Wrong mod loader

ClassTweakerFormatException: Namespace (named) Does Not Match Runtime (intermediary)

What it looks like in the log

net.fabricmc.loader.impl.lib.classtweaker.reader.ClassTweakerFormatException: Namespace (named) does not match current runtime namespace (intermediary

How to fix it

  1. Check the crash log for the line 'Failed to read classTweaker file from mod <mod_id>' to identify the broken mod.
  2. Open your Minecraft 'mods' folder and remove that mod's JAR file (especially if its filename ends in '-dev.jar' or '-sources.jar').
  3. If you downloaded the mod online, return to Modrinth or CurseForge and download the main release JAR instead of a development or source artifact.
  4. If you are developing this mod yourself, build it by running './gradlew build' (or the 'remapJar' task) rather than the 'jar' task, and copy the standard JAR from 'build/libs/' without the '-dev' suffix, plus ensure 'accessWidenerPath' is configured in your 'build.gradle' loom block.
LoadersFabric
SeverityStops the game
CategoryWrong mod loader

Check your own log

Related errors

Wrong mod loaderAccessWidenerFormatException: Namespace (named) does not match current runtime namespace (intermediary)Check the crash log for the line 'Failed to read accessWidener file from mod <modname>' to identify the brokenWrong mod loaderFabric Crash: Failed to Read classTweaker File (Namespace Mismatch)Look at the line 'Failed to read classTweaker file from mod <modid>' in your crash log to identify the offendiWrong mod loaderFabric mod dropped into a Forge or NeoForge instanceA Fabric jar has fabric.mod.json; Forge/NeoForge want META-INF/mods.tomlWrong mod loaderFailed to read accessWidener file: Namespace (named) does not match (intermediary)Open your instance's 'mods' folder and find the mod named in the error message (for example, 'iris').Wrong mod loaderFailed to read classTweaker file from mod (Namespace Mismatch)Find the broken mod's ID right after 'Failed to read classTweaker file from mod' in the error log.Wrong mod loaderForge mod dropped into a Fabric instance (and the other way round)Forge and Fabric jars are not interchangeable — the file names often look identical