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Forge Mod Installed on Fabric

A Forge mod was installed on a Fabric server, which cannot load it. Fabric does not understand Forge's mod format, so the jar is rejected as not a Fabric mod.

What does this error mean?
'Not a Fabric mod' means a Forge-format mod was placed on a Fabric server. Fabric looks for fabric.mod.json and finds Forge metadata instead, so it does not recognize the jar as loadable. 
Not a Fabric mod
Most Common Causes
  • Downloading the Forge build of a mod for a Fabric server.
  • Confusing Forge and Fabric versions.
  • Mixing loaders in the mods folder.
  • Assuming cross-loader compatibility.
  • Choosing the wrong file on a multi-loader page.
How To Diagnose
  1. Confirm the server runs Fabric.
  2. Check the jar, a Forge mod has mods.toml, not fabric.mod.json.
  3. Read the log for the rejected mod.
  4. Verify you downloaded the Fabric build.
Recommended Fixes
  • Install the Fabric build
    Download the Fabric version of the mod for your Minecraft version.
  • Use Sinytra Connector (carefully)
    Some setups run certain Forge mods on Fabric via Connector, but support is limited, prefer native Fabric builds.
  • Run a Forge server instead
    If you need that specific Forge mod, run Forge rather than Fabric.
  • Pick the right file
    Select the Fabric download on the mod page.
Analyze My Log
Frequently Asked Questions

Not natively. Forge mods use a different format Fabric does not read.

Sinytra Connector can run some Forge mods on Fabric, but it is limited, native Fabric mods are safer.

Fabric mods contain fabric.mod.json, Forge mods contain mods.toml/Forge metadata.