Which Java Version Does My Minecraft Server Need?

Minecraft 26.1 and newer need Java 25, 1.20.5–1.21.11 need Java 21, and 1.18–1.20.4 need Java 17. Change it under Startup > Docker Image and restart.

A newer Java usually runs older Vanilla and Paper versions fine. Modded servers are stricter: Forge 1.16.5 and older only run reliably on Java 8.

Change it

1. In the Crunchy.Host panel, open Startup.
2. Under Docker Image, pick the image with the Java version you need.
3. Restart the server. The first lines of the log show which Java is in use.

If you can't change the image, check you're on Startup and not Settings. Subusers need the owner to grant that permission. If the version you need isn't listed, open a ticket.

Errors from the wrong version

Java too old:

java.lang.UnsupportedClassVersionError: ... (class file version 65.0), this version of the Java Runtime only recognizes class file versions up to 61.0

The first number is what the server needs: 52 is Java 8, 61 is Java 17, 65 is Java 21, 69 is Java 25.

Java too new for an old Forge server usually shows AppClassLoader cannot be cast to class java.net.URLClassLoader. Switch to Java 8.