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.
Modpacks are the most memory-hungry thing we host, and one that will not start is usually short of RAM rather than broken. Our Supreme and Ultimate Minecraft plans are the ones sized for heavy modpacks.