Mod conflicts

LinkageError: Loader Constraint Violation on LogUtils.getLogger (SLF4J Conflict)

What it looks like in the log

java.lang.LinkageError: loader constraint violation: when resolving method 'org.slf4j.Logger com.mojang.logging.LogUtils.getLogger()' the class loader

How to fix it

  1. If you have Iris Shaders installed, update it to the latest release specifically marked for your exact Minecraft version (such as 1.18.2 or newer), as early Iris builds bundled SLF4J.
  2. Update Fabric Loader in your launcher profile to the latest available version.
  3. Check your `mods` folder for mods built for Minecraft 1.18.1 or older and update or remove them.
  4. If the game still fails to launch, temporarily move half of your mods out of the `mods` folder and test launch repeatedly (binary search) to identify and remove the specific mod bundling `org/slf4j` classes.
LoadersFabric, Quilt
SeverityStops the game
CategoryMod conflicts

Check your own log

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