MPatcher
by KSmc's Team
MPatcher lets a modder define changes to Minecraft's own classes by writing JSON files instead of hand-coding bytecode transformers.
What it does
The mod works in two stages. First it loads itself as a Java agent before the mod loader starts, then it loads custom classes and registers a class file transformer that re-transforms the game classes listed in a set of configuration files. Each entry names a class, such as net.minecraft.client.gui.Gui or net.minecraft.world.entity.player.Player, and points to a source file that replaces or patches it. The mod appears in the mod list and runs under NeoForge, Forge and Fabric.
The configuration lives in the mod's own folders: custom class files go into the mp-classes folder inside the game directory, and the export settings are kept in mp-exports/mp-export-config.json. Each transformation is described by a URL that points to one of these JSON files, and the mod reads them when the game loads. Players and modders who do not know which classes to target can enable the debug export feature, which writes the classes to the mp-exports folder, and press F12 to open the Recaf app and browse them.
Builds are published for Fabric, Forge and NeoForge, with the latest file, 1.1 for 1.21.11, dated 2026-02-20. Either side can run it, and neither needs it. The code is released under the MIT License and is open source.
Key features
JSON-defined class patches
Changes to game classes are described in JSON files that point to class sources, so no transformer code has to be written.
Class export for reference
A debug option writes the game classes to the mp-exports folder so modders can see what they are changing.
Recaf integration
Pressing F12 opens the Recaf application to inspect classes without leaving the game.
Custom class loading
Custom class files placed in the mp-classes folder are loaded alongside the transformed game classes.
Compatibility
Latest build for each game version and loader.
1.21.x12 of 12 versions with builds
Only full game releases are shown. This mod publishes no snapshot builds.
How it compares
Client Export Helper is a Fabric-only, client-side mod for 1.21 – 1.21.11, released under the GNU General Public License v3.0 or later and open source. Scelli is a server-side mod for Fabric covering 1.21.8 – 1.21.11, released under the MIT License and open source. Where MPatcher works on Forge and NeoForge too, both alternatives are limited to Fabric.
| Mod | Loaders | Game versions | Environment | Updated |
|---|---|---|---|---|
| MPatcher | Fabric, Forge and NeoForge | 1.21 – 1.21.11 | Client or server, optional | 2026-02-20 |
| Client Export Helper | Fabric | 1.21 – 1.21.11 | Client-side only | 2025-09-14 |
| Scelli | Fabric | 1.21.8 – 1.21.11 | Server-side only | 2026-02-26 |
Questions
Which loaders does MPatcher support?
Does a server need MPatcher installed?
Where do the class names come from?
Which Minecraft versions have files?
In the catalog
MPatcher is one of 3,514 Library mods on ModsFinder, and one of 2,348 Library mods for Fabric. 19,862 mods support Minecraft 1.21.11.
More from KSmc's Team
Similar mods
What the author says
If you want to retransfrom game's codes, you need to add some class files to the "mp-classes" folder in the game directory. They will be loaded and retransfromed to the game. If you think it is too rigmarole to retransfrom codes,you can just write one or more jsons into the "mp-classes",then write some url(s) such as…
Official listing
- Modrinth page
- modrinth.com/mod/minecraftpatcher
- Owner
- KSmc's Team
- Published
- 2026-02-13
- Updated on Modrinth
- 2026-02-20
- Facts verified
- 2026-10-15