Version upgrades

Server Settings has an Upgrade Minecraft Version card (Coalstack Plus, Java servers). It moves a server to a newer Minecraft version in one guided flow: a check that changes nothing, a backup, the upgrade itself, and an undo until you decide to keep it. Only newer versions are offered, because Minecraft can't open a world that a newer version has saved.

What it can upgrade

Vanilla, Paper, Fabric, Quilt, Forge and NeoForge servers that Coalstack can recognise. Purpur, Spigot, a custom server jar and Bedrock servers aren't supported yet, and the card says why. The server has to be stopped.

The check

Pick a version and Coalstack looks up every jar in mods/ (or plugins/ on Paper) on Modrinth by its contents, so a renamed file still counts. Each one ends up in one of four groups:

• Works as it is: the installed build already lists the new version.
• Will be updated: Modrinth has a build for the new version. You can keep the current file instead.
• No version for it yet: disabled by default (moved aside, not deleted). You can keep it, but it may stop the server from starting.
• Not on Modrinth: kept by default, because Coalstack can't tell whether it works. You can disable it.

The upgrade

Coalstack backs up the world first (a restore-tested snapshot; if that fails nothing is changed), downloads the updates and checks each against the checksum Modrinth publishes, sets the old server files aside, installs the new server and applies your choices. If any step fails the file changes are undone for you. The server is left stopped: start it to finish.

Keep or undo

Until you press Keep the upgrade, the card offers Undo. Undo puts the old server files and mods back and restores the world from just before the upgrade, so anything players built since is lost. Keep clears the undo files and leaves the backup among your snapshots. The undo files live in the server's .coalstack-upgrade folder.

Limits

An updated mod can need a new library mod that wasn't installed before. Coalstack doesn't add those during the upgrade; if the server then fails to start, Auto-fix downloads what is missing. Jars outside mods/ and plugins/, datapacks and resource packs aren't checked.