diff --git a/M6502/HarteTest_6502/HarteTest_6502.vcxproj b/M6502/HarteTest_6502/HarteTest_6502.vcxproj
index 29ecc21..80389c8 100644
--- a/M6502/HarteTest_6502/HarteTest_6502.vcxproj
+++ b/M6502/HarteTest_6502/HarteTest_6502.vcxproj
@@ -169,6 +169,7 @@
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="json_t.h" />
+    <ClInclude Include="nlohmann\json.hpp" />
     <ClInclude Include="opcode_test_suite_t.h" />
     <ClInclude Include="state_t.h" />
     <ClInclude Include="stdafx.h" />
diff --git a/M6502/HarteTest_6502/HarteTest_6502.vcxproj.filters b/M6502/HarteTest_6502/HarteTest_6502.vcxproj.filters
index 9cf163c..7fd3cd4 100644
--- a/M6502/HarteTest_6502/HarteTest_6502.vcxproj.filters
+++ b/M6502/HarteTest_6502/HarteTest_6502.vcxproj.filters
@@ -52,5 +52,8 @@
     <ClInclude Include="TestRunner.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="nlohmann\json.hpp">
+      <Filter>Header Files</Filter>
+    </ClInclude>
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/M6502/HarteTest_6502/TestRunner.cpp b/M6502/HarteTest_6502/TestRunner.cpp
index 9fb00db..2d3a006 100644
--- a/M6502/HarteTest_6502/TestRunner.cpp
+++ b/M6502/HarteTest_6502/TestRunner.cpp
@@ -1,7 +1,6 @@
 #include "stdafx.h"
 #include "TestRunner.h"
 
-#include <sstream>
 #include <Disassembly.h>
 
 TestRunner::TestRunner(const test_t& test)
diff --git a/M6502/HarteTest_6502/TestRunner.h b/M6502/HarteTest_6502/TestRunner.h
index ff1c8d7..ee3cdf5 100644
--- a/M6502/HarteTest_6502/TestRunner.h
+++ b/M6502/HarteTest_6502/TestRunner.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <cstdint>
+#include <sstream>
 #include <string>
 #include <vector>
 
diff --git a/M6502/HarteTest_6502/json_t.cpp b/M6502/HarteTest_6502/json_t.cpp
index cf6c135..eb87aba 100644
--- a/M6502/HarteTest_6502/json_t.cpp
+++ b/M6502/HarteTest_6502/json_t.cpp
@@ -1,5 +1,8 @@
 #include "stdafx.h"
 #include "json_t.h"
+
+#ifdef USE_BOOST_JSON
+
 #include <cassert>
 
 const boost::json::value& json_t::get_value(const boost::json::object& object, std::string key) {
@@ -51,3 +54,5 @@ const boost::json::string& json_t::get_string(const boost::json::value& value) {
 const boost::json::string& json_t::get_string(const boost::json::object& object, std::string key) {
     return get_string(get_value(object, key));
 }
+
+#endif
\ No newline at end of file
diff --git a/M6502/HarteTest_6502/json_t.h b/M6502/HarteTest_6502/json_t.h
index b3d158f..1f03a85 100644
--- a/M6502/HarteTest_6502/json_t.h
+++ b/M6502/HarteTest_6502/json_t.h
@@ -1,11 +1,13 @@
 #pragma once
 
-#include <cstdint>
-#include <string>
-
-#include <boost/json.hpp>
+#ifdef USE_BOOST_JSON
+#   include <cstdint>
+#   include <string>
+#   include <boost/json.hpp>
+#endif
 
 class json_t {
+#ifdef USE_BOOST_JSON
 protected:
     [[nodiscard]] static const boost::json::value& get_value(const boost::json::object& object, std::string key);
 
@@ -22,4 +24,5 @@ protected:
 
     [[nodiscard]] static const boost::json::string& get_string(const boost::json::value& value);
     [[nodiscard]] static const boost::json::string& get_string(const boost::json::object& object, std::string key);
+#endif
 };
diff --git a/M6502/HarteTest_6502/opcode_test_suite_t.cpp b/M6502/HarteTest_6502/opcode_test_suite_t.cpp
index b7fb336..db5739e 100644
--- a/M6502/HarteTest_6502/opcode_test_suite_t.cpp
+++ b/M6502/HarteTest_6502/opcode_test_suite_t.cpp
@@ -16,6 +16,8 @@ std::string opcode_test_suite_t::read(std::string path) {
 opcode_test_suite_t::opcode_test_suite_t(std::string path)
 : m_path(path) {}
 
+#ifdef USE_BOOST_JSON
+
 const boost::json::array& opcode_test_suite_t::get_array() const noexcept {
     assert(raw().is_array());
     return raw().get_array();
@@ -25,3 +27,14 @@ void opcode_test_suite_t::load() {
     const auto contents = read(path());
     m_raw = boost::json::parse(contents);
 }
+
+#endif
+
+#ifdef USE_NLOHMANN_JSON
+
+void opcode_test_suite_t::load() {
+    const auto contents = read(path());
+    m_raw = nlohmann::json::parse(contents);
+}
+
+#endif
\ No newline at end of file
diff --git a/M6502/HarteTest_6502/opcode_test_suite_t.h b/M6502/HarteTest_6502/opcode_test_suite_t.h
index aabac89..63dbafb 100644
--- a/M6502/HarteTest_6502/opcode_test_suite_t.h
+++ b/M6502/HarteTest_6502/opcode_test_suite_t.h
@@ -1,21 +1,36 @@
 #pragma once
 
 #include <string>
-#include <boost/json.hpp>
+
+#ifdef USE_BOOST_JSON
+#	include <boost/json.hpp>
+#endif
+
+#ifdef USE_NLOHMANN_JSON
+#   include "nlohmann/json.hpp"
+#endif
 
 class opcode_test_suite_t final {
 private:
     [[nodiscard]] static std::string read(std::string path);
 
     std::string m_path;
+#ifdef USE_BOOST_JSON
     boost::json::value m_raw;
+#endif
+#ifdef USE_NLOHMANN_JSON
+    nlohmann::json m_raw;
+#endif
 
 public:
     opcode_test_suite_t(std::string path);
 
     [[nodiscard]] constexpr const auto& path() const noexcept { return m_path; }
     [[nodiscard]] constexpr const auto& raw() const noexcept { return m_raw; }
+
+#ifdef USE_BOOST_JSON
     [[nodiscard]] const boost::json::array& get_array() const noexcept;
+#endif
 
     void load();
 };
diff --git a/M6502/HarteTest_6502/state_t.cpp b/M6502/HarteTest_6502/state_t.cpp
index 70e538b..99adee9 100644
--- a/M6502/HarteTest_6502/state_t.cpp
+++ b/M6502/HarteTest_6502/state_t.cpp
@@ -2,6 +2,21 @@
 #include "state_t.h"
 #include <cassert>
 
+state_t::state_t() {}
+
+#ifdef USE_BOOST_JSON
+
+state_t::state_t(const boost::json::object& serialised) {
+    initialise(serialised);
+    assert(initialised());
+}
+
+state_t::state_t(const boost::json::value& serialised) {
+    assert(serialised.is_object());
+    initialise(serialised.get_object());
+    assert(initialised());
+}
+
 void state_t::initialise(const boost::json::object& serialised) {
 
     assert(!initialised());
@@ -26,15 +41,38 @@ void state_t::initialise(const boost::json::object& serialised) {
     m_initialised = true;
 }
 
-state_t::state_t() {}
+#endif
 
-state_t::state_t(const boost::json::object& serialised) {
+#ifdef USE_NLOHMANN_JSON
+
+state_t::state_t(const nlohmann::json& serialised) {
+    assert(serialised.is_object());
     initialise(serialised);
     assert(initialised());
 }
 
-state_t::state_t(const boost::json::value& serialised) {
-    assert(serialised.is_object());
-    initialise(serialised.get_object());
-    assert(initialised());
+void state_t::initialise(const nlohmann::json& serialised) {
+
+    assert(!initialised());
+
+    m_pc = serialised["pc"].get<uint16_t>();
+    m_s = serialised["s"].get<uint8_t>();
+    m_a = serialised["a"].get<uint8_t>();
+    m_x = serialised["x"].get<uint8_t>();
+    m_y = serialised["y"].get<uint8_t>();
+    m_p = serialised["p"].get<uint8_t>();
+
+    const auto& ram_entries = serialised["ram"];
+    assert(ram_entries.is_array());
+    for (const auto& ram_entry : ram_entries) {
+        assert(ram_entry.is_array());
+        assert(ram_entry.size() == 2);
+        const auto address = ram_entry[0].get<uint16_t>();
+        const auto value = ram_entry[1].get<uint8_t>();
+        m_ram[address] = value;
+    }
+
+    m_initialised = true;
 }
+
+#endif
diff --git a/M6502/HarteTest_6502/state_t.h b/M6502/HarteTest_6502/state_t.h
index be2d8f2..70bc2d1 100644
--- a/M6502/HarteTest_6502/state_t.h
+++ b/M6502/HarteTest_6502/state_t.h
@@ -2,7 +2,14 @@
 
 #include <cstdint>
 #include <unordered_map>
-#include <boost/json.hpp>
+
+#ifdef USE_BOOST_JSON
+#	include <boost/json.hpp>
+#endif
+
+#ifdef USE_NLOHMANN_JSON
+#   include "nlohmann/json.hpp"
+#endif
 
 #include "json_t.h"
 
@@ -20,12 +27,25 @@ private:
 
     [[nodiscard]] constexpr auto initialised() const noexcept { return m_initialised; }
 
+#ifdef USE_BOOST_JSON
     void initialise(const boost::json::object& serialised);
+#endif
+
+#ifdef USE_NLOHMANN_JSON
+    void initialise(const nlohmann::json& serialised);
+#endif
 
 public:
     state_t();
+
+#ifdef USE_BOOST_JSON
     state_t(const boost::json::object& serialised);
     state_t(const boost::json::value& serialised);
+#endif
+
+#ifdef USE_NLOHMANN_JSON
+    state_t(const nlohmann::json& serialised);
+#endif
 
     [[nodiscard]] constexpr auto pc() const noexcept { return m_pc; }
     [[nodiscard]] constexpr auto s() const noexcept { return m_s; }
diff --git a/M6502/HarteTest_6502/stdafx.h b/M6502/HarteTest_6502/stdafx.h
index 4cfb9a1..6edae2f 100644
--- a/M6502/HarteTest_6502/stdafx.h
+++ b/M6502/HarteTest_6502/stdafx.h
@@ -11,4 +11,13 @@
 #include <unordered_map>
 #include <vector>
 
-#include <boost/json.hpp>
+//#define USE_BOOST_JSON
+#define USE_NLOHMANN_JSON
+
+#ifdef USE_BOOST_JSON
+#	include <boost/json.hpp>
+#endif
+
+#ifdef USE_NLOHMANN_JSON
+#	include "nlohmann/json.hpp"
+#endif
\ No newline at end of file
diff --git a/M6502/HarteTest_6502/test_t.cpp b/M6502/HarteTest_6502/test_t.cpp
index 5816f3a..51c2bff 100644
--- a/M6502/HarteTest_6502/test_t.cpp
+++ b/M6502/HarteTest_6502/test_t.cpp
@@ -19,6 +19,17 @@ std::string test_t::to_string(action value) {
     throw new std::out_of_range("Unknown action");
 }
 
+#ifdef USE_BOOST_JSON
+
+test_t::test_t(const boost::json::object& serialised) {
+    initialise(serialised);
+}
+
+test_t::test_t(const boost::json::value& serialised) {
+    assert(serialised.is_object());
+    initialise(serialised.get_object());
+}
+
 void test_t::initialise(const boost::json::object& serialised) {
 
     m_name = get_string(serialised, "name");
@@ -34,15 +45,35 @@ void test_t::initialise(const boost::json::object& serialised) {
         const auto address = get_uint16(cycle_array[0]);
         const auto contents = get_uint8(cycle_array[1]);
         const auto action = to_action((std::string)get_string(cycle_array[2]));
-        m_cycles.push_back( { address, contents, action } );
+        m_cycles.push_back({ address, contents, action });
     }
 }
 
-test_t::test_t(const boost::json::object& serialised) {
+#endif
+
+#ifdef USE_NLOHMANN_JSON
+
+test_t::test_t(const nlohmann::json& serialised) {
+    assert(serialised.is_object());
     initialise(serialised);
 }
 
-test_t::test_t(const boost::json::value& serialised) {
-    assert(serialised.is_object());
-    initialise(serialised.get_object());
+void test_t::initialise(const nlohmann::json& serialised) {
+
+    m_name = serialised["name"].get<std::string>();
+    m_initial_state = state_t(serialised["initial"]);
+    m_final_state = state_t(serialised["final"]);
+
+    const auto& cycles_array = serialised["cycles"];
+    m_cycles.reserve(cycles_array.size());
+
+    for (const auto& cycles_entry : cycles_array) {
+        assert(cycles_entry.size() == 3);
+        const auto address = cycles_entry[0].get<uint16_t>();
+        const auto contents = cycles_entry[1].get<uint8_t>();
+        const auto action = to_action(cycles_entry[2].get<std::string>());
+        m_cycles.push_back({ address, contents, action });
+    }
 }
+
+#endif
diff --git a/M6502/HarteTest_6502/test_t.h b/M6502/HarteTest_6502/test_t.h
index fafd366..8d0e4e6 100644
--- a/M6502/HarteTest_6502/test_t.h
+++ b/M6502/HarteTest_6502/test_t.h
@@ -4,7 +4,14 @@
 #include <string>
 #include <vector>
 #include <tuple>
-#include <boost/json.hpp>
+
+#ifdef USE_BOOST_JSON
+#	include <boost/json.hpp>
+#endif
+
+#ifdef USE_NLOHMANN_JSON
+#   include "nlohmann/json.hpp"
+#endif
 
 #include "state_t.h"
 #include "json_t.h"
@@ -25,11 +32,24 @@ private:
     state_t m_final_state;
     events_t m_cycles; 
 
+#ifdef USE_BOOST_JSON
     void initialise(const boost::json::object& serialised);
+#endif
+
+#ifdef USE_NLOHMANN_JSON
+    void initialise(const nlohmann::json& serialised);
+#endif
 
 public:
+
+#ifdef USE_BOOST_JSON
     test_t(const boost::json::object& serialised);
     test_t(const boost::json::value& serialised);
+#endif
+
+#ifdef USE_NLOHMANN_JSON
+    test_t(const nlohmann::json& serialised);
+#endif
 
     [[nodiscard]] constexpr const auto& name() const noexcept { return m_name; }
     [[nodiscard]] constexpr const auto& initial_state() const noexcept { return m_initial_state; }
diff --git a/M6502/HarteTest_6502/tests.cpp b/M6502/HarteTest_6502/tests.cpp
index 7de0e6a..7ecae50 100644
--- a/M6502/HarteTest_6502/tests.cpp
+++ b/M6502/HarteTest_6502/tests.cpp
@@ -1,5 +1,6 @@
 #include "stdafx.h"
 
+#include <chrono>
 #include <iostream>
 #include <filesystem>
 
@@ -11,6 +12,8 @@ int main() {
 
 	std::filesystem::path location = "C:\\github\\spectrum\\libraries\\EightBit\\modules\\ProcessorTests\\6502\\v1";
 
+    const auto start_time = std::chrono::steady_clock::now();
+
     for (const auto& entry : std::filesystem::directory_iterator{ location }) {
 
         const auto path = entry.path();
@@ -20,7 +23,13 @@ int main() {
 
         opcode_test_suite_t opcode(path.string());
         opcode.load();
+
+#ifdef USE_BOOST_JSON
         const auto& opcode_test_array = opcode.get_array();
+#endif
+#ifdef USE_NLOHMANN_JSON
+        const auto& opcode_test_array = opcode.raw();
+#endif
 
         bool opcode_bad = false;
         for (const auto& opcode_test_element : opcode_test_array) {
@@ -39,4 +48,12 @@ int main() {
             }
         }
     }
+
+    const auto finish_time = std::chrono::steady_clock::now();
+
+    const auto elapsed_time = finish_time - start_time;
+
+    const auto seconds = std::chrono::duration_cast<std::chrono::duration<double>>(elapsed_time).count();
+
+    std::cout << "Elapsed time: " << seconds << " seconds" << std::endl;
 }
\ No newline at end of file