diff --git a/.gitmodules b/.gitmodules
index f89fde895..dec6600f3 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,6 +1,3 @@
-[submodule "tests/third_party/json"]
-	path = tests/third_party/json
-	url = https://github.com/aseprite/json.lua
 [submodule "third_party/pixman"]
 	path = third_party/pixman
 	url = https://github.com/aseprite/pixman.git
diff --git a/src/app/CMakeLists.txt b/src/app/CMakeLists.txt
index b7ab12109..b5bac13f8 100644
--- a/src/app/CMakeLists.txt
+++ b/src/app/CMakeLists.txt
@@ -184,6 +184,7 @@ if(ENABLE_SCRIPTING)
     script/image_iterator_class.cpp
     script/image_spec_class.cpp
     script/images_class.cpp
+    script/json_class.cpp
     script/keys.cpp
     script/layer_class.cpp
     script/layers_class.cpp
diff --git a/src/app/script/engine.cpp b/src/app/script/engine.cpp
index 1150ba175..576fb8d2c 100644
--- a/src/app/script/engine.cpp
+++ b/src/app/script/engine.cpp
@@ -154,6 +154,7 @@ void register_app_pixel_color_object(lua_State* L);
 void register_app_fs_object(lua_State* L);
 void register_app_command_object(lua_State* L);
 void register_app_preferences_object(lua_State* L);
+void register_json_object(lua_State* L);
 
 void register_brush_class(lua_State* L);
 void register_cel_class(lua_State* L);
@@ -255,12 +256,13 @@ Engine::Engine()
   // Generic code used by metatables
   run_mt_index_code(L);
 
-  // Register global app object
+  // Register global objects (app, json)
   register_app_object(L);
   register_app_pixel_color_object(L);
   register_app_fs_object(L);
   register_app_command_object(L);
   register_app_preferences_object(L);
+  register_json_object(L);
 
   // Register constants
   lua_newtable(L);
diff --git a/src/app/script/json_class.cpp b/src/app/script/json_class.cpp
new file mode 100644
index 000000000..f13f0fe93
--- /dev/null
+++ b/src/app/script/json_class.cpp
@@ -0,0 +1,314 @@
+// Aseprite
+// Copyright (C) 2023  Igara Studio S.A.
+//
+// This program is distributed under the terms of
+// the End-User License Agreement for Aseprite.
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "app/script/luacpp.h"
+#include "app/script/values.h"
+
+#include <cstring>
+
+#include "json11.hpp"
+
+namespace app {
+namespace script {
+
+namespace {
+
+struct Json { };
+using JsonObj = json11::Json;
+using JsonArrayIterator = JsonObj::array::const_iterator;
+using JsonObjectIterator = JsonObj::object::const_iterator;
+
+void push_json_value(lua_State* L, const JsonObj& value)
+{
+  switch (value.type()) {
+    case json11::Json::NUL:
+      lua_pushnil(L);
+      break;
+    case json11::Json::NUMBER:
+      lua_pushnumber(L, value.number_value());
+      break;
+    case json11::Json::BOOL:
+      lua_pushboolean(L, value.bool_value());
+      break;
+    case json11::Json::STRING:
+      lua_pushstring(L, value.string_value().c_str());
+      break;
+    case json11::Json::ARRAY:
+    case json11::Json::OBJECT:
+      push_obj(L, value);
+      break;
+  }
+}
+
+JsonObj get_json_value(lua_State* L, int index)
+{
+  switch (lua_type(L, index)) {
+
+    case LUA_TNONE:
+    case LUA_TNIL:
+      return JsonObj();
+
+    case LUA_TBOOLEAN:
+      return JsonObj(lua_toboolean(L, index) ? true: false);
+
+    case LUA_TNUMBER:
+      return JsonObj(lua_tonumber(L, index));
+
+    case LUA_TSTRING:
+      return JsonObj(lua_tostring(L, index));
+
+    case LUA_TTABLE:
+      if (is_array_table(L, index)) {
+        JsonObj::array items;
+        if (index < 0)
+          --index;
+        lua_pushnil(L);
+        while (lua_next(L, index) != 0) {
+          items.push_back(get_json_value(L, -1));
+          lua_pop(L, 1);          // pop the value lua_next(), leave the key in the stack
+        }
+        return JsonObj(items);
+      }
+      else {
+        JsonObj::object items;
+        lua_pushnil(L);
+        if (index < 0)
+          --index;
+        while (lua_next(L, index) != 0) {
+          if (const char* k = lua_tostring(L, -2)) {
+            items[k] = get_json_value(L, -1);
+          }
+          lua_pop(L, 1);          // pop the value lua_next(), leave the key in the stack
+        }
+        return JsonObj(items);
+      }
+      break;
+
+    case LUA_TUSERDATA:
+      // TODO convert rectangles, point, size, uuids?
+      break;
+
+  }
+  return JsonObj();
+}
+
+int JsonObj_gc(lua_State* L)
+{
+  get_obj<JsonObj>(L, 1)->~JsonObj();
+  return 0;
+}
+
+int JsonObj_eq(lua_State* L)
+{
+  auto a = get_obj<JsonObj>(L, 1);
+  auto b = get_obj<JsonObj>(L, 2);
+  return (*a == *b);
+}
+
+int JsonObj_len(lua_State* L)
+{
+  auto obj = get_obj<JsonObj>(L, 1);
+  switch (obj->type()) {
+    case json11::Json::STRING:
+      lua_pushinteger(L, obj->string_value().size());
+      break;
+    case json11::Json::ARRAY:
+      lua_pushinteger(L, obj->array_items().size());
+      break;
+    case json11::Json::OBJECT:
+      lua_pushinteger(L, obj->object_items().size());
+      break;
+    case json11::Json::NUL:
+      lua_pushnil(L);
+      break;
+    default:
+    case json11::Json::NUMBER:
+    case json11::Json::BOOL:
+      lua_pushinteger(L, 1);
+      break;
+  }
+  return 1;
+}
+
+int JsonObj_index(lua_State* L)
+{
+  auto obj = get_obj<JsonObj>(L, 1);
+  if (obj->type() == json11::Json::OBJECT) {
+    if (auto key = lua_tostring(L, 2)) {
+      push_json_value(L, (*obj)[key]);
+      return 1;
+    }
+  }
+  else if (obj->type() == json11::Json::ARRAY) {
+    auto i = lua_tointeger(L, 2) - 1; // Adjust to 0-based index
+    push_json_value(L, (*obj)[i]);
+    return 1;
+  }
+  return 0;
+}
+
+int JsonObj_newindex(lua_State* L)
+{
+  auto obj = get_obj<JsonObj>(L, 1);
+  if (obj->type() == json11::Json::OBJECT) {
+    if (auto key = lua_tostring(L, 2)) {
+      // TODO ugly hack, but it works
+      const_cast<std::map<std::string, json11::Json>&>
+        (obj->object_items())[key] = get_json_value(L, 3);
+    }
+  }
+  else if (obj->type() == json11::Json::ARRAY) {
+    auto i = lua_tointeger(L, 2) - 1; // Adjust to 0-based index
+    const_cast<std::vector<json11::Json>&>
+      (obj->array_items())[i] = get_json_value(L, 3);
+  }
+  return 0;
+}
+
+int JsonObj_pairs_next(lua_State* L)
+{
+  auto obj = get_obj<JsonObj>(L, 1);
+  auto& it = *get_obj<JsonObjectIterator>(L, lua_upvalueindex(1));
+  if (it == obj->object_items().end())
+    return 0;
+  lua_pushstring(L, (*it).first.c_str());
+  push_json_value(L, (*it).second);
+  ++it;
+  return 2;
+}
+
+int JsonObj_ipairs_next(lua_State* L)
+{
+  auto obj = get_obj<JsonObj>(L, 1);
+  auto& it = *get_obj<JsonArrayIterator>(L, lua_upvalueindex(1));
+  if (it == obj->array_items().end())
+    return 0;
+  lua_pushinteger(L, (it - obj->array_items().begin() + 1));
+  push_json_value(L, (*it));
+  ++it;
+  return 0;
+}
+
+int JsonObj_pairs(lua_State* L)
+{
+  auto obj = get_obj<JsonObj>(L, 1);
+  if (obj->type() == json11::Json::OBJECT) {
+    push_obj(L, obj->object_items().begin());
+    lua_pushcclosure(L, JsonObj_pairs_next, 1);
+    lua_pushvalue(L, 1); // Copy the same obj as the second return value
+    return 2;
+  }
+  else if (obj->type() == json11::Json::ARRAY) {
+    push_obj(L, obj->array_items().begin());
+    lua_pushcclosure(L, JsonObj_ipairs_next, 1);
+    lua_pushvalue(L, 1); // Copy the same obj as the second return value
+    return 2;
+  }
+  return 0;
+}
+
+int JsonObj_tostring(lua_State* L)
+{
+  auto obj = get_obj<JsonObj>(L, 1);
+  lua_pushstring(L, obj->dump().c_str());
+  return 1;
+}
+
+int JsonObjectIterator_gc(lua_State* L)
+{
+  get_obj<JsonObjectIterator>(L, 1)->~JsonObjectIterator();
+  return 0;
+}
+
+int JsonArrayIterator_gc(lua_State* L)
+{
+  get_obj<JsonArrayIterator>(L, 1)->~JsonArrayIterator();
+  return 0;
+}
+
+int Json_decode(lua_State* L)
+{
+  if (const char* s = lua_tostring(L, 1)) {
+    std::string err;
+    auto json = json11::Json::parse(s, std::strlen(s), err);
+    if (!err.empty())
+      return luaL_error(L, err.c_str());
+    push_obj(L, json);
+    return 1;
+  }
+  return 0;
+}
+
+int Json_encode(lua_State* L)
+{
+  // Encode a JsonObj, we deep copy it (create a deep copy)
+  if (auto obj = may_get_obj<JsonObj>(L, 1)) {
+    lua_pushstring(L, obj->dump().c_str());
+    return 1;
+  }
+  // Encode a Lua table
+  else if (lua_istable(L, 1)) {
+    lua_pushstring(L, get_json_value(L, 1).dump().c_str());
+    return 1;
+  }
+  return 0;
+}
+
+const luaL_Reg JsonObj_methods[] = {
+  { "__gc",       JsonObj_gc },
+  { "__eq",       JsonObj_eq },
+  { "__len",      JsonObj_len },
+  { "__index",    JsonObj_index },
+  { "__newindex", JsonObj_newindex },
+  { "__pairs",    JsonObj_pairs },
+  { "__tostring", JsonObj_tostring },
+  { nullptr,      nullptr }
+};
+
+const luaL_Reg JsonObjectIterator_methods[] = {
+  { "__gc",       JsonObjectIterator_gc },
+  { nullptr,      nullptr }
+};
+
+const luaL_Reg JsonArrayIterator_methods[] = {
+  { "__gc",       JsonArrayIterator_gc },
+  { nullptr,      nullptr }
+};
+
+const luaL_Reg Json_methods[] = {
+  { "decode",     Json_decode },
+  { "encode",     Json_encode },
+  { nullptr,      nullptr }
+};
+
+} // anonymous namespace
+
+DEF_MTNAME(Json);
+DEF_MTNAME(JsonObj);
+DEF_MTNAME(JsonObjectIterator);
+DEF_MTNAME(JsonArrayIterator);
+
+void register_json_object(lua_State* L)
+{
+  REG_CLASS(L, JsonObj);
+  REG_CLASS(L, JsonObjectIterator);
+  REG_CLASS(L, JsonArrayIterator);
+  REG_CLASS(L, Json);
+
+  lua_newtable(L);              // Create a table which will be the "json" object
+  lua_pushvalue(L, -1);
+  luaL_getmetatable(L, get_mtname<Json>());
+  lua_setmetatable(L, -2);
+  lua_setglobal(L, "json");
+  lua_pop(L, 1);                // Pop json table
+}
+
+} // namespace script
+} // namespace app
diff --git a/src/app/script/values.cpp b/src/app/script/values.cpp
index 7f4478094..dcd2176d2 100644
--- a/src/app/script/values.cpp
+++ b/src/app/script/values.cpp
@@ -467,37 +467,14 @@ doc::UserData::Variant get_value_from_lua(lua_State* L, int index)
       v = std::string(lua_tostring(L, index));
       break;
 
-    case LUA_TTABLE: {
-      int i = 0;
-      bool isArray = true;
-      if (index < 0)
-        --index;
-      lua_pushnil(L);
-      while (lua_next(L, index) != 0) {
-        if (lua_isinteger(L, -2)) {
-          if (++i != lua_tointeger(L, -2)) {
-            isArray = false;
-            lua_pop(L, 2);  // Pop value and key
-            break;
-          }
-        }
-        else {
-          isArray = false;
-          lua_pop(L, 2);
-          break;
-        }
-        lua_pop(L, 1); // Pop the value, leave the key for lua_next()
-      }
-      if (index < 0)
-        ++index;
-      if (isArray) {
+    case LUA_TTABLE:
+      if (is_array_table(L, index)) {
         v = get_value_from_lua<doc::UserData::Vector>(L, index);
       }
       else {
         v = get_value_from_lua<doc::UserData::Properties>(L, index);
       }
       break;
-    }
 
     case LUA_TUSERDATA: {
       if (auto rect = may_get_obj<gfx::Rect>(L, index)) {
@@ -579,5 +556,28 @@ doc::UserData::Vector get_value_from_lua(lua_State* L, int index)
   return v;
 }
 
+bool is_array_table(lua_State* L, int index)
+{
+  if (index < 0)
+    --index;
+
+  int i = 0;
+  lua_pushnil(L);
+  while (lua_next(L, index) != 0) {
+    if (lua_isinteger(L, -2)) {
+      if (++i != lua_tointeger(L, -2)) {
+        lua_pop(L, 2);  // Pop value and key
+        return false;
+      }
+    }
+    else {
+      lua_pop(L, 2);
+      return false;
+    }
+    lua_pop(L, 1); // Pop the value, leave the key for lua_next()
+  }
+  return true;
+}
+
 } // namespace script
 } // namespace app
diff --git a/src/app/script/values.h b/src/app/script/values.h
index 7b5044a18..400267d0b 100644
--- a/src/app/script/values.h
+++ b/src/app/script/values.h
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2019  Igara Studio S.A.
+// Copyright (C) 2019-2023  Igara Studio S.A.
 //
 // This program is distributed under the terms of
 // the End-User License Agreement for Aseprite.
@@ -21,6 +21,9 @@ T get_value_from_lua(lua_State* L, int index);
 template<typename T>
 void push_value_to_lua(lua_State* L, const T& value);
 
+// Returns true if the given table is an array
+bool is_array_table(lua_State* L, int index);
+
 } // namespace script
 } // namespace app
 
diff --git a/tests/cli/sheet.sh b/tests/cli/sheet.sh
index d0e2dad81..7bcd294e2 100644
--- a/tests/cli/sheet.sh
+++ b/tests/cli/sheet.sh
@@ -17,7 +17,6 @@ if ! $ASEPRITE -b sprites/1empty3.aseprite --sheet "$d/sheet.png" > "$d/stdout.j
    exit 1
 fi
 cat >$d/compare.lua <<EOF
-local json = dofile('third_party/json/json.lua')
 local data = json.decode(io.open('$d/stdout.json'):read('a'))
 local frames = { data.frames['1empty3 0.aseprite'],
                  data.frames['1empty3 1.aseprite'],
@@ -93,7 +92,6 @@ $ASEPRITE -b --split-layers sprites/1empty3.aseprite \
 	  --sheet "$d/sheet.png" \
 	  --data "$d/sheet.json" || exit 1
 cat >$d/compare.lua <<EOF
-local json = dofile('third_party/json/json.lua')
 local data = json.decode(io.open('$d/sheet.json'):read('a'))
 assert(data.meta.size.w == 96)
 assert(data.meta.size.h == 64)
@@ -159,7 +157,6 @@ $ASEPRITE -b \
 	  -data "$d/sheet2.json" || exit 1
 
 cat >$d/check.lua <<EOF
-local json = dofile('third_party/json/json.lua')
 local sheet1 = json.decode(io.open('$d/sheet1.json'):read('a'))
 local sheet2 = json.decode(io.open('$d/sheet2.json'):read('a'))
 assert(#sheet1.frames == 12)
@@ -258,7 +255,6 @@ for layer in a b ; do
 	      -data "$d/data2-$layer.json" \
 	      -format json-array -sheet "$d/sheet2-$layer.png" || exit 1
     cat >$d/compare.lua <<EOF
-local json = dofile('third_party/json/json.lua')
 local data1 = json.decode(io.open('$d/data1-$layer.json'):read('a'))
 local data2 = json.decode(io.open('$d/data2-$layer.json'):read('a'))
 assert(#data1.frames == #data2.frames)
@@ -289,7 +285,6 @@ $ASEPRITE -b \
 	  -data "$d/data2.json" \
 	  -format json-array -sheet-pack -sheet "$d/sheet2.png" || exit 1
 cat >$d/compare.lua <<EOF
-local json = dofile('third_party/json/json.lua')
 local data1 = json.decode(io.open('$d/data1.json'):read('a'))
 local data2 = json.decode(io.open('$d/data2.json'):read('a'))
 assert(#data1.frames == #data2.frames)
@@ -308,7 +303,6 @@ d=$t/issue-2380
 $ASEPRITE -b -trim -all-layers "sprites/groups3abc.aseprite" -data "$d/sheet1.json" -format json-array -sheet "$d/sheet1.png" -list-layers
 $ASEPRITE -b -trim -all-layers -split-layers "sprites/groups3abc.aseprite" -data "$d/sheet2.json" -format json-array -sheet "$d/sheet2.png" -list-layers
 cat >$d/check.lua <<EOF
-local json = dofile('third_party/json/json.lua')
 local sheet1 = json.decode(io.open('$d/sheet1.json'):read('a'))
 local sheet2 = json.decode(io.open('$d/sheet2.json'):read('a'))
 assert(#sheet1.meta.layers == 12)
@@ -323,7 +317,6 @@ d=$t/issue-2432
 $ASEPRITE -b -trim -ignore-layer "c" -all-layers "sprites/groups3abc.aseprite" -data "$d/sheet1.json" -format json-array -sheet "$d/sheet1.png" -list-layers
 $ASEPRITE -b -trim -ignore-layer "c" -all-layers -split-layers "sprites/groups3abc.aseprite" -data "$d/sheet2.json" -format json-array -sheet "$d/sheet2.png" -list-layers
 cat >$d/check.lua <<EOF
-local json = dofile('third_party/json/json.lua')
 local sheet1 = json.decode(io.open('$d/sheet1.json'):read('a'))
 local sheet2 = json.decode(io.open('$d/sheet2.json'):read('a'))
 assert(#sheet1.meta.layers == 8)
@@ -337,7 +330,6 @@ $ASEPRITE -b -script "$d/check.lua" || exit 1
 d=$t/issue-2600
 $ASEPRITE -b -list-layers -format json-array -trim -merge-duplicates -split-layers -all-layers "sprites/link.aseprite" -data "$d/sheet.json" -sheet "$d/sheet.png"
 cat >$d/check.lua <<EOF
-local json = dofile('third_party/json/json.lua')
 local sheet = json.decode(io.open('$d/sheet.json'):read('a'))
 local restoredSprite = Sprite(sheet.frames[1].sourceSize.w, sheet.frames[1].sourceSize.h, ColorMode.RGB)
 local spriteSheet = Image{ fromFile="$d/sheet.png" }
@@ -409,7 +401,6 @@ $ASEPRITE -b "sprites/1empty3.aseprite" "sprites/tags3.aseprite" \
 	  -sheet "$d/atlas.png" \
 	  -list-tags -tagname-format="{title}-{tag}" || exit 1
 cat >$d/compare.lua <<EOF
-local json = dofile('third_party/json/json.lua')
 local data = json.decode(io.open('$d/atlas.json'):read('a'))
 assert(#data.meta.frameTags == 5)
 
diff --git a/tests/scripts/compare_sprite_sheets.lua b/tests/scripts/compare_sprite_sheets.lua
index 713c43899..e9605e767 100644
--- a/tests/scripts/compare_sprite_sheets.lua
+++ b/tests/scripts/compare_sprite_sheets.lua
@@ -9,7 +9,6 @@ if file1 == nil or file2 == nil then
   return 0
 end
 
-local json = dofile('../third_party/json/json.lua')
 local data1 = json.decode(io.open(file1):read('a'))
 local data2 = json.decode(io.open(file2):read('a'))
 
diff --git a/tests/scripts/json.lua b/tests/scripts/json.lua
new file mode 100644
index 000000000..b7f6d6063
--- /dev/null
+++ b/tests/scripts/json.lua
@@ -0,0 +1,73 @@
+-- Copyright (C) 2023  Igara Studio S.A.
+--
+-- This file is released under the terms of the MIT license.
+-- Read LICENSE.txt for more information.
+
+-- Basic decode + iterators
+do
+  local o = json.decode('{"a":true,"b":5,"c":[1,3,9]}')
+  assert(#o == 3)
+  assert(o.a == true)
+  assert(o.b == 5)
+  assert(#o.c == 3)
+  assert(o.c[1] == 1)
+  assert(o.c[2] == 3)
+  assert(o.c[3] == 9)
+
+  -- Iterate json data
+  for k,v in pairs(o) do
+    if k == "a" then assert(v == true) end
+    if k == "b" then assert(v == 5) end
+    if k == "c" then
+      assert(v[1] == 1)
+      assert(v[2] == 3)
+      assert(v[3] == 9)
+    end
+  end
+
+  for i,v in ipairs(o.c) do
+    if i == 1 then assert(v == 1) end
+    if i == 2 then assert(v == 3) end
+    if i == 3 then assert(v == 9) end
+  end
+end
+
+-- Modify values
+do
+  local o = json.decode('{"obj":{"a":3,"b":5},"arr":[0,"hi",{"bye":true}]}')
+  assert(o.obj.a == 3)
+  assert(o.obj.b == 5)
+  assert(o.arr[1] == 0)
+  assert(o.arr[2] == "hi")
+  assert(o.arr[3].bye == true)
+
+  local u = json.decode(json.encode(o)) -- Creates a copy
+  assert(o == o)
+  assert(o == u)
+
+  o.obj.b = 6
+  o.arr[1] = "name"
+  assert(tostring(o.obj) == '{"a": 3, "b": 6}')
+  assert(tostring(o.arr) == '["name", "hi", {"bye": true}]')
+  -- Check that "u" is a copy and wasn't modify (only "o" was modified)
+  assert(tostring(u.obj) == '{"a": 3, "b": 5}')
+  assert(tostring(u.arr) == '[0, "hi", {"bye": true}]')
+end
+
+-- Encode Lua tables
+do
+  local arrStr = json.encode({ 4, "hi", true })
+  assert(arrStr == '[4, "hi", true]')
+  local arr = json.decode(arrStr)
+  assert(arr[1] == 4)
+  assert(arr[2] == "hi")
+  assert(arr[3] == true)
+
+  local obj = json.decode(json.encode({ a=4, b=true, c="name", d={1,8,{a=2}} }))
+  assert(obj.a == 4)
+  assert(obj.b == true)
+  assert(obj.c == "name")
+  assert(obj.d[1] == 1)
+  assert(obj.d[2] == 8)
+  assert(obj.d[3].a == 2)
+end
diff --git a/tests/third_party/json b/tests/third_party/json
deleted file mode 160000
index dbf4b2dd2..000000000
--- a/tests/third_party/json
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit dbf4b2dd2eb7c23be2773c89eb059dadd6436f94