Minecraft Server Won't Start: How to Read the Crash Log

If your server shows Offline and won't boot, the fix is almost never a guess. It's in your Console. Open Console from the left sidebar and read the last 10-20 lines before it stops. That text tells you exactly what broke: a missing mod dependency, a client-side mod uploaded by mistake, a bad Java version, or a corrupted world. Fix that one named thing and restart.

Symptoms

• Status pill stays on Offline or flips back to it seconds after you hit Start
• Console ends with a stack trace, "missing dependency," or a mod name followed by an error
• Server was fine, then stopped starting right after you added/removed mods, changed version, or reinstalled

Why this happens

Support tickets show the same handful of root causes over and over:

• Missing mod dependencies. Mods like Supplementaries, BiomesOPlenty, or RightClickHarvest require a library mod (Moonlight Lib, TerraBlender, GlitchCore, corelib) that wasn't installed. Removing a mod others depend on breaks the chain too.
• Client-side mods uploaded to the server. Mods like Embeddium, Oculus, Sodium, or Hold My Items only work on the player's game, not on a dedicated server. Dropping them in the mods folder crashes boot.
• Not enough memory. Big modpacks need more RAM than small plans provide. The Console will say it ran out of memory.
• Wrong or missing startup script. Legacy versions like 1.12.2 Forge sometimes need a specific startup configuration.
• Corrupted world. Reinstalls, bad addon combos, or interrupted seed changes can brick the world folder itself.
• Duplicate mods from a messy modpack update can also block startup.

How to fix it

1. Open Console and read the actual error at the bottom of the log: note the exact mod or class name mentioned.
2. If it names a missing dependency, install that specific dependency through Mods Installer (individual mods) or Modpack Installer (full packs): not both mixed together.
3. If the error says a mod "cannot be loaded on a dedicated server," it's client-side only: delete it from Files and keep it on your local client instead.
4. If the log mentions memory, see how much RAM your modpack needs.
5. If none of the above applies and the log points at world data, restore a recent snapshot from Backups.
6. Restart the server and re-check Console: repeat for any new error, since dependency chains can surface one at a time.

Add mods a few at a time and test between each one. Bulk-adding a modpack's worth of mods manually is the #1 cause of unreadable crash logs.

Still stuck?

If the Console log doesn't clearly name the problem, or you're facing a startup script issue on a legacy version, open a support ticket with the last 30 lines of your log, staff can pinpoint it fast. See also Fix "Missing Dependency" and Mod Conflict Errors, How to Install a Modpack on Your Minecraft Server, How to Change Your Minecraft Server Version, and How Much RAM Does Your Modded Minecraft Server Need?.