Turn on experimental features on your server

Java Edition experiments are built-in data packs for features Mojang is still testing. On a server they are not a button in the panel. You name them in server.properties before the server creates a world. The experiments that shipped with Minecraft 1.21 are now ordinary gameplay, so this guide covers the ones that are still experimental today.

Checked against the Minecraft 26.3 server, October 2026.

What you can turn on

The 26.3 server jar contains three experimental data packs:

The older Java experiments, including Update 1.21, Bundles and the Locator Bar, have been removed from the experiments list and are part of normal gameplay. The panel's JAR Manager offers release versions only, so features that exist only in a snapshot are not available.

Turn one on for a new world

The initial-enabled-packs line only applies when a world is created. For a world that already exists you need a new one.

1. Open the Backups tab and click Create backup.

2. On the Console tab, click Stop and wait for Offline.

3. Open the Config Editor, change World folder in the World section to a new name such as experiment, and click Save changes. Changing it starts a new world and leaves the old folder on disk.

4. Open File Manager, select server.properties and click Edit. The Config Editor does not list this setting, and it leaves lines it does not know untouched.

5. Find initial-enabled-packs=vanilla. Add the pack after it, separated by a comma and with no spaces:

   initial-enabled-packs=vanilla,minecart_improvements

   Keep vanilla in the list. To turn on several, add each ID after another comma.

6. Click Save, then press Start on the Console tab.

The first start generates the new world with the pack on. Paper's own source reads this same server.properties line, and Purpur is built on Paper without changing it, so both read it too.

Check it worked

Once the server is running, send this on the Console tab:

datapack list

The pack you added appears among the enabled data packs, tagged (feature). On Paper the reply reads:

There are 3 data pack(s) enabled: [vanilla (built-in)], [minecart_improvements (feature)], [paper (built-in)]

The paper (built-in) entry is Paper's own data pack.

Existing worlds and the Datapacks tab

The Datapacks tab installs data packs from Modrinth into your world. It is not where Mojang's built-in experiments are switched on.

The Minecraft Wiki says an existing world can be given a feature by editing level.dat in an NBT editor, but it marks the details as incomplete. We do not recommend it. If you want to try, back up first and see Edit level.dat and player data with an NBT editor.

If it does not work

• The pack is not in datapack list. The world already existed when you edited the file. Use a new World folder name so the server creates a fresh world.
• You changed your mind. Restore the backup from step 1 to go back to the world you had before. See Reset your world and start fresh if you want a clean start.
• You want another experiment. The IDs in the table match the 26.3 server jar. Later versions can add or remove experiments, so check the Minecraft Wiki's Experiments page.