How do I upload my own world to my Minecraft Java server?

Stop your server, upload your world folder (the one with level.dat directly inside it) with your Game Panel’s file manager, and set level-name in server.properties to that folder’s exact name. Start the server again and you’re back in your own world.

Find the right folder

• A singleplayer world: close Minecraft first, then look in the saves folder inside .minecraft. That’s %APPDATA%\.minecraft on Windows, ~/Library/Application Support/minecraft on a Mac and ~/.minecraft on Linux. Each world has its own folder.
• A world from another host: it’s the folder named by level-name in that server’s server.properties, usually world.

Open the folder and check level.dat is right there. If you only see another folder, go into that one. A world folder tucked inside a second folder is a classic reason an upload seems not to work.

Upload it

Download a backup from your Game Panel first, then:

1. Stop your server from the Game Panel.
2. Don’t upload on top of the world the server made for itself, or the two will mix. Delete the server’s own world folder first (your backup has it), or give your folder a different name, such as survival.
3. Upload your world folder with your Game Panel’s file manager, next to server.properties.
4. Inside the uploaded folder, delete session.lock if there is one. It’s the lock file the game uses to claim a world it has open, and the server writes its own when it starts.
5. Open server.properties and set level-name to the folder’s name, character for character: level-name=survival.
6. Start your server from the Game Panel and join to check you’re where you left off.

Bringing the Nether and the End

Since Minecraft 26.1, vanilla and Paper both keep the whole world in one folder. The Overworld, Nether and End sit inside it under dimensions/minecraft/, and player data under players/. So a world from 26.1 or newer is one folder, even if it came from Paper.

Older worlds are laid out differently:

• Vanilla or singleplayer, before 26.1: the Nether and End are the DIM-1 and DIM1 folders inside the world folder, so they come along automatically.
• Paper, Spigot or Bukkit, before 26.1: the Nether and End are separate folders next to the world, world_nether and world_the_end. Upload them too, side by side with the world, and keep all three names exactly as they were on the old server.

PaperMC says a Spigot or CraftBukkit world can’t move straight onto Paper 26.1 or newer. It has to go through vanilla first, so check PaperMC’s migration guide before you try.

Worlds only go forwards

A world can move onto the same Minecraft version or a newer one, never an older one. The game warns that a world may become corrupted when you open it on a version older than the one it was saved in, and once a world has been upgraded to 26.1 there’s no going back.

So before you upload:

1. Find out which version the world was last played on.
2. Make sure your server runs that version or a newer one.
3. If the server’s newer, keep your backup somewhere safe. Once the world’s been upgraded, that backup is the only copy that opens on the old version.