What are Crash Logs in Minecraft? Everything You Need to Know.

Crash logs (or crash reports) are detailed files generated automatically whenever your Minecraft server or client crashes. They live in the crash-reports/ folder inside your server directory (where all the other files are, like world, server.properties, etc.). Each crash log is timestamped with the exact date and time of the crash, making it easy to find the most recent disaster.

Think of a crash log as a black box recorder for your server. It captures what was happening at the moment everything went sideways: which mods were loaded, what plugin, datapack or mod was running, and where things broke.

Key Components of a Crash Log

Stack Trace

This is the heart of every crash log. It's a chronological list of what your server was doing right before it crashed. You'll see a bunch of lines starting with "at" followed by code paths. The top of the stack trace usually points to the immediate cause – look for mentions of specific mods, plugins, or error types like NullPointerException or ClassNotFoundException.

Error Message

Right above or within the stack trace, you'll often see a plain-English (or close to it) description of what went wrong. Examples:

• Missing mods
• Mod X requires Mod Y version Z
• Ticking entity

This is your quickest clue.

Mod States (U, L, C, H, I, J, A, D, E)

If you're running Forge or similar mod loaders, you'll see cryptic letters next to each mod. These show how far each mod made it through the loading process before the crash:

• U = Unloaded
• L = Loaded
• C = Constructed
• H = Pre-initialized
• I = Initialized
• J = Post-initialized
• A = Available
• D = Disabled
• E = Errored

If you see UCE, it means that mod unloaded, constructed, then errored, pinpointing the culprit.

System Details

The second half of the crash log shows your Java version, allocated RAM, operating system, and full mod list with versions. This section is gold when you're asking for help as it tells others exactly what environment you're running.

Common Crash Causes

• Missing or mismatched mod versions: The crash log will usually say something like "Mod X needs Mod Y version 1.5.2".
• Incompatible mods: Two mods trying to modify the same game behavior.
• Ticking entity errors: A specific mob or block is causing repeated failures every game tick.
• Out-of-memory errors: Your server ran out of RAM mid-operation.

How to Use Crash Logs

1. Open the most recent file in crash-reports/ (sorted by date).
2. Read the error message near the top of the general idea.
3. Scan the stack trace for mod names or familiar keywords.
4. Check mod states to see which mod failed to load.
5. Google the error or share the full crash log on forums for help.

Why Crash Logs Matter

Crash logs aren't just for developers. Any server admin can use them to diagnose problems faster than trial-and-error. They turn "my server won't start" into "Mod XYZ is missing a dependency" which saves you hours of guessing.