Importing a Java World into the Seed Map

What the importer reads and what it changes

Every Java world folder has a level.dat, a small compressed NBT file with the world's settings. The importer reads four things from it. The seed, from Data → WorldGenSettings → seed on 1.16 and later, or Data → RandomSeed on older worlds. The spawn, from SpawnX and SpawnZ. The version name the world was last saved in. And the world's name, which it shows back to you so you know it read the right file.

It then switches the map to Java if it was on Bedrock, picks the version, sets the seed and centres the map on the spawn. The version choice is the newest entry in the version list that is not newer than the save: a world saved in 1.21.8 lands on the 1.21.6 – 1.21.8 band, a 26.3 world on 26.3, and a name like 1.20.1 Pre-Release 2 is read as 1.20. Large Biomes is never selected automatically, because level.dat's version name does not say which world type was used; if your world is Large Biomes, change that by hand afterwards.

All of this happens in your browser. The file is parsed by JavaScript on your machine and the seed goes to the same engine the map always uses. Nothing is uploaded, which is also why the import works offline once the page has loaded.

Where the file is

Inside the folder you want level.dat, not level.dat_old. The old file is the previous save and is usually fine too, but if the two disagree, the game trusts level.dat. If you would rather not dig for the file, zip the whole world folder with your system's compress command and drop the zip on the map instead; the importer finds level.dat inside it.

Step by step

1. Open the seed map. Next to the seed box there is a folder button; its tooltip reads Load from save (level.dat or world .zip).
2. Pick the level.dat, or the zipped world folder. The file picker accepts .dat and .zip.
3. Read the status line under the seed box. It says Loaded, then the world's name and the version it was saved in, for example Loaded My World (26.3).
4. Check the version box. If the world has crossed a major version since it was created, set the version that generated the area you want to look at.
5. The map is now centred on the world spawn. Zoom out and the structures around it are the ones in your game.

The three error messages

A fourth, generic Could not read that save appears if the browser cannot read the file at all, which in practice means a permissions problem or a file still being written by the game. Close the world first; Minecraft rewrites level.dat on every save.

Old worlds, mixed versions, snapshots

A world created years ago and still played has chunks from several versions. The importer can only tell you the last version the world was saved in, so after importing an old world, think about which area you want: the land around the original base follows the version the world was created in, and new chunks follow the current one. The troubleshooting guide has the full list of what moves between versions.

Worlds saved in snapshots import fine, with the version name rounded down to the nearest release. The generation itself may not match, since snapshots change weekly; the import gets you the seed and the spawn, and the version is your call.

Pre-1.16 worlds store the seed as RandomSeed and the importer reads it. Their terrain follows the old layer-based generator for 1.7 and later, which the engine supports; anything older than 1.7 is outside the version list.

Bedrock worlds

Bedrock's level.dat is a different file format, and .mcworld exports are zips of it, so neither can be imported. Read the seed from the world's settings instead: press the pencil icon next to the world on the Play screen, open Game, and copy the Seed field. Then choose Bedrock on the map and the version band that matches your game. The world seed guide covers each edition's settings in more detail.