Older tools like GMDS exist but struggle with GMS2 versions 2.3+ (which introduced significant changes to how variables and functions are stored). If UndertaleModTool fails, these are worth a look, but they are largely obsolete for modern GMS2 games.
This is an open-source tool designed to interact with GameMaker data files. gamemaker studio 2 decompiler
When you build a game in GMS2, the IDE compiles your project into a platform-specific executable: Older tools like GMDS exist but struggle with
A decompiler is a type of software that takes compiled code and converts it back into a higher-level programming language, making it more readable and understandable for humans. This process is also known as reverse engineering. Decompilers are often used to analyze malware, understand software vulnerabilities, or recover lost source code. these are worth a look