My server won't start or crashes with a specific modpack — help?
Modpacks are wonderful until one refuses to boot. The good news is that modpack crashes almost always leave a clear trail in the Console, and a short checklist resolves the majority of them. Here's how to work through it.
Read the crash report first
When a modded server crashes on start, the Console or crash report usually names the exact problem — a specific mod, a missing dependency, or an out-of-memory error. Start there before changing anything.
Step-by-step
- Read the Console/crash report — it usually names a mod or a missing dependency.
- Confirm the loader version (Forge/Fabric build) matches what the pack requires.
- Make sure you have enough RAM — big packs OutOfMemory-crash below their recommended floor (see our modded sizing article).
- Use the server pack, not the client pack — client-only mods crash a server.
- Share the log via mclo.gs and open a ticket if you're still stuck.
Tip: A large modpack that keeps crashing on start is very often simply out of memory. Check the Startup tab's RAM settings against the pack's recommended minimum before assuming a mod is broken.
Frequently asked questions
How do I know it's a RAM problem? Look for "OutOfMemory" or a heap error in the Console. Big packs need a lot of RAM — a Supreme or Ultimate plan is recommended for heavy packs.
The report names a mod — what do I do? Check that mod's version against the loader, remove or update it, and try again. A missing dependency is fixed by adding the mod it asks for.
Still crashing after all this? Share your crash log via mclo.gs and open a ticket. Our team can read it and point to the cause.