How to Fix a Mixin Crash Caused by MixinBooter

Read the Crash Report First

When a mod fails to apply its bytecode transformations, the game usually crashes during startup with a stack trace mentioning mixin, MixinBooter, or a specific @Mixin target class. Open your crash log and scroll to the top of the stack trace. Look for the line that names the mixin config file (often ending in .mixins.json) and the mod it belongs to. That tells you which mod is the actual culprit, not MixinBooter itself.

Narrow Down the Conflict

MixinBooter exists to let other mods apply transformations at runtime, so a crash here almost always means two mods are fighting over the same class. Common causes:

• Two mods both mixin into the same vanilla or modded class.
• A mod expects a class that another mod removed or renamed.
• A mod's mixin config is being loaded before its dependency is ready.

Practical Steps

1. Note the mod name from the crash trace.

2. Temporarily remove that mod and relaunch to confirm it is the trigger.

3. Check whether a newer build of that mod exists that plays nicely with your other mods.

4. If two mods conflict, look for a config option in either mod to disable the overlapping patch.

5. Re-add mods one at a time so you can pinpoint the exact pair causing the failure.

Do not edit MixinBooter's own files; it is a library and the fix belongs with the mods using it.