Minecraft Chunk Format

Java Edition Save Format

A level is the game's persistent representation of a world. Java Edition only; Bedrock has its own save format. This page describes the current (26.1+) structure; see "Java Edition save format/1.21.11" for the pre-26.1 layout.

Save Locations

• Client: every save is a directory under .minecraft/saves/; a directory counts as a save only if it contains level.dat or level.dat_old.
• Server: root = u/w where u is the --universe launch argument (default ., the working directory) and w is the --world argument or level-name from server.properties.

Save Structure

Bold = always present (after initialization with at least one player joining); backups (level.dat_old, session.lock variants) not shown.

Dimension-Independent Files (save root)

• icon.png — save icon.
• level.dat — base save data.
• resourcepacks/ — world-specific resource pack directory; resources.zip — world-specific resource pack.
• session.lock — session lock file.
• players/ — player data:
  • advancements/<player UUID>.json — advancements.
  • data/<player UUID>.dat — player data.
  • stats/<player UUID>.json — statistics.
• data/ — save data:
  • minecraft/ — data in the minecraft namespace:
    • maps/ — last_id.dat (map counter) + <map ID>.dat (map data).
    • command_storage.dat — command storage.
    • custom_boss_events.dat — custom boss bars.
    • game_rules.dat — game rules.
    • random_sequences.dat — random sequences.
    • scheduled_events.dat — scheduled events (planned ticks).
    • scoreboard.dat — scoreboard.
    • stopwatches.dat — stopwatches.
    • wandering_trader.dat — wandering trader data.
    • weather.dat — weather data.
    • world_clocks.dat — world clocks.
    • world_gen_settings.dat — world generation settings.
  • <namespace>/ — other namespaces (currently only command storage uses non-minecraft namespaces).
• datapacks/ — world-specific data packs.
• generated/<namespace>/structure/<name>.nbt — generated structures (structure block exports).

Dimension Directories

Relative to the save root: Overworld = the save root itself, Nether = DIM-1, End = DIM1 (custom dimensions use their own folders). Each dimension directory:

• data/minecraft/ — dimension data: chunk_tickets.dat (chunk tickets), raids.dat, ender_dragon_fight.dat (End only, or dimensions with a dragon fight; not auto-created elsewhere), world_border.dat.
• entities/ — r.<region X>.<region Z>.mca region entity files (+ c.<chunk X>.<chunk Z>.mcc region extra files).
• poi/ — point-of-interest data: r.<region X>.<region Z>.mca (+ .mcc extra files).
• region/ — chunk data: r.<region X>.<region Z>.mca (+ .mcc extra files).

Upgraded Saves

Older saves may additionally contain level.dat_mcr and worldgen_settings_export.json (world generation settings export).

Storage History

• Alpha: each chunk stored in its own file.
• Beta 1.3: MCRegion format.
• 12w07a: Anvil file format — regions of 32×32 chunks in .mca files, still used today (.mcc extra files added later for region overflow data).