As of 2026, the most reliable, actively maintained, and free tool for inspecting and modifying GameMaker games—specifically those built with GM:S 1.4 or GMS2—is , created by the community-driven "UnderminersTeam." Why UndertaleModTool?
is used to generate native machine code. Decompilers attempt to read this bytecode and reconstruct the original GameMaker Language (GML). Limitations:
(open source, free)
True "decompilation"—reverting a game to a fully functional .yyp project—is not natively supported by GameMaker. However, you can use these tools to recover specific parts of a lost project: game maker studio 2 decompiler free install
GMS2 games can be compiled in two main ways:
: Navigate to the Releases section and download the latest GUI version (e.g., UndertaleModTool_v0.x.x.x-Windows.zip ).
Once installed, using a tool like UTMT follows a general pattern. This process is not intended to be a step-by-step guide but an illustration of how these tools are used in practice. As of 2026, the most reliable, actively maintained,
In this write-up, we'll explore the concept of decompiling Game Maker Studio 2 projects and provide a step-by-step guide on how to install a free decompiler.
: It works best with games that use a data.win file (Windows) or game.ios / game.unx (Mac/Linux). Installation & Basic Usage Guide
Use the built-in scripts menu (e.g., Scripts > ResourceUnpacker ) to automatically dump all sprites, audio files, and decompiled GML code into an organized folder structure. Security Risks: Beware of "Free Premium Installers" This process is not intended to be a
Extracts sprites, sounds, textures, and scripts.
The general consensus in the developer community is that using a decompiler to learn from a game you own for personal, educational purposes is a grey but widely accepted practice. Creating and distributing mods for a game, especially one like Undertale whose creators have a known friendly stance towards modding, falls into another grey area. However, redistributing a decompiled project file or claiming decompiled code as your own is almost universally condemned.
While not built-in, some developers use external scripts to obfuscate variable and script names before compiling.