YYToolkit is a tool for creating mods and altering GameMaker games.

Currently, only Windows is supported.

YYToolkit Features:

• Intercepting script calls and object events
  • Executing your own code before or after the event
  • Cancelling the event
• Calling any GML function, from any instance
• Plugin support
  • Internal tools can directly call the API using GetProcAddress
    • This allows for more features, like drawing your own overlay with ImGui, or executing your C / C++ function as game code
  • External tools like UndertaleModTool can pull limited information through AUMI's IPC
• Scripting support
  • Dynamically inject GML bytecode or use YYLua!
• Internal UI
  • Can potentially be disabled
  • Plugins can also come with external UIs
• YYC Disassembler
  • And a partial decompiler, too
• Hex Editor
  • Yes, you can mod the data.win without modifying the actual file now!
• String cross-referencer
  • Helpful for finding YYC code entries

Note: GML Compilation is only supported if UndertaleModTool v0.4.0-pre2 or newer is running.