Understanding Your World's File Structure

The World Folder at a Glance

The server directory holds the server jar, server.properties, and a subfolder for the world, named by the level-name setting, which defaults to world. Everything the game needs to render and save your game sits inside it. Browse it from the portal file manager or over SFTP and you will see the same layout on nearly every server.

A typical fresh world folder:
world/
├── region/
│   ├── r.0.0.mca
│   ├── r.0.1.mca
│   └── r.-1.0.mca
├── DIM-1/
├── DIM1/
├── playerdata/
├── stats/
├── advancements/
├── level.dat
├── level.dat_old
└── session.lock

Region Files and Chunk Coordinates

Terrain is stored in region files, each covering a 32 by 32 block of chunks, 512 by 512 blocks, and named r.<regionX>.<regionZ>.mca. The name comes from block coordinates divided by 512: r.0.0.mca spans x 0 to 511 and z 0 to 511, while r.0.-1.mca reaches into negative z. To find a region from block coordinates, divide by 512; from chunk coordinates, divide by 32. Unexplored terrain simply has no region file yet.

• r.0.0.mca stores all chunks containing blocks x 0 to 511 and z 0 to 511.
• r.-1.0.mca and r.0.-1.mca hold the neighbouring negative-coordinate strips.
• A missing region file is normal; the area generates on first visit.
• Region files are compressed, so active regions run to megabytes while empty ones stay tiny.

Nether, End, and Custom Dimensions

Each dimension has its own folder with region files and level.dat. The Nether lives in DIM-1 and the End in DIM1, names taken from dimension ids -1 and 1. With a custom level-name, Minecraft appends _nether and _the_end, so a world called overworld becomes overworld_nether and overworld_the_end. The Nether is scaled one to eight, so its region grid covers a smaller physical footprint. Deleting a dimension folder resets that dimension, so back it up before editing.

• DIM-1 is the Nether; DIM1 is the End.
• level-name=overworld produces overworld, overworld_nether, and overworld_the_end.
• Nether scaling makes its region grid one-eighth the physical size of the overworld's.

Player Data, Stats, and Advancements

playerdata holds one <uuid>.dat per player with inventory, equipment, position, and health, keyed by Mojang UUID rather than username, so a name change never orphans the file. stats records blocks broken, mobs killed, and distance travelled; advancements tracks achievements on Java. The game writes these on logout and on scheduled autosaves. Copying a player's .dat moves their inventory; deleting one resets their progress.

• Run /save-all before inspecting or copying player files.
• A changed hotbar usually means playerdata was overwritten by an old backup.
• Stats and advancements are per-server unless copied across too.

level.dat, session.lock, and the Configs Around It

level.dat is one compressed NBT file with the seed, time, weather, spawn, gamerules, and persistent data; level.dat_old is the rotated safety copy from the previous save. session.lock marks the folder as open, which is why the portal pauses the server for backups. Outside the folder, server.properties sets level-name, seed, gamemode, and view distance, while ops.json, whitelist.json, and banned-players.json handle access, and logs keeps console history.

• The level-name key decides which folder is the playable world.
• Edit ops.json and whitelist.json through the op and whitelist commands, not by hand.
• Back up the whole folder; region files alone lose playerdata, stats, and the seed.