How to fix "incompatible mod" errors or crashes while loading mods

1. Where to find crash information

When the server crashes on startup, Minecraft usually generates two useful kinds of file:

• logs/latest.log — the full record of what happened up to the crash.
• crash-reports/crash-*.txt — a detailed error report, usually easier to read.

Open these files from the panel's Files tab.

2. Checking the Forge/Fabric/NeoForge version

The most common cause of crashes is a version mismatch:

• Check that the mod was made for the same Minecraft version installed on the server (e.g. a 1.20.1 mod on a 1.21 server won't work).
• Check that the mod is for the right loader — a Fabric mod doesn't work on a Forge server, and vice versa.

3. Missing dependencies

Many mods depend on extra libraries to work. The most common are:

• Fabric API (required by most Fabric mods).
• Forge Config API Port, Architectury API, Cloth Config (used by many multiplatform mods).

In the crash-report, look for messages like:

  Mod X requires Y, which is missing

This tells you exactly which dependency needs to be installed in the mods folder.

4. Client-side mods running on the server

Some mods are client-only (e.g. UI mods, shaders, minimaps) and shouldn't be put on the server — this usually causes an immediate crash on startup.

5. Finding which mod is causing the problem

In the crash-report, look for the "Affected Mods" section or the stack trace, which usually shows the culprit mod's name near the start of the error.

If it's not clear, use the bisection method:

1. Remove half of the mods from the mods folder (move them to another folder, don't delete them).
2. Restart the server.
3. If the error goes away, the problem mod is in the group you removed — repeat by splitting that group in half.
4. If the error persists, the problem is in the group that stayed — repeat the process.

6. Conflicts between mods

Two mods can conflict when they change the same thing in the game (e.g. two mods that modify world generation). In that case:

• Check whether there's a compatibility version between them (many popular mods release "compat patches").
• Check the mod's page on CurseForge/Modrinth for known incompatibility warnings.

7. The most common fixes

• Update the mod to the latest version compatible with the server.
• Install the missing dependency.
• Remove client-side mods from the server folder.
• Reinstall Forge/Fabric if the loader files are corrupted.