Mixin failures

java.lang.ClassNotFoundException: org.spongepowered.asm.launch.MixinTweaker

What the log looks like

java\.lang\.ClassNotFoundException:\s*org\.spongepowered\.asm\.launch\.MixinTweaker

How to fix it

  1. Open your latest launch log and look just above `Unable to launch` for `Loading tweaker org.spongepowered.asm.launch.MixinTweaker from <Mod>.jar` to find which mod requested Mixin.
  2. Check that mod's official download page for required dependencies and install a standalone Mixin loader mod for your Minecraft version (such as MixinBooter or UniMixins on Forge 1.12.2).
  3. If you compiled the mod from source yourself, delete your custom JAR and download an official release build instead—or rebuild it using the project's shaded build task (such as `./gradlew shadowJar`) so Mixin classes are included.
  4. If you are using MultiMC or another third-party launcher and the Mixin classes are already inside the JAR, make sure your Minecraft folder path contains no exclamation marks (`!`) and try recreating the instance or testing in the vanilla launcher.
LoadersForge, Server
SeverityStops the game
CategoryMixin failures

Check your own log

Related errors

Mixin failures3D Skin Layers Crash: Cannot Invoke Mesh.setPosition Because "mesh" Is NullUpdate the 3D Skin Layers (skinlayers3d) mod—and Sodium if you have it installed—to the latest release for youMixin failuresCritical injection failure — a mixin could not find its targetTwo mods are usually fighting over the same game methodMixin failuresInvalidMixinException: Mod Mixin Failed to ApplyOpen your latest.log or crash report and look for 'Mixin apply for mod' or the 'Config :' line inside the 'InvMixin failuresInvalidMixinException: Unexpecteded ClassMetadataNotFoundExceptionFind the line saying 'Mixin apply for mod <modname> failed' or 'from mod <modname>' right above the error in yMixin failuresMatrixStack Underflow Crash (NoSuchElementException in ArrayDeque.getLast)Look at the line immediately below class_4587 or MatrixStack in the crash log for a Mixin tag formatted like hMixin failuresMixin Transformation of net.minecraft.client.main.Main FailedOpen latest.log or the launcher crash output and look at the Caused by lines below Mixin transformation of net