Mixin apply failed: reading the crash and finding the mod

Mixin apply failed and Critical injection failure crashes name the mod in the mixin config line, not the stack trace. Here is how to read one and what to do next.

The short version

A "Mixin apply failed" crash means one mod tried to patch a class another mod had already changed, or patched a version of the game it was not built for. The mod named in the mixin config line is the one to remove or update. It is almost never the mod named in the stack trace below it.

A mixin crash reads like a wall of noise and contains exactly one useful line. Finding that line takes about twenty seconds once you know where to look.

#What a mixin actually is

Mods cannot edit Minecraft's code directly, so they patch it at load time. Mixins are the mechanism: a mod declares "insert this code at the start of this method" and the loader applies it while the game boots.

This works remarkably well until two mods patch the same method, or a mod patches a method that changed shape in a Minecraft update. Then the patch cannot be applied, and because a half-patched class is worse than no class at all, the game stops.

#Finding the mod in ten seconds

Search the crash for mixins. and you will find a line like:

Mixin apply failed mixins.examplemod.json:MixinServerPlayer -> net.minecraft.server.level.ServerPlayer

The part before the colon, mixins.examplemod.json, is the mod doing the patching. That is your culprit. The part after the arrow is the vanilla class it was trying to patch, and it is never the problem, though it is the part people quote when asking for help.

Other phrasings of the same thing:

Critical injection failure: ... in mixins.examplemod.json
Mixin transformation of net.minecraft.something failed
@Inject annotation on methodName could not find any targets

All of them name a mixin config. All of them mean the same thing: that mod's patch did not fit.

#The three causes, in order of likelihood

1. The mod is built for a different Minecraft version. The most common cause by a distance. A mixin written for 1.20.1 targets a method signature that may not exist in 1.21. The mod loads, tries to patch something that has moved, and fails.

Check the mod's download page for a build matching your exact Minecraft version and loader. Not "1.21.x" if you are on 1.21.4; mixin targets are precise.

2. Two mods patching the same method. Both are correct in isolation and incompatible together. This is common with performance mods, which patch the same hot paths everyone else wants to patch.

The tell is a mixin failure that only appears when both mods are present. Remove either one and it goes away.

3. A missing dependency. Some mixins target classes added by another mod. If that mod is absent, the target does not exist and the injection fails with "could not find any targets".

#What to do

Find the mixin config name in the crash.
Match it to a mod jar in /data/mods. The name usually matches obviously; if not, open the jar's mods.toml or fabric.mod.json.
Check the mod's page for a build matching your Minecraft version and loader exactly.
If it is already current, remove it, restart, and confirm the server boots. That tells you whether you have found the whole problem.
If the server boots without it, search the mod's issue tracker for the other mod's name. Known incompatibilities are usually already reported by somebody who had the same evening you are having.

#When it is a modpack

If you are running a pack rather than a hand-picked mod list, do not start removing mods. The pack author has tested the combination and a mixin failure usually means something else has drifted.

Check in this order: are you on the pack version you think you are, did anything get added to /data/mods outside the pack, and is there a newer pack release fixing exactly this. Reinstalling the pack at a known version is faster than debugging someone else's mod list.

#Why the server stops rather than carrying on

Occasionally people ask whether the failed patch can just be skipped.

It can, technically, and it is a bad idea. A mod whose patch did not apply is running with the assumption that it did. The result is not a missing feature, it is a mod operating on a game that does not behave the way it expects, and the crash you get instead arrives later and makes far less sense.

#Frequently asked questions

What does Mixin apply failed mean in Minecraft?

A mod tried to modify a game class at load time and could not. Either another mod had already changed the same method in an incompatible way, or the mod was built against a different Minecraft version than the one you are running. The server stops rather than continue with a half-patched class.

Which mod is actually causing a mixin crash?

The one named in the mixin config file, which appears as something like mixins.examplemod.json in the error. That is the mod doing the patching. The class named further down the stack trace is what it was patching, which is usually vanilla Minecraft and never the culprit.

How do I fix Critical injection failure?

Update the mod named in the mixin config to a build matching your Minecraft version and loader. If it is already current, you have a genuine conflict between two mods patching the same method, and one of them has to go. The mod's issue tracker usually has the pairing listed already.

Written and maintained by the Hostd engineering team. Last updated 2026-08-05. Notice a mistake? Tell us.