Fixing Minecraft Server Crashes
The five most common causes of a Minecraft server crash, and what you can actually do about each one here.
Out of Memory
Error: java.lang.OutOfMemoryError: Java heap space. The server ran past its heap ceiling.
The heap is sized by the platform, from the host your server is on. There is no RAM allocation field in Settings, and there is no startup script for you to edit on Vanilla, Paper or Fabric.
The ceiling is generous by design - the platform gives roughly half of what is free on the host after a reserve, clamped between 2 GB and 12 GB - and the JVM only commits what it actually uses. A server that needs 2 GB uses 2 GB.
On Forge and NeoForge you can raise your own ceiling: put an -Xmx line in user_jvm_args.txt at the server root, editable from the Files tab. Because Java takes the last occurrence of a repeated option, your value wins over the platform's. Do not add -XX:+AlwaysPreTouch alongside it - see Aikar's Flags.
On Vanilla, Paper and Fabric there is nothing to raise from your side. If you are hitting the ceiling repeatedly, open a support ticket with the error and the Resource Usage figures from the Overview tab.
Before assuming you need more memory, check for a leak. On Paper, spark's /spark heapsummary shows what is holding the heap. Common culprits are map-rendering plugins, item-frame maps, chunk loaders and plugins that hold references they never release.
Wrong Java Version
Error: UnsupportedClassVersionError.
All five server types here run Minecraft 26.2 on Java 25, installed and selected by the platform. There is no Java version to choose.
So this error on a GameGrid server points at a plugin or mod compiled against something newer than Java 25, not at the server. Remove the .jar you added last.
Older guidance about Java 8, 17 and 21 is about older Minecraft versions and does not describe this platform.
Broken Plugin or Mod
The crash report normally names the plugin or mod. Look for its name or package in the stack trace.
Stop the server, remove the .jar from plugins/ (Paper) or mods/ (Fabric, Forge, NeoForge), and start again. A clean start confirms it.
To find it when the report is unhelpful: move everything out of the folder, start clean, then add back a few at a time with a restart between batches.
Update the add-on to a build for Minecraft 26.2 and your loader, or find an alternative. The Mods tab's marketplace search is already scoped to your server type, which removes one whole class of mistake.
Corrupted World Files
Symptoms: the server crashes loading one area, or players crash entering certain chunks.
Restore from the Backups tab. That is the safest fix and it is what the automatic daily backups are there for. The platform stops, restores and starts the server for you, and copies the current state first so the restore is reversible.
Without a backup, you can delete an individual region file. They are at world/region/, named r.X.Z.mca - divide a block coordinate by 512 and round down to get X and Z.
Deleting a region file removes every block, entity and block entity in that 512 x 512 area. It regenerates fresh, and anyone standing there is moved to spawn.
Where the Nether and the End are depends on the server type. On Paper they are separate top-level folders - world_nether/ and world_the_end/ - each with its own region/. On Vanilla, Fabric, Forge and NeoForge they are inside world/, as DIM-1/region/ and DIM1/region/.
Take a manual backup before deleting anything.
Watchdog Crashes
Error: "A single server tick took 60.00 seconds". The watchdog killed the process because one tick never finished.
That is almost always an infinite loop in a plugin or mod, or an enormous redstone contraption.
The thread dump in the crash report shows what was stuck. Look for a plugin or mod package name in it.
On Paper, setting redstone-implementation to ALTERNATE_CURRENT in config/paper-world-defaults.yml is the standard fix for redstone-driven tick blowouts. That file only exists on Paper.
max-tick-time in Settings (default 60000 ms) is how long a tick may run before the watchdog acts. Raising it hides the symptom rather than fixing it; it is occasionally justified on a heavy modpack that stalls during world generation.