Cobblemon2026-06-18 · 7 min read

How to Fix a Cobblemon Server That Keeps Crashing

Cobblemon crashes are usually one of a handful of known causes — wrong Fabric loader version, too little RAM for the Pokémon data structures, or a mod conflict. Here's how to diagnose and fix each one.

1

Wrong Fabric loader version

Cobblemon requires a specific Fabric loader version that matches its API dependency. A mismatch causes an immediate crash on startup. Fix: check the Cobblemon CurseForge or Modrinth page for the exact Fabric Loader version required for your Cobblemon version and reinstall that loader.

2

Out of memory

Cobblemon loads species data, spawn tables and Pokémon entity models into memory at startup. On 4 GB this is tight; on 2 GB it fails. Fix: increase server RAM to at least 6 GB. Check logs for OutOfMemoryError or java.lang.OutOfMemoryError: Java heap space.

3

Fabric API version mismatch

Cobblemon depends on specific Fabric API features. An outdated or too-new Fabric API causes NoSuchMethodError or ClassNotFoundException crashes. Fix: download the exact Fabric API version listed in Cobblemon's mod dependencies on Modrinth.

4

Conflicting mods

A Pokémon spawn event can conflict with another mod's entity registration. Fix: remove mods one at a time starting with other entity-heavy mods, and check the logs for the mod ID that appears just before the crash.

5

Corrupted world data

A Pokémon entity in a chunk can have corrupted NBT data that crashes the server every time that chunk loads. Fix: identify the crash coordinates from the log, delete the affected region file from world/region/, or roll back from a backup.

6

Java version mismatch

Cobblemon 1.6+ requires Java 21. Older Java (17 or lower) causes UnsupportedClassVersionError on startup. Fix: install Java 21 and point your start script to it.

FAQ

Where are Cobblemon server logs?+
Logs are in the server root at /logs/latest.log. After a crash you can also check /crash-reports/ for a timestamped crash report with a full stack trace.
What Java version does Cobblemon need?+
Cobblemon 1.6 and later require Java 21. If you are running Java 17 or lower you will see UnsupportedClassVersionError on startup.
What is the most common Cobblemon crash cause?+
Wrong Fabric loader version. Cobblemon pins a specific loader version, and using a newer or older loader before the mod is updated for it will crash immediately.
Can mods conflict with Cobblemon?+
Yes, especially entity-heavy mods that register custom spawn events or entity types. Remove added mods one at a time and test after each removal to isolate the conflict.

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