What is it?

UndertaleModTool’s project system is designed to be a more modern way of making mods.

Instead of modding a single data file (and hoping it doesn’t get corrupted), the project system allows you to export all assets you’ve modified to a folder, which can then be re-imported whenever opening the project again.

This provides several benefits:

• The project folder of a mod can be tracked (and backed up) by version control, such as Git.
• Collaboration amongst multiple developers becomes much easier. (Git can be used, again.)
• GML code edits can be preserved in plaintext, rather than always being re-decompiled. Comments work!
• File corruption isn’t quite as disastrous.
• Modded assets can be edited outside of UndertaleModTool, in JSON format (or image/sound formats).
• If you’re lucky, mods can be compatible across multiple game versions.

Want to get started? See the basic setup instructions here.

The project system, as of writing, is currently not feature-complete.

Supported features currently are:

• Exporting and reimporting these assets:
  • Code (GML VM)
  • Game objects
  • Script assets
  • Rooms
  • Sounds
  • Backgrounds (or tilesets)
  • Sprites
  • Sequences
  • Animation curves
  • Fonts
  • Paths
  • Shaders
• Automatic marking of most asset types to be exported when making any changes in the GUI, or when using a built-in importer script.
• Ability to copy assets between projects (manually, outside of UndertaleModTool) to easily port assets between mods and games.
• Ability to edit certain General Info properties, via manual JSON editing.
• Customizing the source (asset) data file path.
• Excluding certain folders (directories) from being imported as assets, if you need to store other JSON files.
  • System folders, hidden folders, and directories beginning with . at the root of the project will be ignored by default.
• Sub-projects, to apply mods to multiple data files (e.g. Deltarune chapters) at the same time.
• BPS file patching, to support legacy mods and to support modifying binary data easily.
• External data file/directory copying and deleting.
• Custom CSX scripts that can be run in multiple stages:
  • Before anything is imported
  • Before assets are imported
  • After everything is imported
• A simple file backup system when installing a mod from a project.
• Ability to recompile all project-touched GML code when saving, to prevent newly-added asset name issues.
• Game version detection and verification when installing a project, via manual JSON editing.
• CLI option to build/install a project, so it can be automated.
• Custom sprite import settings, manually defined in JSON.

Unsupported (but desired/planned) features currently are:

• Remaning CLI options to manage projects.
• Extension asset support.
• More robust code modification, that can be more resilient across game versions:
  • Preprocessor directives (e.g. insert before/after, find and replace)
• Ability to export and import assets outside of a project, but using the same format.
• Ability to duplicate assets, reusing internal project system logic.
• GUI button to reload the entire data file and project in one click.
• Custom texture group support (and their associated settings).
• Custom audio group support.
• Way to mostly automate porting legacy mods to be usable in the project system.

As of writing, documentation on the project system is still expanding.

As for file format/JSON documentation:

• The main project JSON file (project.json) has a basic specification here.
• The optional general-info-options.json file has a specification here.

For a complete view of everything, the C# source code is commented and available within UndertaleModLib’s Project namespace. That can be viewed on GitHub here.