Launcher problems

Missing Log4j Library on Launch (LogManager ClassNotFoundException)

What it looks like in the log

java.lang.ClassNotFoundException: org.apache.logging.log4j.LogManager

How to fix it

  1. Launch a clean Vanilla profile of the exact same Minecraft version once before starting your modded profile so the launcher downloads all required base libraries.
  2. Use your launcher's Repair or Verify option—or manually delete the libraries/org/apache/logging/log4j folder inside your launcher data directory—to force a fresh download of Log4j.
  3. Update your third-party launcher (such as HMCL or GDLauncher) to its latest release to fix bugs where base game libraries are omitted from the launch command.
  4. If every instance in your launcher fails with this error, back up your worlds and mods, then completely reinstall the launcher to rebuild its corrupted shared files.
LoadersFabric, Forge, Vanilla
SeverityStops the game
CategoryLauncher problems

Check your own log

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