A mod is incompatible
Applies to Forge, NeoForge, Fabric, Quilt.
What it looks like in your log
Incompatible mod set!
What causes it
A mod clashes with your Minecraft version or with another mod.
How to fix it
The log names the mod. Remove or update it to a version that matches your pack.
Why it happens
A mod declared that it cannot run alongside another mod, or alongside this Minecraft version, and the loader honoured the declaration. Mods declare incompatibilities on purpose: two mods that patch the same system, a mod and its own fork, an old version of a library that a newer mod replaces. The log names both sides.
Fix it step by step
- 1Find the pairThe message names the mod and what it conflicts with. On Fabric it reads "is incompatible with"; on Forge the block lists the mod and the incompatible one.
- 2Pick oneTwo mods that do the same job cannot both stay. OptiFine and Sodium, Rubidium and Embeddium, an old library and the mod that replaced it: keep the one the pack was built around.
- 3If it is a version conflict, updateA mod that declares itself incompatible with an older version of another mod is telling you to update that other mod.
- 4Remove the loser and restartDelete the jar from mods/, do not rename it; some loaders still read renamed jars.
If that didn't work
"Failed to create mod instance" without an incompatibility line is a mod crashing on construction, and the stack trace under it names the cause. Often it is a missing dependency reported elsewhere in the same log.
Not sure this is your problem? Paste your log and Roastd will tell you which of these it actually matched, and what else it found.
Check your own log