Change the Minecraft server versionUpdating, rolling back and what happens to the world

Published on October 20, 2026

Back up first - always

A version change converts the world. When it starts under a newer version, Minecraft rewrites the world data into the new format - and this step is irreversible.

So before every change, back up the complete world folder and your configuration files. Backups are self-service with us via SFTP and WebFTP; how that works is described in Create backups.

If you skip this, you have no ticket back after a failed change - that is the most common avoidable total loss on Minecraft servers.

The right order

1. Check whether your extensions come along. Are the plugins and mods available for the target version? If not, the change is postponed.
2. Clarify the Java requirement. From 26.1, Java 25 is required; from 1.20.5 to 1.21.11, Java 21; for 1.18 to 1.20.4, Java 17 - see Change the Java version.
3. Stop the server and back up.
4. Switch the version and start the server.
5. Watch the console until "Done" appears - world conversion can take a while for large worlds.
6. Catch up on extensions and check them one by one.

The first point is the most important. A server running on the new version but without half of its plugins is worse for the community than one on the old version.

A special case is the jump from 1.21.x to the new numbering: since 2026, versions follow the pattern year.drop.hotfix, so 1.21.11 was followed by 26.1. That is not a fresh start but a perfectly normal update - though one that hits two points on the list at once: Java 25 is mandatory, and many plugins and mods need their own 26.x release.

Test on a copy first

The calmest change is one you have played through once beforehand. Because the conversion is irreversible, there is a single hard rule: never test on the original world, always on a copy.

1. Download the world folder via SFTP or WebFTP - that is your backup anyway.
2. Put the copy on a second server that already runs the target version.
3. Start it and go through the log instead of just waiting for "Done". Warnings about extensions show up there earlier than complaints in the chat.
4. Visit the places where an error would hurt: spawn, farms, redstone contraptions, large builds.
5. Catch up on plugins and mods one by one and check the console again after every restart.

Automatic farms and redstone constructions are particularly sensitive. They rely on behaviour that Mojang adjusts between versions - a farm that worked before can simply stand still after the change. A test shows this in ten minutes; without a test, the community notices on the first evening.

For a pure test run, a small server that can go again afterwards is enough. How to estimate the size is described in Plan your server size; you will find the prices for Minecraft on the product page.

What happens to plugins and mods

With modpacks: do not update the individual mods, but switch the pack as a whole to a newer release. Anything else ends in a server that no longer starts - see Install a modpack.

Downgrade: why it is tricky

The way back is far more difficult than the way forward. Minecraft can convert world data upwards, but not downwards.

• A world started under 1.21 can not be played on reliably under 1.20.
• New blocks and items from the higher version do not exist in the older one - at best, they disappear; at worst, they damage chunks.
• The only reliable way back is the backup from before the change.

This is exactly why backing up comes first in this guide. If you are unsure whether the new version fits: back up first, then test, and if necessary restore the backup.

After the change: what players see

A Minecraft client only connects to a server of the same version. After the change, anyone who still has the old profile in their launcher gets a clear message in the server list: Outdated client means the player has to switch their launcher profile to the new version. Outdated server, conversely, means the player is already further ahead than you.

So announce the change and name the target version explicitly - the address made of IP and port stays unchanged; only the version in the launcher changes. How players switch their profile is described in Join a server; if an error remains afterwards, Fix connection errors helps.

Check three things directly after the first successful start:

• Whether the world's datapacks are still listed as enabled - the server reports a mismatched pack_format number at startup.
• Whether newly generated terrain joins the old terrain cleanly. If a version changes world generation, a visible edge appears at the border - and it does not go away on its own.
• Whether the values in server.properties are still there. New versions add extra keys to the file; existing settings are kept.

Snapshots and pre-releases

Snapshots are pre-releases with which Mojang tests upcoming features. They are unsuitable for a production server:

• World formats change between snapshots - a world can become unusable from one snapshot to the next.
• There are practically no plugins and mods for them.
• Players need exactly the same snapshot in their launcher.

If you want to try out new things, it is better to use a second server or a separate world for that - and leave the community world on a stable version.

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