a/simulation/halsim_xrp/src/main/native/cpp/HALSimXRP.cpp
+++ b/simulation/halsim_xrp/src/main/native/cpp/HALSimXRP.cpp
@@ -107,8 +107,8 @@ void HALSimXRP::ParsePacket(std::span<const uint8_t> packet) {
 
 void HALSimXRP::OnNetValueChanged(const wpi::util::json& msg) {
   try {
-    auto& type = msg.at("type").get_ref<const std::string&>();
-    auto& device = msg.at("device").get_ref<const std::string&>();
+    auto& type = msg.at("type").get_string();
+    auto& device = msg.at("device").get_string();
 
     wpi::util::SmallString<64> key;
     key.append(type);
@@ -121,16 +121,17 @@ void HALSimXRP::OnNetValueChanged(const wpi::util::json& msg) {
     if (provider) {
       provider->OnNetValueChanged(msg.at("data"));
     }
-  } catch (wpi::util::json::exception& e) {
+  } catch (std::logic_error& e) {
     wpi::util::print(stderr, "Error with incoming message: {}\n", e.what());
   }
 }
 
 void HALSimXRP::OnSimValueChanged(const wpi::util::json& simData) {
   // We'll use a signal from robot code to send all the data
-  if (simData["type"] == "HAL") {
-    auto halData = simData["data"];
-    if (halData.find(">sim_periodic_after") != halData.end()) {
+  auto type = simData.lookup("type");
+  if (type->is_string() && type->get_string() == "HAL") {
+    auto halData = simData.lookup("data");
+    if (halData && halData->contains(">sim_periodic_after")) {
       SendStateToXRP();
     }
   } else {
diff --git a/simulation/halsim_xrp/src/main/native/cpp/XRP.cpp b/simulation/halsim_xrp/src/main/native/cpp/XRP.cpp
index 5993a32dc0..9dbe119426 100644
--- a/simulation/halsim_xrp/src/main/native/cpp/XRP.cpp
+++ b/simulation/halsim_xrp/src/main/native/cpp/XRP.cpp
@@ -6,6 +6,7 @@
 
 #include <bit>
 #include <string>
+#include <utility>
 
 #include <fmt/format.h>
 
@@ -33,21 +34,23 @@ XRP::XRP()
 }
 
 void XRP::HandleWPILibUpdate(const wpi::util::json& data) {
-  if (data.count("type") == 0) {
+  auto type = data.lookup("type");
+  if (!type || !type->is_string()) {
     return;
   }
 
-  if (data["type"] == "DriverStation") {
+  auto& typeStr = type->get_string();
+  if (typeStr == "DriverStation") {
     HandleDriverStationSimValueChanged(data);
-  } else if (data["type"] == "XRPMotor") {
+  } else if (typeStr == "XRPMotor") {
     HandleMotorSimValueChanged(data);
-  } else if (data["type"] == "XRPServo") {
+  } else if (typeStr == "XRPServo") {
     HandleServoSimValueChanged(data);
-  } else if (data["type"] == "DIO") {
+  } else if (typeStr == "DIO") {
     HandleDIOSimValueChanged(data);
-  } else if (data["type"] == "Gyro") {
+  } else if (typeStr == "Gyro") {
     HandleGyroSimValueChanged(data);
-  } else if (data["type"] == "Encoder") {
+  } else if (typeStr == "Encoder") {
     HandleEncoderSimValueChanged(data);
   }
 }
@@ -108,56 +111,84 @@ void XRP::SetupXRPSendBuffer(wpi::net::raw_uv_ostream& buf) {
 
 // WPILib Sim Handlers
 void XRP::HandleDriverStationSimValueChanged(const wpi::util::json& data) {
-  auto dsData = data["data"];
-  if (dsData.find(">enabled") != dsData.end()) {
-    m_robot_enabled = dsData[">enabled"];
+  auto dsData = data.lookup("data");
+  if (!dsData || !dsData->is_object()) {
+    return;
+  }
+  auto enabled = dsData->lookup(">enabled");
+  if (enabled && enabled->is_bool()) {
+    m_robot_enabled = enabled->get_bool();
   }
 }
 
 void XRP::HandleMotorSimValueChanged(const wpi::util::json& data) {
   int deviceId = -1;
-  auto motorData = data["data"];
+  auto motorData = data.lookup("data");
+  if (!motorData || !motorData->is_object()) {
+    return;
+  }
 
-  if (data["device"] == "motorL") {
+  auto device = data.lookup("device");
+  if (!device || !device->is_string()) {
+    return;
+  }
+
+  auto& deviceStr = device->get_string();
+  if (deviceStr == "motorL") {
     deviceId = 0;
-  } else if (data["device"] == "motorR") {
+  } else if (deviceStr == "motorR") {
     deviceId = 1;
-  } else if (data["device"] == "motor3") {
+  } else if (deviceStr == "motor3") {
     deviceId = 2;
-  } else if (data["device"] == "motor4") {
+  } else if (deviceStr == "motor4") {
     deviceId = 3;
   }
 
-  if (deviceId != -1 && motorData.find("<duty_cycle") != motorData.end()) {
-    m_motor_outputs[deviceId] = motorData["<duty_cycle"];
+  auto dutyCycle = motorData->lookup("<duty_cycle");
+  if (deviceId != -1 && dutyCycle && dutyCycle->is_number()) {
+    m_motor_outputs[deviceId] = dutyCycle->get_number();
   }
 }
 
 void XRP::HandleServoSimValueChanged(const wpi::util::json& data) {
   int deviceId = -1;
-  auto servoData = data["data"];
+  auto servoData = data.lookup("data");
+  if (!servoData || !servoData->is_object()) {
+    return;
+  }
 
-  if (data["device"] == "servo1") {
+  auto device = data.lookup("device");
+  if (!device || !device->is_string()) {
+    return;
+  }
+
+  auto& deviceStr = device->get_string();
+  if (deviceStr == "servo1") {
     deviceId = 4;
-  } else if (data["device"] == "servo2") {
+  } else if (deviceStr == "servo2") {
     deviceId = 5;
-  } else if (data["device"] == "servo3") {
+  } else if (deviceStr == "servo3") {
     deviceId = 6;
-  } else if (data["device"] == "servo4") {
+  } else if (deviceStr == "servo4") {
     deviceId = 7;
   }
 
-  if (deviceId != -1 && servoData.find("<position") != servoData.end()) {
-    m_servo_outputs[deviceId] = servoData["<position"];
+  auto position = servoData->lookup("<position");
+  if (deviceId != -1 && position && position->is_number()) {
+    m_servo_outputs[deviceId] = position->get_number();
   }
 }
 
 void XRP::HandleDIOSimValueChanged(const wpi::util::json& data) {
   int deviceId = -1;
-  auto dioData = data["data"];
+  auto dioData = data.lookup("data");
 
+  auto device = data.lookup("device");
+  if (!device || !device->is_string()) {
+    return;
+  }
   try {
-    deviceId = std::stoi(data["device"].get<std::string>());
+    deviceId = std::stoi(device->get_string());
   } catch (const std::invalid_argument&) {
     deviceId = -1;
   }
@@ -167,26 +198,31 @@ void XRP::HandleDIOSimValueChanged(const wpi::util::json& data) {
     return;
   }
 
-  if (dioData.find("<init") != dioData.end() && dioData["<init"]) {
+  auto init = dioData->lookup("<init");
+  if (init && init->is_bool() && init->get_bool()) {
     // All DIOs are initialized as inputs by default
     m_digital_inputs.emplace(deviceId, false);
   }
 
-  if (dioData.find("<input") != dioData.end() && dioData["<input"] == false) {
+  auto input = dioData->lookup("<input");
+  if (input && input->is_bool() && !input->get_bool()) {
     // We're registering an output device
     // Remove from the digital inputs list (if present)
     m_digital_inputs.erase(deviceId);
     m_digital_outputs.emplace(deviceId, false);
   }
 
-  if (dioData.find("<>value") != dioData.end() &&
-      m_digital_outputs.count(deviceId) > 0) {
-    m_digital_outputs[deviceId] = dioData["<>value"];
+  auto value = dioData->lookup("<>value");
+  if (value && value->is_bool() && m_digital_outputs.count(deviceId) > 0) {
+    m_digital_outputs[deviceId] = value->get_bool();
   }
 }
 
 void XRP::HandleGyroSimValueChanged(const wpi::util::json& data) {
-  m_gyro_name = data["device"].get<std::string>();
+  auto name = data.lookup("device");
+  if (name && name->is_string()) {
+    m_gyro_name = name->get_string();
+  }
 }
 
 void XRP::HandleEncoderSimValueChanged(const wpi::util::json& data) {
@@ -196,10 +232,18 @@ void XRP::HandleEncoderSimValueChanged(const wpi::util::json& data) {
   // 8/9 -> Encoder 2
   // 10/11 -> Encoder 3
   int deviceId = -1;
-  auto encData = data["data"];
+  auto encData = data.lookup("data");
+  if (!encData || !encData->is_object()) {
+    return;
+  }
+
+  auto device = data.lookup("device");
+  if (!device || !device->is_string()) {
+    return;
+  }
 
   try {
-    deviceId = std::stoi(data["device"].get<std::string>());
+    deviceId = std::stoi(device->get_string());
   } catch (const std::invalid_argument&) {
     deviceId = -1;
   }
@@ -208,10 +252,14 @@ void XRP::HandleEncoderSimValueChanged(const wpi::util::json& data) {
     return;
   }
 
-  if (encData.find("<init") != encData.end() && encData["<init"]) {
+  auto init = encData->lookup("<init");
+  auto jchA = encData->lookup("<channel_a");
+  auto jchB = encData->lookup("<channel_b");
+  if (init && init->is_bool() && init->get_bool() && jchA && jchA->is_int() &&
+      jchB && jchB->is_int()) {
     // The <channel_a and <channel_b values come with the init message
-    int chA = encData["<channel_a"];
-    int chB = encData["<channel_b"];
+    int chA = jchA->get_int();
+    int chB = jchB->get_int();
 
     if ((chA == 4 && chB == 5) || (chA == 5 && chB == 4)) {
       m_encoder_channel_map.emplace(0, deviceId);
@@ -302,9 +350,14 @@ void XRP::ReadGyroTag(std::span<const uint8_t> packet) {
   wpi::util::json gyroJson;
   gyroJson["type"] = "Gyro";
   gyroJson["device"] = m_gyro_name;
-  gyroJson["data"] = {{">rate_x", rate_x},   {">rate_y", rate_y},
-                      {">rate_z", rate_z},   {">angle_x", angle_x},
-                      {">angle_y", angle_y}, {">angle_z", angle_z}};
+  auto data = wpi::util::json::object();
+  data[">rate_x"] = rate_x;
+  data[">rate_y"] = rate_y;
+  data[">rate_z"] = rate_z;
+  data[">angle_x"] = angle_x;
+  data[">angle_y"] = angle_y;
+  data[">angle_z"] = angle_z;
+  gyroJson["data"] = std::move(data);
 
   // Update WPILib
   m_wpilib_update_func(gyroJson);
@@ -318,7 +371,7 @@ void XRP::ReadDIOTag(std::span<const uint8_t> packet) {
   wpi::util::json dioJson;
   dioJson["type"] = "DIO";
   dioJson["device"] = std::to_string(packet[2]);
-  dioJson["data"] = {{"<>value", packet[3] == 1}};
+  dioJson["data"] = wpi::util::json::object("<>value", packet[3] == 1);
 
   m_wpilib_update_func(dioJson);
 }
@@ -348,7 +401,7 @@ void XRP::ReadEncoderTag(std::span<const uint8_t> packet) {
   wpi::util::json encJson;
   encJson["type"] = "Encoder";
   encJson["device"] = std::to_string(wpilibEncoderChannel);
-  encJson["data"] = {{">count", count}};
+  encJson["data"] = wpi::util::json::object(">count", count);
 
   if (containsPeriod) {
     // Older versions of XRP firmware do not provide Encoder Period.
@@ -375,8 +428,7 @@ void XRP::ReadEncoderTag(std::span<const uint8_t> packet) {
       period = -period;
     }
 
-    encJson["data"].push_back(
-        {wpi::util::json(">period"), wpi::util::json(period)});
+    encJson["data"].emplace_back(wpi::util::json::object(">period", period));
   }
 
   m_wpilib_update_func(encJson);
@@ -396,7 +448,7 @@ void XRP::ReadAnalogTag(std::span<const uint8_t> packet) {
   wpi::util::json analogJson;
   analogJson["type"] = "AI";
   analogJson["device"] = std::to_string(analogId);
-  analogJson["data"] = {{">voltage", voltage}};
+  analogJson["data"] = wpi::util::json::object(">voltage", voltage);
 
   m_wpilib_update_func(analogJson);
 }
diff --git a/simulation/halsim_xrp/src/main/native/include/wpi/halsim/xrp/HALSimXRP.hpp b/simulation/halsim_xrp/src/main/native/include/wpi/halsim/xrp/HALSimXRP.hpp
index 2c234ac004..3badf135ec 100644
--- a/simulation/halsim_xrp/src/main/native/include/wpi/halsim/xrp/HALSimXRP.hpp
+++ b/simulation/halsim_xrp/src/main/native/include/wpi/halsim/xrp/HALSimXRP.hpp
@@ -18,7 +18,10 @@
 #include "wpi/net/uv/Loop.hpp"
 #include "wpi/net/uv/Timer.hpp"
 #include "wpi/net/uv/Udp.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpilibxrp {
 
diff --git a/simulation/halsim_xrp/src/main/native/include/wpi/halsim/xrp/XRP.hpp b/simulation/halsim_xrp/src/main/native/include/wpi/halsim/xrp/XRP.hpp
index 2cb0af2e93..5d5b1a2bde 100644
--- a/simulation/halsim_xrp/src/main/native/include/wpi/halsim/xrp/XRP.hpp
+++ b/simulation/halsim_xrp/src/main/native/include/wpi/halsim/xrp/XRP.hpp
@@ -10,7 +10,6 @@
 #include <string>
 
 #include "wpi/net/raw_uv_ostream.hpp"
-#include "wpi/util/json_fwd.hpp"
 
 #define XRP_TAG_MOTOR 0x12
 #define XRP_TAG_SERVO 0x13
@@ -20,6 +19,10 @@
 #define XRP_TAG_ACCEL 0x17
 #define XRP_TAG_ENCODER 0x18
 
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
+
 namespace wpilibxrp {
 
 using WPILibUpdateFunc = std::function<void(const wpi::util::json&)>;
diff --git a/tools/sysid/src/main/native/cpp/view/Analyzer.cpp b/tools/sysid/src/main/native/cpp/view/Analyzer.cpp
index a5d8e0fd59..afad133483 100644
--- a/tools/sysid/src/main/native/cpp/view/Analyzer.cpp
+++ b/tools/sysid/src/main/native/cpp/view/Analyzer.cpp
@@ -70,9 +70,6 @@ void Analyzer::UpdateFeedforwardGains() {
   } catch (const AnalysisManager::FileReadingError& e) {
     m_state = AnalyzerState::kFileError;
     HandleError(e.what());
-  } catch (const wpi::util::json::exception& e) {
-    m_state = AnalyzerState::kFileError;
-    HandleError(e.what());
   } catch (const std::exception& e) {
     m_state = AnalyzerState::kFileError;
     HandleError(e.what());
@@ -298,9 +295,6 @@ void Analyzer::PrepareData() {
   } catch (const AnalysisManager::FileReadingError& e) {
     m_state = AnalyzerState::kFileError;
     HandleError(e.what());
-  } catch (const wpi::util::json::exception& e) {
-    m_state = AnalyzerState::kFileError;
-    HandleError(e.what());
   } catch (const std::exception& e) {
     m_state = AnalyzerState::kFileError;
     HandleError(e.what());
diff --git a/tools/wpical/src/main/native/cpp/WPIcal.cpp b/tools/wpical/src/main/native/cpp/WPIcal.cpp
index 78740c6238..b145f66fa8 100644
--- a/tools/wpical/src/main/native/cpp/WPIcal.cpp
+++ b/tools/wpical/src/main/native/cpp/WPIcal.cpp
@@ -3,7 +3,6 @@
 // the WPILib BSD license file in the root directory of this project.
 
 #include <filesystem>
-#include <fstream>
 #include <map>
 #include <memory>
 #include <optional>
@@ -27,7 +26,10 @@
 #include "wpi/gui/wpigui.hpp"
 #include "wpi/gui/wpigui_openurl.hpp"
 #include "wpi/math/util/MathUtil.hpp"
+#include "wpi/util/MemoryBuffer.hpp"
+#include "wpi/util/fs.hpp"
 #include "wpi/util/json.hpp"
+#include "wpi/util/raw_ostream.hpp"
 
 namespace gui = wpi::gui;
 
@@ -175,14 +177,26 @@ void CameraCalibrationSelectorButton(const char* text,
   if (selector && selector->ready(0)) {
     auto selectedFiles = selector->result();
     if (!selectedFiles.empty()) {
+      auto fileBuffer = wpi::util::MemoryBuffer::GetFile(selectedFiles[0]);
+      if (!fileBuffer) {
+        goto err;
+      }
+      auto buffer = fileBuffer.value()->GetCharBuffer();
+      auto j = wpi::util::json::parse({buffer.data(), buffer.size()});
+      if (!j) {
+        goto err;
+      }
       try {
-        cameraModel = wpi::util::json::parse(std::ifstream(selectedFiles[0]))
-                          .get<wpical::CameraModel>();
+        cameraModel = j->get<wpical::CameraModel>();
       } catch (...) {
-        ImGui::SetNextWindowSize(ImVec2(600, 400), ImGuiCond_Always);
-        ImGui::OpenPopup("Camera Calibration Loading Error");
+        goto err;
       }
     }
+    goto done;
+  err:
+    ImGui::SetNextWindowSize(ImVec2(600, 400), ImGuiCond_Always);
+    ImGui::OpenPopup("Camera Calibration Loading Error");
+  done:
     selector.reset();
   }
 }
@@ -199,15 +213,29 @@ void FieldSelectorButton(const char* text,
     auto selectedFiles = selector->result();
     if (!selectedFiles.empty()) {
       std::string idealLayoutPath = selectedFiles[0];
+      auto fileBuffer = wpi::util::MemoryBuffer::GetFile(idealLayoutPath);
+      if (!fileBuffer) {
+        gInvalidLayoutPath = idealLayoutPath;
+        goto err;
+      }
+      auto buffer = fileBuffer.value()->GetCharBuffer();
+      auto j = wpi::util::json::parse({buffer.data(), buffer.size()});
+      if (!j) {
+        gInvalidLayoutPath = idealLayoutPath;
+        goto err;
+      }
       try {
-        layout = wpi::util::json::parse(std::ifstream(idealLayoutPath))
-                     .get<wpi::apriltag::AprilTagFieldLayout>();
+        layout = j->get<wpi::apriltag::AprilTagFieldLayout>();
       } catch (...) {
         gInvalidLayoutPath = idealLayoutPath;
-        ImGui::SetNextWindowSize(ImVec2(600, 400), ImGuiCond_Always);
-        ImGui::OpenPopup("AprilTag Field Layout Loading Error");
+        goto err;
       }
     }
+    goto done;
+  err:
+    ImGui::SetNextWindowSize(ImVec2(600, 400), ImGuiCond_Always);
+    ImGui::OpenPopup("AprilTag Field Layout Loading Error");
+  done:
     selector.reset();
   }
   if (layout.GetTags().size() > 0) {
@@ -226,11 +254,18 @@ void SaveCalibratedField(const wpi::apriltag::AprilTagFieldLayout& field,
   static std::string saveDir;
   ProcessDirectorySelector(saveDirSelector, saveDir);
   if (!saveDir.empty()) {
-    std::ofstream out(saveDir + "/" + outputName + ".json");
-    out << wpi::util::json{field}.dump(4);
+    std::error_code ec;
+    wpi::util::raw_fd_ostream out(saveDir + "/" + outputName + ".json", ec,
+                                  fs::OF_Text);
+    if (!ec) {
+      wpi::util::json{field}.marshal(out, true, 4);
+    }
 
-    std::ofstream fmap(saveDir + "/" + outputName + ".fmap");
-    fmap << wpi::util::json{fmap::Fieldmap(field)}.dump(4);
+    wpi::util::raw_fd_ostream fmap(saveDir + "/" + outputName + ".fmap", ec,
+                                   fs::OF_Text);
+    if (!ec) {
+      wpi::util::json{fmap::Fieldmap(field)}.marshal(fmap, true, 4);
+    }
 
     saveDir.clear();
   }
@@ -286,8 +321,12 @@ void CalibrateCamera() {
         std::filesystem::path myPath(cameraVideoPath);
         auto outputPath = myPath.parent_path() / "cameracalibration.json";
 
-        std::ofstream output_file(outputPath);
-        output_file << wpi::util::json(gCameraModel).dump(4) << std::endl;
+        std::error_code ec;
+        wpi::util::raw_fd_ostream output_file(outputPath.string(), ec,
+                                              fs::OF_Text);
+        if (!ec) {
+          wpi::util::json{gCameraModel}.marshal(output_file, true, 4);
+        }
         ImGui::CloseCurrentPopup();
         calibrating = false;
       } else if (!videoProcessor->IsFinished()) {
@@ -350,16 +389,30 @@ void CombineCalibrations() {
       if (!selectedFiles.empty()) {
         std::map<std::string, wpi::apriltag::AprilTagFieldLayout> fieldLayouts;
         for (auto& path : selectedFiles) {
+          auto fileBuffer = wpi::util::MemoryBuffer::GetFile(path);
+          if (!fileBuffer) {
+            gInvalidLayoutPath = path;
+            goto err;
+          }
+          auto buffer = fileBuffer.value()->GetCharBuffer();
+          auto j = wpi::util::json::parse({buffer.data(), buffer.size()});
+          if (!j) {
+            gInvalidLayoutPath = path;
+            goto err;
+          }
           try {
-            fieldLayouts.emplace(
-                path, wpi::util::json::parse(std::ifstream(path))
-                          .get<wpi::apriltag::AprilTagFieldLayout>());
+            fieldLayouts.emplace(path,
+                                 j->get<wpi::apriltag::AprilTagFieldLayout>());
           } catch (...) {
             gInvalidLayoutPath = path;
-            ImGui::SetNextWindowSize(ImVec2(600, 400), ImGuiCond_Always);
-            ImGui::OpenPopup("AprilTag Field Layout Loading Error");
+            goto err;
           }
         }
+        goto good;
+      err:
+        ImGui::SetNextWindowSize(ImVec2(600, 400), ImGuiCond_Always);
+        ImGui::OpenPopup("AprilTag Field Layout Loading Error");
+      good:
         calibratedFieldLayouts = fieldLayouts;
       }
       calibratedFieldLayoutMultiselector.reset();
diff --git a/tools/wpical/src/main/native/cpp/cameracalibration.cpp b/tools/wpical/src/main/native/cpp/cameracalibration.cpp
index f753e1d6b2..3f7aceaa6e 100644
--- a/tools/wpical/src/main/native/cpp/cameracalibration.cpp
+++ b/tools/wpical/src/main/native/cpp/cameracalibration.cpp
@@ -306,47 +306,71 @@ void to_json(wpi::util::json& json, const CameraModel& cameraModel) {
       cameraModel.distortionCoefficients.data(),
       cameraModel.distortionCoefficients.data() +
           cameraModel.distortionCoefficients.size());
-  json = {{"camera_matrix", cameraMatrix},
-          {"distortion_coefficients", distortionCoefficients},
-          {"avg_reprojection_error", cameraModel.avgReprojectionError}};
+  json = wpi::util::json::object();
+  json["camera_matrix"] = cameraMatrix;
+  json["distortion_coefficients"] = distortionCoefficients;
+  json["avg_reprojection_error"] = cameraModel.avgReprojectionError;
 }
 
 void from_json(const wpi::util::json& json, CameraModel& cameraModel) {
   bool isCalibdb = json.contains("camera");
   Eigen::Matrix3d cameraMatrix;
   std::vector<double> distortionCoeffs;
-  auto mat = json.at("camera_matrix");
-  auto distortionCoefficients = json.at("distortion_coefficients");
+  auto jmat = json.at("camera_matrix");
+  auto jdistortionCoefficients = json.at("distortion_coefficients");
   if (isCalibdb) {
     // OpenCV format has data key
-    if (mat.contains("data")) {
-      auto data = mat.at("data").get<std::vector<double>>();
+    if (auto jdata = jmat.lookup("data")) {
+      auto& arr = jdata->get_array();
+      std::vector<double> data;
+      data.reserve(arr.size());
+      for (const auto& item : arr) {
+        data.push_back(item.get_number());
+      }
       cameraMatrix = Eigen::Matrix<double, 3, 3, Eigen::RowMajor>{data.data()};
     } else {
       for (int i = 0; i < cameraMatrix.rows(); i++) {
+        auto& jcols = jmat.at(i);
         for (int j = 0; j < cameraMatrix.cols(); j++) {
-          cameraMatrix(i, j) = mat[i][j];
+          cameraMatrix(i, j) = jcols.at(j).get_number();
         }
       }
     }
 
     // OpenCV format has data key
-    if (distortionCoefficients.contains("data")) {
-      distortionCoeffs =
-          distortionCoefficients.at("data").get<std::vector<double>>();
+    wpi::util::json::array_t* arr;
+    if (auto jdata = jdistortionCoefficients.lookup("data")) {
+      arr = &jdata->get_array();
     } else {
-      distortionCoeffs = distortionCoefficients.get<std::vector<double>>();
+      arr = &jdistortionCoefficients.get_array();
+    }
+    distortionCoeffs.reserve(arr->size());
+    for (const auto& item : *arr) {
+      distortionCoeffs.push_back(item.get_number());
     }
   } else {
-    cameraMatrix = Eigen::Matrix<double, 3, 3, Eigen::RowMajor>{
-        mat.get<std::vector<double>>().data()};
-    distortionCoeffs = distortionCoefficients.get<std::vector<double>>();
+    {
+      auto& arr = jmat.get_array();
+      std::vector<double> data;
+      data.reserve(arr.size());
+      for (const auto& item : arr) {
+        data.push_back(item.get_number());
+      }
+      cameraMatrix = Eigen::Matrix<double, 3, 3, Eigen::RowMajor>{data.data()};
+    }
+    {
+      auto& arr = jdistortionCoefficients.get_array();
+      distortionCoeffs.reserve(arr.size());
+      for (const auto& item : arr) {
+        distortionCoeffs.push_back(item.get_number());
+      }
+    }
   }
   // CalibDB generates JSONs with 5 values. Just zero out the remaining 3 to get
   // it to 8
   distortionCoeffs.resize(8, 0);
   cameraModel = {cameraMatrix,
                  Eigen::Matrix<double, 8, 1>{distortionCoeffs.data()},
-                 json.at("avg_reprojection_error")};
+                 json.at("avg_reprojection_error").get_number()};
 }
 }  // namespace wpical
diff --git a/tools/wpical/src/main/native/cpp/fmap.cpp b/tools/wpical/src/main/native/cpp/fmap.cpp
index c584eb2cd2..181558d415 100644
--- a/tools/wpical/src/main/native/cpp/fmap.cpp
+++ b/tools/wpical/src/main/native/cpp/fmap.cpp
@@ -29,25 +29,39 @@ Fieldmap::Fieldmap(const wpi::apriltag::AprilTagFieldLayout& layout)
 }
 
 void fmap::to_json(wpi::util::json& json, const Fiducial& layout) {
-  json = {{"family", layout.family},
-          {"id", layout.id},
-          {"size", layout.size},
-          {"transform", std::vector<double>{layout.transform.data(),
-                                            layout.transform.data() +
-                                                layout.transform.size()}},
-          {"unique", layout.unique}};
+  json = wpi::util::json::object();
+  json["family"] = layout.family;
+  json["id"] = layout.id;
+  json["size"] = layout.size;
+  json["transform"] =
+      std::vector<double>{layout.transform.data(),
+                          layout.transform.data() + layout.transform.size()};
+  json["unique"] = layout.unique;
 }
 
 void fmap::from_json(const wpi::util::json& json, Fiducial& layout) {
-  auto vec = json.at("transform").get<std::vector<double>>();
-  layout = {json.at("family"), json.at("id"), json.at("size"),
-            Eigen::Matrix4d{vec.data()}, json.at("unique")};
+  auto& arr = json.at("transform").get_array();
+  std::vector<double> vec;
+  vec.reserve(arr.size());
+  for (auto& elem : arr) {
+    vec.push_back(elem.get_number());
+  }
+  layout = {json.at("family").get_string(),
+            static_cast<int>(json.at("id").get_int()),
+            json.at("size").get_number(), Eigen::Matrix4d{vec.data()},
+            static_cast<int>(json.at("unique").get_int())};
 }
 
 void fmap::to_json(wpi::util::json& json, const Fieldmap& layout) {
-  json = {{"type", "frc"}, {"fiducials", layout.fiducials}};
+  json = wpi::util::json::object("type", "frc", "fiducials", layout.fiducials);
 }
 
 void fmap::from_json(const wpi::util::json& json, Fieldmap& layout) {
-  layout = {json.at("type"), json.at("fiducials")};
+  auto& arr = json.at("fiducials").get_array();
+  std::vector<Fiducial> fiducials;
+  fiducials.reserve(arr.size());
+  for (auto& elem : arr) {
+    fiducials.emplace_back(elem.get<Fiducial>());
+  }
+  layout = {json.at("type").get_string(), fiducials};
 }
diff --git a/tools/wpical/src/test/native/cpp/test_calibrate.cpp b/tools/wpical/src/test/native/cpp/test_calibrate.cpp
index a5b582034c..fd7cf873da 100644
--- a/tools/wpical/src/test/native/cpp/test_calibrate.cpp
+++ b/tools/wpical/src/test/native/cpp/test_calibrate.cpp
@@ -2,7 +2,6 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-#include <fstream>
 #include <optional>
 #include <string>
 
@@ -13,7 +12,10 @@
 #include "path_lookup.hpp"
 #include "wpi/apriltag/AprilTagFieldLayout.hpp"
 #include "wpi/apriltag/AprilTagFields.hpp"
+#include "wpi/util/MemoryBuffer.hpp"
+#include "wpi/util/fs.hpp"
 #include "wpi/util/json.hpp"
+#include "wpi/util/raw_ostream.hpp"
 
 const std::string projectRootPath = PROJECT_ROOT_PATH;
 
@@ -42,8 +44,10 @@ TEST(CameraCalibrationTest, Typical) {
   }
   auto ret = calibrator.GetCameraModel();
   EXPECT_NE(ret, std::nullopt);
-  std::ofstream output_file(calSavePath + "/cameracalibration.json");
-  output_file << wpi::util::json(ret.value()).dump(4) << std::endl;
+  std::error_code ec;
+  wpi::util::raw_fd_ostream output_file(calSavePath + "/cameracalibration.json",
+                                        ec, fs::OF_Text);
+  wpi::util::json(ret.value()).marshal(output_file, true, 4);
 }
 
 TEST(CameraCalibrationTest, Atypical) {
@@ -58,8 +62,10 @@ TEST(CameraCalibrationTest, Atypical) {
 }
 
 TEST(FieldCalibrationTest, Typical) {
-  auto model = wpi::util::json::parse(
-                   std::ifstream(calSavePath + "/cameracalibration.json"))
+  auto buffer =
+      wpi::util::MemoryBuffer::GetFile(calSavePath + "/cameracalibration.json");
+  auto buf = buffer.value()->GetCharBuffer();
+  auto model = wpi::util::json::parse_or_throw({buf.data(), buf.size()})
                    .get<wpical::CameraModel>();
   auto ret =
       wpical::calibrate(LookupPath(projectRootPath + videoLocation), model,
@@ -80,8 +86,10 @@ TEST(FieldCalibrationTest, Atypical_Bad_Camera_Model) {
 }
 
 TEST(FieldCalibrationTest, Atypical_Bad_Field_Layout) {
-  auto model = wpi::util::json::parse(
-                   std::ifstream(calSavePath + "/cameracalibration.json"))
+  auto buffer =
+      wpi::util::MemoryBuffer::GetFile(calSavePath + "/cameracalibration.json");
+  auto buf = buffer.value()->GetCharBuffer();
+  auto model = wpi::util::json::parse_or_throw({buf.data(), buf.size()})
                    .get<wpical::CameraModel>();
   auto ret =
       wpical::calibrate(LookupPath(projectRootPath + videoLocation), model,
@@ -90,8 +98,10 @@ TEST(FieldCalibrationTest, Atypical_Bad_Field_Layout) {
 }
 
 TEST(FieldCalibrationTest, Atypical_Bad_Input_Directory) {
-  auto model = wpi::util::json::parse(
-                   std::ifstream(calSavePath + "/cameracalibration.json"))
+  auto buffer =
+      wpi::util::MemoryBuffer::GetFile(calSavePath + "/cameracalibration.json");
+  auto buf = buffer.value()->GetCharBuffer();
+  auto model = wpi::util::json::parse_or_throw({buf.data(), buf.size()})
                    .get<wpical::CameraModel>();
   auto ret =
       wpical::calibrate(LookupPath(projectRootPath), model,
@@ -102,8 +112,10 @@ TEST(FieldCalibrationTest, Atypical_Bad_Input_Directory) {
 }
 
 TEST(FieldCalibrationTest, Atypical_Bad_Pinned_Tag) {
-  auto model = wpi::util::json::parse(
-                   std::ifstream(calSavePath + "/cameracalibration.json"))
+  auto buffer =
+      wpi::util::MemoryBuffer::GetFile(calSavePath + "/cameracalibration.json");
+  auto buf = buffer.value()->GetCharBuffer();
+  auto model = wpi::util::json::parse_or_throw({buf.data(), buf.size()})
                    .get<wpical::CameraModel>();
   auto ret =
       wpical::calibrate(LookupPath(projectRootPath + videoLocation), model,
@@ -114,8 +126,10 @@ TEST(FieldCalibrationTest, Atypical_Bad_Pinned_Tag) {
 }
 
 TEST(FieldCalibrationTest, Atypical_Bad_Pinned_Tag_Negative) {
-  auto model = wpi::util::json::parse(
-                   std::ifstream(calSavePath + "/cameracalibration.json"))
+  auto buffer =
+      wpi::util::MemoryBuffer::GetFile(calSavePath + "/cameracalibration.json");
+  auto buf = buffer.value()->GetCharBuffer();
+  auto model = wpi::util::json::parse_or_throw({buf.data(), buf.size()})
                    .get<wpical::CameraModel>();
   auto ret =
       wpical::calibrate(LookupPath(projectRootPath + videoLocation), model,
diff --git a/wpilibc/src/main/native/cpp/driverstation/DriverStation.cpp b/wpilibc/src/main/native/cpp/driverstation/DriverStation.cpp
index 2e07237044..b1d22f4aea 100644
--- a/wpilibc/src/main/native/cpp/driverstation/DriverStation.cpp
+++ b/wpilibc/src/main/native/cpp/driverstation/DriverStation.cpp
@@ -87,10 +87,8 @@ struct MatchDataSender {
   std::shared_ptr<wpi::nt::NetworkTable> table =
       wpi::nt::NetworkTableInstance::GetDefault().GetTable("FMSInfo");
   MatchDataSenderEntry<wpi::nt::StringTopic> typeMetaData{
-      table,
-      ".type",
-      kSmartDashboardType,
-      {{"SmartDashboard", kSmartDashboardType}}};
+      table, ".type", kSmartDashboardType,
+      wpi::util::json::object("SmartDashboard", kSmartDashboardType)};
   MatchDataSenderEntry<wpi::nt::StringTopic> gameData{table, "GameData", ""};
   MatchDataSenderEntry<wpi::nt::StringTopic> eventName{table, "EventName", ""};
   MatchDataSenderEntry<wpi::nt::IntegerTopic> matchNumber{table, "MatchNumber",
diff --git a/wpilibc/src/main/native/cpp/smartdashboard/MechanismLigament2d.cpp b/wpilibc/src/main/native/cpp/smartdashboard/MechanismLigament2d.cpp
index 62a34b1864..a1d150977a 100644
--- a/wpilibc/src/main/native/cpp/smartdashboard/MechanismLigament2d.cpp
+++ b/wpilibc/src/main/native/cpp/smartdashboard/MechanismLigament2d.cpp
@@ -29,7 +29,7 @@ void MechanismLigament2d::UpdateEntries(
     std::shared_ptr<wpi::nt::NetworkTable> table) {
   m_typePub = table->GetStringTopic(".type").PublishEx(
       wpi::nt::StringTopic::TYPE_STRING,
-      {{"SmartDashboard", kSmartDashboardType}});
+      wpi::util::json::object("SmartDashboard", kSmartDashboardType));
   m_typePub.Set(kSmartDashboardType);
 
   m_colorEntry = table->GetStringTopic("color").GetEntry("");
diff --git a/wpilibc/src/main/native/cpp/smartdashboard/SendableBuilderImpl.cpp b/wpilibc/src/main/native/cpp/smartdashboard/SendableBuilderImpl.cpp
index 808c4facb1..d619a07490 100644
--- a/wpilibc/src/main/native/cpp/smartdashboard/SendableBuilderImpl.cpp
+++ b/wpilibc/src/main/native/cpp/smartdashboard/SendableBuilderImpl.cpp
@@ -85,7 +85,8 @@ void SendableBuilderImpl::ClearProperties() {
 void SendableBuilderImpl::SetSmartDashboardType(std::string_view type) {
   if (!m_typePublisher) {
     m_typePublisher = m_table->GetStringTopic(".type").PublishEx(
-        wpi::nt::StringTopic::TYPE_STRING, {{"SmartDashboard", type}});
+        wpi::nt::StringTopic::TYPE_STRING,
+        wpi::util::json::object("SmartDashboard", type));
   }
   m_typePublisher.Set(type);
 }
diff --git a/wpilibc/src/main/native/cpp/util/Preferences.cpp b/wpilibc/src/main/native/cpp/util/Preferences.cpp
index f599a4a53b..87518937a9 100644
--- a/wpilibc/src/main/native/cpp/util/Preferences.cpp
+++ b/wpilibc/src/main/native/cpp/util/Preferences.cpp
@@ -32,7 +32,7 @@ struct Instance {
   wpi::nt::StringPublisher typePublisher{
       table->GetStringTopic(".type").PublishEx(
           wpi::nt::StringTopic::TYPE_STRING,
-          {{"SmartDashboard", kSmartDashboardType}})};
+          wpi::util::json::object("SmartDashboard", kSmartDashboardType))};
   wpi::nt::MultiSubscriber tableSubscriber{
       wpi::nt::NetworkTableInstance::GetDefault(),
       {{fmt::format("{}/", table->GetPath())}}};
diff --git a/wpimath/src/main/native/cpp/geometry/Pose2d.cpp b/wpimath/src/main/native/cpp/geometry/Pose2d.cpp
index 7b05dfc51a..0c795203df 100644
--- a/wpimath/src/main/native/cpp/geometry/Pose2d.cpp
+++ b/wpimath/src/main/native/cpp/geometry/Pose2d.cpp
@@ -7,8 +7,9 @@
 #include "wpi/util/json.hpp"
 
 void wpi::math::to_json(wpi::util::json& json, const Pose2d& pose) {
-  json = wpi::util::json{{"translation", pose.Translation()},
-                         {"rotation", pose.Rotation()}};
+  json.set_object();
+  json["translation"] = pose.Translation();
+  json["rotation"] = pose.Rotation();
 }
 
 void wpi::math::from_json(const wpi::util::json& json, Pose2d& pose) {
diff --git a/wpimath/src/main/native/cpp/geometry/Pose3d.cpp b/wpimath/src/main/native/cpp/geometry/Pose3d.cpp
index bac9f9f21c..c1838a6ebe 100644
--- a/wpimath/src/main/native/cpp/geometry/Pose3d.cpp
+++ b/wpimath/src/main/native/cpp/geometry/Pose3d.cpp
@@ -7,8 +7,9 @@
 #include "wpi/util/json.hpp"
 
 void wpi::math::to_json(wpi::util::json& json, const Pose3d& pose) {
-  json = wpi::util::json{{"translation", pose.Translation()},
-                         {"rotation", pose.Rotation()}};
+  json.set_object();
+  json["translation"] = pose.Translation();
+  json["rotation"] = pose.Rotation();
 }
 
 void wpi::math::from_json(const wpi::util::json& json, Pose3d& pose) {
diff --git a/wpimath/src/main/native/cpp/geometry/Quaternion.cpp b/wpimath/src/main/native/cpp/geometry/Quaternion.cpp
index b2cecfe5dc..c2d4e1779b 100644
--- a/wpimath/src/main/native/cpp/geometry/Quaternion.cpp
+++ b/wpimath/src/main/native/cpp/geometry/Quaternion.cpp
@@ -7,14 +7,14 @@
 #include "wpi/util/json.hpp"
 
 void wpi::math::to_json(wpi::util::json& json, const Quaternion& quaternion) {
-  json = wpi::util::json{{"W", quaternion.W()},
-                         {"X", quaternion.X()},
-                         {"Y", quaternion.Y()},
-                         {"Z", quaternion.Z()}};
+  json.set_object();
+  json["W"] = quaternion.W();
+  json["X"] = quaternion.X();
+  json["Y"] = quaternion.Y();
+  json["Z"] = quaternion.Z();
 }
 
 void wpi::math::from_json(const wpi::util::json& json, Quaternion& quaternion) {
-  quaternion =
-      Quaternion{json.at("W").get<double>(), json.at("X").get<double>(),
-                 json.at("Y").get<double>(), json.at("Z").get<double>()};
+  quaternion = Quaternion{json.at("W").get_number(), json.at("X").get_number(),
+                          json.at("Y").get_number(), json.at("Z").get_number()};
 }
diff --git a/wpimath/src/main/native/cpp/geometry/Rotation2d.cpp b/wpimath/src/main/native/cpp/geometry/Rotation2d.cpp
index 3c3b195def..04a551cac2 100644
--- a/wpimath/src/main/native/cpp/geometry/Rotation2d.cpp
+++ b/wpimath/src/main/native/cpp/geometry/Rotation2d.cpp
@@ -7,9 +7,9 @@
 #include "wpi/util/json.hpp"
 
 void wpi::math::to_json(wpi::util::json& json, const Rotation2d& rotation) {
-  json = wpi::util::json{{"radians", rotation.Radians().value()}};
+  json = wpi::util::json::object("radians", rotation.Radians().value());
 }
 
 void wpi::math::from_json(const wpi::util::json& json, Rotation2d& rotation) {
-  rotation = Rotation2d{wpi::units::radian_t{json.at("radians").get<double>()}};
+  rotation = Rotation2d{wpi::units::radian_t{json.at("radians").get_number()}};
 }
diff --git a/wpimath/src/main/native/cpp/geometry/Rotation3d.cpp b/wpimath/src/main/native/cpp/geometry/Rotation3d.cpp
index 5b81b54666..747374ba5b 100644
--- a/wpimath/src/main/native/cpp/geometry/Rotation3d.cpp
+++ b/wpimath/src/main/native/cpp/geometry/Rotation3d.cpp
@@ -7,7 +7,7 @@
 #include "wpi/util/json.hpp"
 
 void wpi::math::to_json(wpi::util::json& json, const Rotation3d& rotation) {
-  json = wpi::util::json{{"quaternion", rotation.GetQuaternion()}};
+  json = wpi::util::json::object("quaternion", rotation.GetQuaternion());
 }
 
 void wpi::math::from_json(const wpi::util::json& json, Rotation3d& rotation) {
diff --git a/wpimath/src/main/native/cpp/geometry/Translation2d.cpp b/wpimath/src/main/native/cpp/geometry/Translation2d.cpp
index 633a823637..b7b7e5bf3e 100644
--- a/wpimath/src/main/native/cpp/geometry/Translation2d.cpp
+++ b/wpimath/src/main/native/cpp/geometry/Translation2d.cpp
@@ -8,12 +8,13 @@
 
 void wpi::math::to_json(wpi::util::json& json,
                         const Translation2d& translation) {
-  json = wpi::util::json{{"x", translation.X().value()},
-                         {"y", translation.Y().value()}};
+  json.set_object();
+  json["x"] = translation.X().value();
+  json["y"] = translation.Y().value();
 }
 
 void wpi::math::from_json(const wpi::util::json& json,
                           Translation2d& translation) {
-  translation = Translation2d{wpi::units::meter_t{json.at("x").get<double>()},
-                              wpi::units::meter_t{json.at("y").get<double>()}};
+  translation = Translation2d{wpi::units::meter_t{json.at("x").get_number()},
+                              wpi::units::meter_t{json.at("y").get_number()}};
 }
diff --git a/wpimath/src/main/native/cpp/geometry/Translation3d.cpp b/wpimath/src/main/native/cpp/geometry/Translation3d.cpp
index 4b777e32b1..c82fdb961e 100644
--- a/wpimath/src/main/native/cpp/geometry/Translation3d.cpp
+++ b/wpimath/src/main/native/cpp/geometry/Translation3d.cpp
@@ -8,14 +8,15 @@
 
 void wpi::math::to_json(wpi::util::json& json,
                         const Translation3d& translation) {
-  json = wpi::util::json{{"x", translation.X().value()},
-                         {"y", translation.Y().value()},
-                         {"z", translation.Z().value()}};
+  json.set_object();
+  json["x"] = translation.X().value();
+  json["y"] = translation.Y().value();
+  json["z"] = translation.Z().value();
 }
 
 void wpi::math::from_json(const wpi::util::json& json,
                           Translation3d& translation) {
-  translation = Translation3d{wpi::units::meter_t{json.at("x").get<double>()},
-                              wpi::units::meter_t{json.at("y").get<double>()},
-                              wpi::units::meter_t{json.at("z").get<double>()}};
+  translation = Translation3d{wpi::units::meter_t{json.at("x").get_number()},
+                              wpi::units::meter_t{json.at("y").get_number()},
+                              wpi::units::meter_t{json.at("z").get_number()}};
 }
diff --git a/wpimath/src/main/native/cpp/trajectory/Trajectory.cpp b/wpimath/src/main/native/cpp/trajectory/Trajectory.cpp
index d3c0336b72..9de19f7734 100644
--- a/wpimath/src/main/native/cpp/trajectory/Trajectory.cpp
+++ b/wpimath/src/main/native/cpp/trajectory/Trajectory.cpp
@@ -9,20 +9,21 @@
 using namespace wpi::math;
 
 void wpi::math::to_json(wpi::util::json& json, const Trajectory::State& state) {
-  json = wpi::util::json{{"time", state.t.value()},
-                         {"velocity", state.velocity.value()},
-                         {"acceleration", state.acceleration.value()},
-                         {"pose", state.pose},
-                         {"curvature", state.curvature.value()}};
+  json.set_object();
+  json["time"] = state.t.value();
+  json["velocity"] = state.velocity.value();
+  json["acceleration"] = state.acceleration.value();
+  json["pose"] = state.pose;
+  json["curvature"] = state.curvature.value();
 }
 
 void wpi::math::from_json(const wpi::util::json& json,
                           Trajectory::State& state) {
   state.pose = json.at("pose").get<Pose2d>();
-  state.t = wpi::units::second_t{json.at("time").get<double>()};
+  state.t = wpi::units::second_t{json.at("time").get_number()};
   state.velocity =
-      wpi::units::meters_per_second_t{json.at("velocity").get<double>()};
+      wpi::units::meters_per_second_t{json.at("velocity").get_number()};
   state.acceleration = wpi::units::meters_per_second_squared_t{
-      json.at("acceleration").get<double>()};
-  state.curvature = wpi::units::curvature_t{json.at("curvature").get<double>()};
+      json.at("acceleration").get_number()};
+  state.curvature = wpi::units::curvature_t{json.at("curvature").get_number()};
 }
diff --git a/wpimath/src/main/native/include/wpi/math/geometry/Pose2d.hpp b/wpimath/src/main/native/include/wpi/math/geometry/Pose2d.hpp
index d716def254..b7a0c95919 100644
--- a/wpimath/src/main/native/include/wpi/math/geometry/Pose2d.hpp
+++ b/wpimath/src/main/native/include/wpi/math/geometry/Pose2d.hpp
@@ -15,7 +15,10 @@
 #include "wpi/math/geometry/Translation2d.hpp"
 #include "wpi/units/length.hpp"
 #include "wpi/util/SymbolExports.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::math {
 
diff --git a/wpimath/src/main/native/include/wpi/math/geometry/Pose3d.hpp b/wpimath/src/main/native/include/wpi/math/geometry/Pose3d.hpp
index c9f3b034f7..9414e1ca5a 100644
--- a/wpimath/src/main/native/include/wpi/math/geometry/Pose3d.hpp
+++ b/wpimath/src/main/native/include/wpi/math/geometry/Pose3d.hpp
@@ -16,7 +16,10 @@
 #include "wpi/math/geometry/Rotation3d.hpp"
 #include "wpi/math/geometry/Translation3d.hpp"
 #include "wpi/util/SymbolExports.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::math {
 
diff --git a/wpimath/src/main/native/include/wpi/math/geometry/Quaternion.hpp b/wpimath/src/main/native/include/wpi/math/geometry/Quaternion.hpp
index 14dcbae211..1e5980d8d8 100644
--- a/wpimath/src/main/native/include/wpi/math/geometry/Quaternion.hpp
+++ b/wpimath/src/main/native/include/wpi/math/geometry/Quaternion.hpp
@@ -10,7 +10,10 @@
 #include <gcem.hpp>
 
 #include "wpi/util/SymbolExports.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::math {
 
diff --git a/wpimath/src/main/native/include/wpi/math/geometry/Rotation2d.hpp b/wpimath/src/main/native/include/wpi/math/geometry/Rotation2d.hpp
index 3f64a2e14e..bdb2947e3a 100644
--- a/wpimath/src/main/native/include/wpi/math/geometry/Rotation2d.hpp
+++ b/wpimath/src/main/native/include/wpi/math/geometry/Rotation2d.hpp
@@ -15,7 +15,10 @@
 #include "wpi/units/angle.hpp"
 #include "wpi/util/StackTrace.hpp"
 #include "wpi/util/SymbolExports.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::math {
 
diff --git a/wpimath/src/main/native/include/wpi/math/geometry/Rotation3d.hpp b/wpimath/src/main/native/include/wpi/math/geometry/Rotation3d.hpp
index 513182bf62..82200c8b82 100644
--- a/wpimath/src/main/native/include/wpi/math/geometry/Rotation3d.hpp
+++ b/wpimath/src/main/native/include/wpi/math/geometry/Rotation3d.hpp
@@ -17,7 +17,10 @@
 #include "wpi/units/math.hpp"
 #include "wpi/util/MathExtras.hpp"
 #include "wpi/util/SymbolExports.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::math {
 
diff --git a/wpimath/src/main/native/include/wpi/math/geometry/Translation2d.hpp b/wpimath/src/main/native/include/wpi/math/geometry/Translation2d.hpp
index 1fd26d71a7..2c8d868c32 100644
--- a/wpimath/src/main/native/include/wpi/math/geometry/Translation2d.hpp
+++ b/wpimath/src/main/native/include/wpi/math/geometry/Translation2d.hpp
@@ -15,7 +15,10 @@
 #include "wpi/units/length.hpp"
 #include "wpi/units/math.hpp"
 #include "wpi/util/SymbolExports.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::math {
 
diff --git a/wpimath/src/main/native/include/wpi/math/geometry/Translation3d.hpp b/wpimath/src/main/native/include/wpi/math/geometry/Translation3d.hpp
index b44cbf3b60..26039566ca 100644
--- a/wpimath/src/main/native/include/wpi/math/geometry/Translation3d.hpp
+++ b/wpimath/src/main/native/include/wpi/math/geometry/Translation3d.hpp
@@ -16,7 +16,10 @@
 #include "wpi/units/length.hpp"
 #include "wpi/units/math.hpp"
 #include "wpi/util/SymbolExports.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::math {
 
diff --git a/wpimath/src/main/native/include/wpi/math/trajectory/Trajectory.hpp b/wpimath/src/main/native/include/wpi/math/trajectory/Trajectory.hpp
index e5cd3a6d49..8b65f0a957 100644
--- a/wpimath/src/main/native/include/wpi/math/trajectory/Trajectory.hpp
+++ b/wpimath/src/main/native/include/wpi/math/trajectory/Trajectory.hpp
@@ -17,7 +17,10 @@
 #include "wpi/units/velocity.hpp"
 #include "wpi/util/MathExtras.hpp"
 #include "wpi/util/SymbolExports.hpp"
-#include "wpi/util/json_fwd.hpp"
+
+namespace wpi::util {
+class json;
+}  // namespace wpi::util
 
 namespace wpi::math {
 /**
diff --git a/wpinet/src/main/native/cpp/DsClient.cpp b/wpinet/src/main/native/cpp/DsClient.cpp
index 3b81175ae9..05b8a8c9be 100644
--- a/wpinet/src/main/native/cpp/DsClient.cpp
+++ b/wpinet/src/main/native/cpp/DsClient.cpp
@@ -94,8 +94,8 @@ void DsClient::ParseJson() {
   WPI_DEBUG4(m_logger, "DsClient JSON: {}", m_json);
   unsigned int ip = 0;
   try {
-    ip = wpi::util::json::parse(m_json).at("robotIP").get<unsigned int>();
-  } catch (wpi::util::json::exception& e) {
+    ip = wpi::util::json::parse_or_throw(m_json).at("robotIP").get_int();
+  } catch (std::logic_error& e) {
     WPI_INFO(m_logger, "DsClient JSON error: {}", e.what());
     return;
   }
diff --git a/wpinet/src/main/native/cpp/WebServer.cpp b/wpinet/src/main/native/cpp/WebServer.cpp
index 0a0df5bf10..db437ae693 100644
--- a/wpinet/src/main/native/cpp/WebServer.cpp
+++ b/wpinet/src/main/native/cpp/WebServer.cpp
@@ -279,17 +279,17 @@ void MyHttpConnection::ProcessRequest() {
           bool subdir = entry.is_directory(ec);
           std::string name = entry.path().filename().string();
           if (subdir) {
-            dirs.emplace_back(wpi::util::json{{"name", std::move(name)}});
+            dirs.emplace_back(wpi::util::json::object("name", std::move(name)));
           } else {
             files.emplace_back(
-                wpi::util::json{{"name", std::move(name)},
-                                {"size", subdir ? 0 : entry.file_size(ec)}});
+                wpi::util::json::object("name", std::move(name), "size",
+                                        subdir ? 0 : entry.file_size(ec)));
           }
         }
         SendResponse(200, "OK", "text/json",
-                     wpi::util::json{{"dirs", std::move(dirs)},
-                                     {"files", std::move(files)}}
-                         .dump());
+                     wpi::util::json::object("dirs", std::move(dirs), "files",
+                                             std::move(files))
+                         .to_string());
       } else if (fs::exists(indexpath)) {
         SendFileResponse(200, "OK", GetMimeType("html"), indexpath,
                          "Content-Disposition: filename=\"index.html\"\r\n");
diff --git a/wpiutil/src/main/python/wpiutil/src/type_casters/wpi_json_type_caster.h b/wpiutil/src/main/python/wpiutil/src/type_casters/wpi_json_type_caster.h
index b10cddd3cc..c4e1086c1c 100644
--- a/wpiutil/src/main/python/wpiutil/src/type_casters/wpi_json_type_caster.h
+++ b/wpiutil/src/main/python/wpiutil/src/type_casters/wpi_json_type_caster.h
@@ -53,41 +53,46 @@ namespace pyjson
         {
             return py::none();
         }
-        else if (j.is_boolean())
+        else if (j.is_bool())
         {
-            return py::bool_(j.get<bool>());
+            return py::bool_(j.get_bool());
         }
-        else if (j.is_number_unsigned())
+        else if (j.is_int())
         {
-            return py::int_(j.get<number_unsigned_t>());
+            return py::int_(j.get_int());
         }
-        else if (j.is_number_integer())
+        else if (j.is_uint())
         {
-            return py::int_(j.get<number_integer_t>());
+            return py::int_(j.get_uint());
         }
-        else if (j.is_number_float())
+        else if (j.is_float())
         {
-            return py::float_(j.get<double>());
+            return py::float_(j.get_float());
+        }
+        else if (j.is_double())
+        {
+            return py::float_(j.get_double());
         }
         else if (j.is_string())
         {
-            return py::str(j.get<std::string>());
+            return py::str(j.get_string());
         }
         else if (j.is_array())
         {
-            py::list obj(j.size());
-            for (std::size_t i = 0; i < j.size(); i++)
+            auto& arr = j.get_array();
+            py::list obj(arr.size());
+            for (std::size_t i = 0; i < arr.size(); i++)
             {
-                obj[i] = from_json(j[i]);
+                obj[i] = from_json(arr[i]);
             }
             return std::move(obj);
         }
         else // Object
         {
             py::dict obj;
-            for (wpi::util::json::const_iterator it = j.cbegin(); it != j.cend(); ++it)
+            for (auto&& [key, value] : j.get_object())
             {
-                obj[py::str(it.key())] = from_json(it.value());
+                obj[py::str(key)] = from_json(value);
             }
             return std::move(obj);
         }
@@ -147,7 +152,7 @@ namespace pyjson
             auto out = wpi::util::json::array();
             for (const py::handle value : obj)
             {
-                out.push_back(to_json(value));
+                out.emplace_back(to_json(value));
             }
             return out;
         }
@@ -173,55 +178,55 @@ namespace pyjson
     }
 }
 
-// nlohmann_json serializers
+// json serializers
 namespace wpi::util
 {
-    #define MAKE_NLJSON_SERIALIZER_DESERIALIZER(T)         \
+    #define MAKE_JSON_SERIALIZER_DESERIALIZER(T)           \
     template <>                                            \
-    struct adl_serializer<T>                               \
+    struct json_serializer<T>                              \
     {                                                      \
-        inline static void to_json(json& j, const T& obj)  \
+        inline static void to(json& j, const T& obj)       \
         {                                                  \
             j = pyjson::to_json(obj);                      \
         }                                                  \
                                                            \
-        inline static T from_json(const json& j)           \
+        inline static T from(const json& j)                \
         {                                                  \
             return pyjson::from_json(j);                   \
         }                                                  \
     }
 
-    #define MAKE_NLJSON_SERIALIZER_ONLY(T)                 \
+    #define MAKE_JSON_SERIALIZER_ONLY(T)                   \
     template <>                                            \
-    struct adl_serializer<T>                               \
+    struct json_serializer<T>                              \
     {                                                      \
-        inline static void to_json(json& j, const T& obj)  \
+        inline static void to(json& j, const T& obj)       \
         {                                                  \
             j = pyjson::to_json(obj);                      \
         }                                                  \
     }
 
-    MAKE_NLJSON_SERIALIZER_DESERIALIZER(py::object);
+    MAKE_JSON_SERIALIZER_DESERIALIZER(py::object);
 
-    MAKE_NLJSON_SERIALIZER_DESERIALIZER(py::bool_);
-    MAKE_NLJSON_SERIALIZER_DESERIALIZER(py::int_);
-    MAKE_NLJSON_SERIALIZER_DESERIALIZER(py::float_);
-    MAKE_NLJSON_SERIALIZER_DESERIALIZER(py::str);
+    MAKE_JSON_SERIALIZER_DESERIALIZER(py::bool_);
+    MAKE_JSON_SERIALIZER_DESERIALIZER(py::int_);
+    MAKE_JSON_SERIALIZER_DESERIALIZER(py::float_);
+    MAKE_JSON_SERIALIZER_DESERIALIZER(py::str);
 
-    MAKE_NLJSON_SERIALIZER_DESERIALIZER(py::list);
-    MAKE_NLJSON_SERIALIZER_DESERIALIZER(py::tuple);
-    MAKE_NLJSON_SERIALIZER_DESERIALIZER(py::dict);
+    MAKE_JSON_SERIALIZER_DESERIALIZER(py::list);
+    MAKE_JSON_SERIALIZER_DESERIALIZER(py::tuple);
+    MAKE_JSON_SERIALIZER_DESERIALIZER(py::dict);
 
-    MAKE_NLJSON_SERIALIZER_ONLY(py::handle);
-    MAKE_NLJSON_SERIALIZER_ONLY(py::detail::item_accessor);
-    MAKE_NLJSON_SERIALIZER_ONLY(py::detail::list_accessor);
-    MAKE_NLJSON_SERIALIZER_ONLY(py::detail::tuple_accessor);
-    MAKE_NLJSON_SERIALIZER_ONLY(py::detail::sequence_accessor);
-    MAKE_NLJSON_SERIALIZER_ONLY(py::detail::str_attr_accessor);
-    MAKE_NLJSON_SERIALIZER_ONLY(py::detail::obj_attr_accessor);
+    MAKE_JSON_SERIALIZER_ONLY(py::handle);
+    MAKE_JSON_SERIALIZER_ONLY(py::detail::item_accessor);
+    MAKE_JSON_SERIALIZER_ONLY(py::detail::list_accessor);
+    MAKE_JSON_SERIALIZER_ONLY(py::detail::tuple_accessor);
+    MAKE_JSON_SERIALIZER_ONLY(py::detail::sequence_accessor);
+    MAKE_JSON_SERIALIZER_ONLY(py::detail::str_attr_accessor);
+    MAKE_JSON_SERIALIZER_ONLY(py::detail::obj_attr_accessor);
 
-    #undef MAKE_NLJSON_SERIALIZER
-    #undef MAKE_NLJSON_SERIALIZER_ONLY
+    #undef MAKE_JSON_SERIALIZER_DESERIALIZER
+    #undef MAKE_JSON_SERIALIZER_ONLY
 }
 
 // pybind11 caster
diff --git a/wpiutil/src/test/native/include/wpi/util/TestPrinters.hpp b/wpiutil/src/test/native/include/wpi/util/TestPrinters.hpp
index eefb5bb9b3..6f3cf95fa0 100644
--- a/wpiutil/src/test/native/include/wpi/util/TestPrinters.hpp
+++ b/wpiutil/src/test/native/include/wpi/util/TestPrinters.hpp
@@ -35,7 +35,7 @@ void PrintTo(std::span<T> val, ::std::ostream* os) {
 }
 
 inline void PrintTo(const json& val, ::std::ostream* os) {
-  *os << val.dump();
+  *os << val.to_string();
 }
 
 }  // namespace wpi::util