How to switch or downgrade Minecraft versions safely

You may want an older version for a server, a mod or a favourite world. Going forward is usually fine. Going back is where worlds get damaged, so follow these steps.

The one rule#

Do not open a world in an older version than the one that last saved it. Newer versions change how worlds are stored, and an older version may fail to load it or corrupt it. Minecraft shows a warning in many cases, so read it and back out.

1. Back up first#

Close the game and back up your worlds. Copy the world folder somewhere safe before you try any version change.

2. Use a separate profile#

Create a new profile for the version you want, instead of changing your main one. In the FireClient launcher the Minecraft version and loader are set per profile, so keep one profile per version and loader.

3. Match Java to the version#

Different Minecraft versions need different Java versions. Minecraft 1.21.1 needs Java 21. Older versions may need an older Java. Check with the Java version checker and the Java 21 guide.

4. Match your mods#

Mods are built for one Minecraft version and one loader. When you switch versions, install the versions of the mods that match. See the mods guide and the loader comparison.

5. Test with a copy#

Make a copy of the world, put the copy in the older version's saves folder and try it there. Keep the original untouched.

Updating to a newer version#

Back up, make a new profile for the new version and open a copy of your world first. Check that your mods have updated before you move your main profile.

If something breaks#

Restore your backup and use the crash checklist. Ask in the FireClient Discord and never post account files or tokens.