How to Fix "Unsupported Class Version" Errors in Minecraft Servers

The most common reason self-hosted Minecraft servers fail to start, and how to fix it for good.

If your Minecraft server is crashing with an error like:

Exception in thread "main" java.lang.UnsupportedClassVersionError

You're running the wrong version of Java for your Minecraft version. This is the most common reason self-hosted servers fail to start.

Why this happens

Minecraft's server software is compiled for a specific version of Java. When the Java installed on your machine doesn't match what the server expects, you get this error.

Minecraft Version	Required Java
1.8 to 1.16	Java 8
1.17	Java 16 or newer
1.18 to 1.20.4	Java 17 or newer
1.20.5 and newer (1.21+)	Java 21 or newer

Most players have one version of Java installed. If you update Minecraft but not Java, the server breaks.

The manual fix

1. Find out which Minecraft version your server runs
2. Look up the required Java version in the table above
3. Go to Adoptium (adoptium.net) and download the correct version
4. Install it without overwriting your existing Java (if you use it for other things)
5. Point your server launcher at the new Java executable manually

This works, but you'll need to repeat it every time you update Minecraft.

The automatic fix

You never touch Java again.

The Lite version is completely free and includes Auto Java Detection with no time limit on this feature.