Missing Mod / Dependency
A modded server stops during loading because one of your mods needs another mod that is missing or the wrong version. The crash report names exactly what is required, which makes this one of the easier modded errors to fix once you know where to look.
What does this error mean?
Mods declare dependencies, other mods or libraries they cannot run without. When a required mod is absent or its version does not satisfy the range requested, the loader refuses to continue and lists the missing dependency and the version it expects.
Mod X requires Mod Y
Most Common Causes
- A required library mod (Fabric API, Architectury, Cloth Config, etc.) is not installed.
- The dependency is present but the wrong version for the requested range.
- A client-only dependency was never added to the server.
- Mod and dependency are built for different Minecraft or loader versions.
- A modpack was copied without all of its library mods.
How To Diagnose
- Read the crash report or log for 'Missing or unsupported mandatory dependencies'.
- Note the exact mod id and version range it asks for.
- Check your mods folder for that mod id and its installed version.
- Confirm every mod targets the same Minecraft + loader version.
Recommended Fixes
- Install the named dependency
Download the exact mod and version from CurseForge or Modrinth and drop it in mods/. - Match the version range
If installed but rejected, replace it with a build inside the requested version range. - Add core libraries
Many Fabric mods need Fabric API. Many Forge/NeoForge mods need Architectury or a config lib. - Use the full pack
When running a modpack, install it complete rather than picking individual jars.
Frequently Asked Questions
The mod's CurseForge/Modrinth page lists required mods. Match your Minecraft and loader version.
For most gameplay mods, yes. Mismatched versions cause join-time disconnects.
Install the latest build for your exact Minecraft version, that is almost always correct.