What Java version do I need (17 / 21) and how do I set it?

Every Minecraft version expects a particular Java version, and a mismatch is one of the most common reasons a server won't start. The good news is you can set the Java version yourself on the Settings page.

Which Java version you need

• Java 8 for older versions (1.16 and below).
• Java 17 for roughly 1.17–1.20.4.
• Java 21 for 1.20.5+ and 1.21+.

Newer Minecraft needs newer Java, so match the two before you start.

How to set it

1. Open the Settings page.
2. Use the Docker image / Java version selector to pick the right version for your Minecraft version.
3. Save and start the server.

Warning: A wrong Java version is a common "won't start" cause — the Console will show something like "unsupported class version" when Java and Minecraft don't match.

Frequently asked questions

How do I know which Java my version needs? As a guide: Java 8 for 1.16 and below, Java 17 for 1.17–1.20.4, and Java 21 for 1.20.5 and newer.

Where do I change it? On the Settings page, via the Docker image / Java version selector. If the image is admin-locked, open a ticket.