Corrupted files

NoClassDefFoundError: org/objectweb/asm/ClassVisitor on Launch

What it looks like in the log

java.lang.NoClassDefFoundError: org/objectweb/asm/ClassVisitor

How to fix it

  1. If you use a third-party launcher (such as HMCL) with a custom download mirror enabled, switch the download source back to the official source in your launcher settings.
  2. Delete the .minecraft/libraries/org/ow2/asm/ folder (or use your launcher's option to delete all library and cache files for the instance) and launch the game again so fresh copies are downloaded.
  3. If the error persists, delete the broken game version profile and reinstall Fabric, Forge, or OptiFine using your launcher's built-in installer to regenerate a clean version JSON file.
LoadersFabric, Forge, Quilt, Vanilla
SeverityStops the game
CategoryCorrupted files

Check your own log

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