Updating your server to a new Minecraft version, safely

A new Minecraft release brings new blocks, mobs and biomes, and players want them on day one. But updating a server is a one-way door: once a world has been opened on a newer version, it cannot be safely opened on the older one again. Doing it in the right order avoids a broken server and a group of unhappy friends.

Should you update yet?

• Vanilla — update whenever you like; a new release is ready on day one.
• Paper and Purpur — new builds usually appear within days of a release, marked experimental at first. Waiting until the first stable build avoids early bugs.
• Plugins — check each one has a version for the new release. Big plugins such as protection, permissions and logging tools often take days or weeks.
• Modded servers — every mod must be updated by its author, and modpacks update only when the pack does. Large packs often stay on one Minecraft version for years. If you run a modpack, you update when the pack does — not before.

If one plugin your server depends on is not ready, wait. A server missing its land-claims plugin for a week is worse than a server without the new mobs.

Before you update

1. Take a backup and keep it until you are sure the update is fine. See How backups work.
2. Download the new version of every plugin or mod, so the switch is quick.
3. Tell your players. Everyone needs to switch their game to the new version too — Java Edition only connects to a server on the same version.

The update itself

1. Stop the server.
2. Change the version — on Cobbly, on the Software tab. The right Java version is chosen for you; see Which Java version does my Minecraft server need?.
3. Replace each plugin or mod jar with the version for the new release, and delete the old jars.
4. Start and watch the console. The first start takes longer — the world’s data is being converted.
5. Join, look around your main areas, open some chests, and check the plugins respond.

What happens to the world

The world is not converted all at once. Minecraft upgrades each chunk the first time it is loaded on the new version, and saves it in the new format. Builds, chests and items all carry over.

Terrain that already exists stays exactly as it was. New features — new biomes, new structures, new cave shapes — only appear in chunks that have never been generated. To find them, players need to explore beyond where anyone has been. On a server with a world border, you may need to widen it.

You cannot downgrade

Opening a world on an older version than it was last played on is not supported. Blocks and items that do not exist in the old version are lost, and the world can fail to load or become corrupted. If an update goes badly, the way back is your backup from before the update, restored on the old version — not changing the version number back.

Letting players on other versions join

On Paper, the ViaVersion plugin lets players on newer clients join an older server, and ViaBackwards lets players on older clients join a newer one. They are useful while everyone catches up after an update. They are not perfect — new blocks show up as substitutes for players on old versions — and they do not work on modded servers.

If the server will not start after updating

Almost always, it is a plugin or mod that was not updated. The console names it. Remove that jar, start again, and add the updated version when it exists. Why won’t my Minecraft server start? shows how to read the error.