Getting Started

This page gives UndertaleModTool download and installation instructions, and how to get started using the tool.

The latest stable UndertaleModTool release can be found here.

These versions are generally well-tested, but they may not always have support for the latest GameMaker features.

Important

Unless you know how to use a command-line interface, you probably don’t want to use the “CLI” version of the tool. Just download a regular version with the full UndertaleModTool name.

The most recent nightly (bleeding edge) release can be found here.

These versions are more likely to contain stability issues, as they include the very latest code changes. However, they may have support for more recent/obscure GameMaker features, and more niche fixes and features.

After downloading the tool, you can then use it to open certain GameMaker data files. Commonly, this means data.win or game.unx, but there are several other file types and names.

Upon opening a data file, you can view and edit its contents directly, and if you wish, save back your modified data file. The game, with modified changes, can then be played.

Important

It is highly recommended to make frequent backups of these data files, before making any changes. The modding interface can lead to data corruption, if used incorrectly.

Currently, this site is lacking more advanced usage details. Please consult other public resources, the Underminers Discord server, or if you would like to contribute information to this site, make a pull request!

If you encounter any issues with the tool itself, feel free to report them using GitHub issues. This lets us track and work on problems effectively.

If you need general assistance, sometimes GitHub issues are fine, but generally you may find better help at the Underminers Discord server.