Which Java version does your Minecraft server need?

Newer Java versions can often run a slightly older Minecraft, but the other way round never works. Old modded versions are the exception: Forge on 1.12.2 and 1.7.10 wants exactly Java 8.

Mojang raises the Java requirement every few years, always together with a big update:

Before 1.17, every version ran on Java 8 for years. That is why so many old servers and packs still need it, and why a server that skips several Minecraft versions at once often needs a new Java as well.

1. Open Settings.
2. Change the Minecraft version. The Java version follows automatically.
3. Only if you need something else, pick a Java version by hand below it, for example Java 8 for an old modpack.
4. Restart the server.

If you picked a Java version by hand and later change the Minecraft version, check the Java setting again. The automatic choice is almost always right.

When Java is too old, the console shows an error like this:

java.lang.UnsupportedClassVersionError: ... has been compiled by a more recent version of the Java Runtime (class file version 69.0), this version of the Java Runtime only recognizes class file versions up to 65.0

The two numbers tell you what was needed and what is installed. Translate them with this table:

So the example needs Java 25 and found Java 21. Raise the Java version in Settings, or check that the Minecraft version there matches the server files.

Not every error with the word java in it is about the Java version. These are the ones we see most:

When the server stops before the console shows anything useful, work through the other causes in order with Minecraft server won't start.

A plugin or mod built for a newer Java than your server runs gives the same class version error, but names that plugin. Either update Java together with Minecraft, or use an older build of that plugin that fits your version.

Old modpacks on Java 8 sometimes need extra startup flags that newer Java versions do not understand. If a pack's server files include their own start settings, use the Java version the pack's makers recommend.

For the normal game, the Minecraft Launcher brings its own Java, so players do nothing. Third party launchers such as Prism Launcher can download the right Java per profile; when a modpack crashes at launch on a player's computer, a wrong Java in that launcher profile is a common cause.

A Bedrock server does not use Java at all. The official Bedrock server software from Mojang is a program of its own, so there is no Java setting to think about.

Crossplay changes nothing here: underneath it runs Paper with Geyser, so the table above applies as it is. Geyser itself needs a recent Java, which is one more reason to keep a crossplay server on a current Minecraft version. Java and Bedrock crossplay explains the rest of that setup.