A Minecraft plugin or mod needs a newer Java

Every piece of a Minecraft Java server is built for a minimum Java version: the server software, each plugin and each mod. When the server software or a mod needs a newer Java than your server runs, the server stops at start. A plugin that needs a newer Java does not load, and the rest of the server runs without it. Switch the server to the Java it asks for, or install a version of the plugin or mod made for the Java you have.

What you see

In the Console, one of these lines:

• UnsupportedClassVersionError with has been compiled by a more recent version of the Java Runtime (class file version and a number;
• requires running the server with Java or requires at least Java and a number;
• for a Fabric, Forge or NeoForge mod, a line that names java as a dependency the mod needs.

On Overview, and above the console, the Why your server stopped box names it:

The numbers are examples: the box uses the ones from your server. When the line came from the console rather than a crash report, Switch to Java becomes Open launch details, so you pick the Java yourself.

The box only reads what the server printed after it last finished starting. A plugin that failed to load during a start that otherwise worked is therefore not in the box: look for its line in the Console.

On most server types Overview also shows a banner, This server needs a different Java version, with a Switch version button, when the error comes in while you have Overview open.

Read the class file number

A class file version is a Java version plus 44. For example 61 is Java 17, 65 is Java 21 and 69 is Java 25. The panel does this sum for you in the box above.

Fix it in one click

1. Open your server in the panel, on Overview or Console.
2. In Why your server stopped, click Switch to Java and the number. The box says The server now uses Java and the number, Start it again.
3. Click Start.

From the banner instead: click Switch version, choose the Java in the Choose a Java version window, and click Switch and start.

Fix it by hand

1. Open Settings and click Launch Details, or click Open launch details in the box.
2. Under Docker image, choose the newer Java in the list. It is saved as soon as you choose it. More detail: How to change the Java version of your Minecraft server.
3. Start the server.

When the panel will not switch

Some server software does not start on a Java that is too new for it, and the panel refuses that choice. For example the panel says This software on Minecraft and the version does not start on Java and the number. Then the box does not offer Switch to Java. It says one of these instead:

• This server software cannot run on Java and the number. Install a version of the plugin that works on the Java you have.
• A plugin or mod was built for Java and a number which this server software cannot run. Remove it, or install a version that works on your Java. Open in Files takes you to it.
• This Minecraft version needs Java and a number which this server cannot switch to here. Contact support. Open a ticket.

To find another build of a plugin or mod, click Find and its name to open Modding, search the name, and choose a version made for your Minecraft and Java. See How to install plugins on Paper, Spigot and Purpur and How to install mods on Forge, Fabric and NeoForge.

Good to know

• Who can switch: your role needs the permission to change the server's Java image. Ask the server owner otherwise.
• Pick the Java the message names, not the newest one. Older server software may not start on a much newer Java, and the panel refuses those choices.
• More causes, one guide each: How to see why your Minecraft server stopped.