YYToolkit

YYToolkit is a tool for creating mods and altering GameMaker games, supported on Windows 8.1 → Windows 11.

Features

Plugin Support
- Run custom code in the game's context via a robust callback system
- Detour game functions to your plugin to implement custom functionality
Well-documented
- The wiki has most API functions documented for both YYTK Legacy and YYTK Next
Full access to GameMaker functions, scripts, and variables
Full compatibility with existing tools like UndertaleModTool or Dogscepter
Runtime loading / unloading
- Mods can be managed seamlessly while the game is running

Getting help

Help with YYToolkit or Aurie Framework - Arch Wizards Server
General game modding questions - Underminers Server

YYTK Editions

YYTK is split on two branches, that being Legacy and Stable (Next).

Note

❌ = Unsupported 🟠 = Limited support 🟡 = Supported, unreliable ✅ = Supported

Point of comparison	YYToolkit Legacy	YYToolkit Next
GM 1.4.x	🟡	❌
GM 2.x.x	✅	🟠
GM 2022.x	🟠	✅
GM 2023.x	❌	✅
GM 2024.x beta	❌	✅
VM runner support	✅	🟡
x86 runner support	✅	🟡
x64 runner support	🟡	✅
Active Development	❌	✅
Accessing global variables	✅	✅
Accessing local variables	🟠	✅
Accessing built-in variables	❌	✅
Accessing data structures	❌	✅
Accessing scripts	🟡	✅
Accessing rooms	❌	✅
Manipulating object events	❌	🟠

Contributors

YYTK Next
- mashirochan for the awesome work on streamlining the installation process
- PippleCultist for reporting bugs
- ramennnoodle for creating how-to guides on getting YYToolkit and Aurie running on Linux
YYTK Legacy
- MousieDev for creating makefiles (which probably don't work at this point)
- Miepee for the awesome icon!
- TheEternalShine for testing and giving feedback on in-development versions of the tool.

Donations

YYToolkit is, and likely always will be, free software.