Mod Compatibility Issues
Having trouble with mods not working together? Here's how to diagnose and fix compatibility problems.
Common Compatibility Rules
1. Forge mods don't work with Fabric (and vice versa)
2. Mod version must match your Minecraft version
3. Server and client mods must be identical
4. Dependencies must be installed too
Error Types & Solutions
"Mod mismatch" / "Missing mods" when connecting
Cause: Your client mods don't match the server mods.
Solution:
- Get the exact modpack/mods from your server owner
- Install them using CurseForge or Prism Launcher
- Make sure versions match exactly
Use the Modpack Sync feature in the panel to generate a link your players can use to download all mods!
"Missing required mod: X"
Cause: A mod needs another mod (dependency) to work.
Solution:
- Read the error - it tells you what's missing
- Download the missing mod from CurseForge or Modrinth
- Add it to the mods folder
- Restart the server
Common dependencies:
| Dependency | Required by |
|---|---|
| Fabric API | Almost all Fabric mods |
| Architectury API | Many cross-platform mods |
| Cloth Config | Mods with config screens |
| GeckoLib | Mods with custom animations |
| Kotlin for Forge | Kotlin-based Forge mods |
"Incompatible mod set"
Cause: Two mods are known to conflict with each other.
Solution:
- Check both mods' pages for known incompatibilities
- Choose one mod or the other, not both
- Look for compatibility patches on CurseForge
"Duplicate mods"
Cause: Same mod is installed twice (different versions).
Solution:
- Go to Files →
mods - Look for mods with similar names
- Delete the older/duplicate version
"Unsupported Fabric Loader version"
Cause: Mod needs a newer Fabric Loader version.
Solution:
- Go to Startup
- Update the Fabric Loader version
- Reinstall the server or download new launcher files
Forge vs Fabric
These are the two main mod loaders. They are NOT compatible with each other.
| Feature | Forge | Fabric |
|---|---|---|
| Mod library | Huge (10+ years of mods) | Growing fast |
| Update speed | Slower | Very fast |
| Performance | Good | Excellent |
| Popular for | Tech mods, kitchen sinks | Optimization, newer mods |
Never put Forge mods in a Fabric server or vice versa. They will crash.
Version Mismatches
The most common compatibility issue is version mismatch.
How to check versions:
- Find your server's Minecraft version in Startup
- Check your server's mod loader (Forge/Fabric) and its version
- Make sure EVERY mod supports that exact Minecraft version
Example:
Server: Minecraft 1.20.1 + Forge 47.2.0
Mod: "Create" for Minecraft 1.20.1 Forge ✅
Mod: "Create" for Minecraft 1.19.2 Forge ❌ (wrong MC version)
Mod: "Create" for Minecraft 1.20.1 Fabric ❌ (wrong loader)
Client-Side vs Server-Side Mods
Some mods only need to be installed on one side:
| Type | Install on | Examples |
|---|---|---|
| Client-only | Your PC only | Optifine, shaders, minimaps, Sodium |
| Server-only | Server only | Some admin/utility mods |
| Both required | Server AND client | Most gameplay mods (Create, Cobblemon, etc.) |
Check the mod's description on CurseForge/Modrinth - it usually says if it's client-side, server-side, or both.
Binary Search Method
If you can't figure out which mod is causing problems, use binary search:
- Remove half of your mods
- Test if the server starts
- If it works, the problem is in the removed half
- If it still crashes, the problem is in the remaining half
- Repeat until you find the bad mod
This is much faster than removing mods one by one!
Getting Help
When asking for help with mod issues, include:
- Your Minecraft version
- Your mod loader (Forge/Fabric) and version
- List of installed mods
- The exact error message or crash log
- What you were trying to do when it happened
Join our Discord and we'll help you sort it out!