Minecraft Log Analyzer

Port is already in use

Another program is already listening on the Minecraft port (usually 25565 for Java, 19132 for Bedrock). The server can't start while the port is occupied.

EULA not accepted

Mojang requires you to explicitly accept the Minecraft End User License Agreement before running a server. The server creates an eula.txt on first run with `eula=false`.

Java version too old

Your Java runtime is older than what this server jar requires. Minecraft 1.17–1.17.1 needs Java 16+, 1.18+ needs Java 17+, and 1.20.5+ needs Java 21+. Older Java can't load newer class files.

Out of memory — JVM exhausted heap

The JVM ran out of heap memory. Java silently dropped or crashed. Common causes: too many chunks loaded, too many entities, memory-hungry mods, or heap size set too low for your world/modpack.

Server watchdog forced shutdown

The server tick (normally 50ms) took too long, and the Watchdog thread forcibly killed the server. This usually means a mod or plugin is doing heavy work on the main thread, an infinite loop, or chunk generation is too slow.

Server can't keep up — TPS below 20

The server can't process all 20 ticks per second. Players will see lag, entities will stutter, and mob AI slows down. This is a performance issue, not a crash.

Missing mod dependencies

A mod requires another mod that isn't present or is the wrong version. Forge/Fabric will refuse to start until dependencies resolve.

Plugin failed to load

A plugin failed to load, usually because of a version mismatch, a missing dependency, or the plugin jar is corrupted.

Ticking entity / block entity crash

A specific entity or block entity threw an exception during its tick. This is the single most common modded-server crash. The log's stack trace will name the exact entity or tile entity class — that identifies the misbehaving mod.

Mixin apply failure (Fabric/NeoForge)

A Fabric or NeoForge mod failed to apply its Mixin transformers. Mixin is how these mods hook into Minecraft's code — when it fails, it usually means two mods are trying to modify the same code in conflicting ways, or one mod's Mixin is incompatible with your Minecraft version.

NoClassDefFoundError / NoSuchMethodError — mod version mismatch

A mod is calling a class / method / field that doesn't exist. This almost always means the mod was built for a DIFFERENT version of Minecraft or a different dependency than you have installed — common when mixing 1.20.1 mods on 1.20.4 or when a required library mod is a different version than the mod expects.

Duplicate mod detected

Two copies of the same mod are in your /mods folder. This is almost always caused by updating a mod without removing the old jar — both end up loaded, and the mod loader refuses to start.