Java Edition level format

From Minecraft Wiki

(Redirected from Session.lock)

This feature is exclusive to Java Edition.

Each level (world) has its own folder. A level folder is often identified by having a level.dat file, along with other subfolders to store the maps and regions of the level.

Directory structure

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Current

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This is the directory structure of the .minecraft/saves folder, where the game saves the entire world data:

👁 File directory.png: Sprite image for directory in Minecraft
: A world directory.
- 👁 File file.png: Sprite image for file in Minecraft
  level.dat: Stores global information about the level. See below.
- 👁 File file.png: Sprite image for file in Minecraft
  level.dat_new: Program writes new global information about the level, and after that file is renamed to level.dat.
- 👁 File file.png: Sprite image for file in Minecraft
  level.dat_old: A backup of the previous level.dat file.
- 👁 File file.png: Sprite image for file in Minecraft
  session.lock: Used to give write access to the last program to modify this file. See below.
  - 👁 File file.png: Sprite image for file in Minecraft
    <uuid>.dat: A data file of the player. See Player.dat format.
  - 👁 File file.png: Sprite image for file in Minecraft
    <uuid>.json: A data file of the player. See Statistics storage format.
  - 👁 File file.png: Sprite image for file in Minecraft
    <uuid>.json: A data file of the player. See Advancement storage format.
- 👁 File directory.png: Sprite image for directory in Minecraft
  data: Miscellaneous data of the world.
  - 👁 File directory.png: Sprite image for directory in Minecraft
    minecraft: Vanilla namespace for Miscellaneous data of the world.
    - 👁 File file.png: Sprite image for file in Minecraft
      game_rules.dat: Gamerules of the world.
    - 👁 File file.png: Sprite image for file in Minecraft
      random_sequences.dat: Stores random number sequences for loot tables or the /random command. See Random sequence format.
    - 👁 File file.png: Sprite image for file in Minecraft
      scoreboard.dat: Stores scoreboard data, such as objectives' definition, entities' scores, teams, and display slots of objectives. See Scoreboard § NBT format.
    - 👁 File file.png: Sprite image for file in Minecraft
      stopwatches.dat: Stores Stopwatch data.
    - 👁 File file.png: Sprite image for file in Minecraft
      wandering_trader.dat: Stores Wandering Trader data.
    - 👁 File file.png: Sprite image for file in Minecraft
      world_clocks.dat: Stores World Clock data.
    - 👁 File file.png: Sprite image for file in Minecraft
      world_gen_settings.dat: Stores World Generation Settings data.
    - 👁 File file.png: Sprite image for file in Minecraft
      scheduled_events.dat: Stores Scheduled Events data.
    - 👁 File file.png: Sprite image for file in Minecraft
      custom_boss_events.dat: Stores Boss Events data.
    - 👁 File file.png: Sprite image for file in Minecraft
      weather.dat: Stores Weather related data.
- 👁 File directory.png: Sprite image for directory in Minecraft
  datapacks: Stores the world's data packs.
  - 👁 File archive.png: Sprite image for archive in Minecraft
    👁 File directory.png: Sprite image for directory in Minecraft
    <datapack>: A data pack.
- 👁 File directory.png: Sprite image for directory in Minecraft
  dimensions: Contains region files of dimensions, added by vanilla, data packs or mods.
  - 👁 File directory.png: Sprite image for directory in Minecraft
    <namespace>: Namespace of the defined dimension.
    - 👁 File directory.png: Sprite image for directory in Minecraft
      <path>: Path of the defined dimension.
      - 👁 File directory.png: Sprite image for directory in Minecraft
        data: Miscellaneous data of the custom dimension.
        👁 File file.png: Sprite image for file in Minecraft
        raids.dat: Stores information about the ongoing raids in this dimension.
      - 👁 File directory.png: Sprite image for directory in Minecraft
        region: See above.
      - 👁 File directory.png: Sprite image for directory in Minecraft
        entities: See above.
      - 👁 File directory.png: Sprite image for directory in Minecraft
        poi: See above.
  - 👁 File directory.png: Sprite image for directory in Minecraft
    minecraft: Namespace of the vanilla dimension.
    - 👁 File directory.png: Sprite image for directory in Minecraft
      overworld: Path of the Overworld dimension.
      - 👁 File directory.png: Sprite image for directory in Minecraft
        data: Contains data of the Overworld.
        👁 File directory.png: Sprite image for directory in Minecraft
        <namespace>: Namespace for the Overworld data.
        
        👁 File directory.png: Sprite image for directory in Minecraft
        minecraft: Vanilla Namespace for the Overworld data.
        👁 File file.png: Sprite image for file in Minecraft
        raids.dat: Stores information about the ongoing raids in Overworld. See raids.dat format.
        
        👁 File file.png: Sprite image for file in Minecraft
        world_border.dat: Stores information about the World Border.
        
        👁 File file.png: Sprite image for file in Minecraft
        chunk_tickets.dat: /forceload.
      - 👁 File directory.png: Sprite image for directory in Minecraft
        entities:
        👁 File directory.png: Sprite image for directory in Minecraft
        entities: Contains entity files for the Overworld. These used to be part of region.
      - 👁 File directory.png: Sprite image for directory in Minecraft
        poi:
        👁 File directory.png: Sprite image for directory in Minecraft
        poi: Villager identified beds, job sites, and bells in the Overworld. Nether portals, bee nests, bee hives, and lodestones also use this.
      - 👁 File directory.png: Sprite image for directory in Minecraft
        region:
        👁 File file.png: Sprite image for file in Minecraft
        r.<x>.<y>.mca: A region file. See Anvil file format.
    - 👁 File directory.png: Sprite image for directory in Minecraft
      the_end: Path of the End dimension.
    - 👁 File directory.png: Sprite image for directory in Minecraft
      the_nether: Path of the End dimension.
- 👁 File directory.png: Sprite image for directory in Minecraft
  resourcepacks: Contains resourcepacks of the world.
  - 👁 File archive.png: Sprite image for archive in Minecraft
    resources.zip: A resource pack applied when the world loads in.

Deprecated

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👁 File directory.png: Sprite image for directory in Minecraft
: A world directory.
- 👁 File file.png: Sprite image for file in Minecraft
  level.dat_mcr: A backup of the level.dat file before conversion from MCRegion to Anvil.
- 👁 File directory.png: Sprite image for directory in Minecraft
  players: Stores the individual states of the players that have played on this level, for versions before 1.7.6.
  - 👁 File file.png: Sprite image for file in Minecraft
    <player>.dat: A data file of the player. See Player.dat format.
- 👁 File directory.png: Sprite image for directory in Minecraft
  data: Miscellaneous data of the world.
  - 👁 File file.png: Sprite image for file in Minecraft
    villages.dat: Stores information about the villages in the world. The "nether" and "end" files have been added in 1.8. Replaced by point of interest region files in 1.14.
  - 👁 File file.png: Sprite image for file in Minecraft
    villages_nether.dat: See above.
  - 👁 File file.png: Sprite image for file in Minecraft
    villages_end.dat: See above.
- 👁 File directory.png: Sprite image for directory in Minecraft
  region: Backups of the region files before conversion from MCRegion to Anvil.
  - 👁 File file.png: Sprite image for file in Minecraft
    r.<#>.<#>.mcr: A region file. See Region file format.
- 👁 File directory.png: Sprite image for directory in Minecraft
  DIM-1: See above.
  - 👁 File file.png: Sprite image for file in Minecraft
    r.<#>.<#>.mcr: A region file. See Region file format.
- 👁 File directory.png: Sprite image for directory in Minecraft
  DIM1: See above.
  - 👁 File file.png: Sprite image for file in Minecraft
    r.<#>.<#>.mcr: A region file. See Region file format.
- 👁 File directory.png: Sprite image for directory in Minecraft
  <#>
  - 👁 File directory.png: Sprite image for directory in Minecraft
    <#>
    - 👁 File file.png: Sprite image for file in Minecraft
      c.<#>.<#>.dat: Backups of the chunk files before conversion from the Alpha level format to MCRegion. See Alpha level format.

level.dat format

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The level.dat file contains global information about the world such as the time of day, the singleplayer player, the level generator used, and the seed. When a world is loaded, the current level.dat is backed up to level.dat_old. It is an NBT file with this structure:

[NBT Compound / JSON Object] The root tag.
- [NBT Compound / JSON Object] Data: This tag contains all the level data.
  - [Boolean] allowCommands: 1 or 0 (true/false) - true if cheats are enabled.
  - [NBT Compound / JSON Object] DataPacks: Options for data packs.
    - [NBT List / JSON Array] Disabled: List of disabled data packs.
      - [String]: A single data pack.
    - [NBT List / JSON Array] Enabled: List of enabled data packs. By default, this is populated with a single string "vanilla".
      - [String]: A single data pack.
  - [Int] DataVersion: An integer displaying the data version.
  - [NBT Compound / JSON Object] difficulty_settings: This tag contains all difficulty settings.
    - [String] difficulty: The difficulty of the world. e.g. "normal".
    - [Boolean] hardcore: 1 or 0 (true/false) - If true, the player respawns in Spectator on death in singleplayer. Affects all four game modes.
    - [Boolean] locked: 1 or 0 (true/false) - If true, the player cannot change the difficulty of the world.
  - [NBT List / JSON Array] enabled_features: List of experimental features enabled for this world. Doesn't appear if there are no experimental features enabled.
    - [String]: A single experimental feature.
  - [Int] GameType: The default game mode for the singleplayer player when they initially spawn. 0 is Survival, 1 is Creative, 2 is Adventure, 3 is Spectator. Note: singleplayer worlds do not use this field to save which game mode the player is currently in.
  - [Boolean] initialized: 1 or 0 (true/false) - Normally true after a world has been initialized properly after creation. If the initial simulation was canceled somehow, this can be false and the world is re-initialized on next load.
  - [Long] LastPlayed: The Unix time in milliseconds when the level was last loaded.
  - [String] LevelName: The name of the level.
  - [Int Array] single_player_uuid: UUID of the player in singleplayer
  - [NBT List / JSON Array] ServerBrands: List of brands of the level.
    - [String]: A single server brand. e.g. "vanilla".
  - [NBT Compound / JSON Object] spawn: The world spawn data.
    - [String] dimension: The spawn dimension, as three integers
    - [Int] pitch: The pitch.
    - [Int] yaw: The yaw.
    - [Int Array] pos: The spawn position.
  - [Long] Time: The number of ticks since the start of the level.
  - [Int] version: File format version of level.dat. Values 19132 or 19133 represent Region and Anvil respectively.
  - [NBT Compound / JSON Object] Version: Information about the Minecraft version the world was saved in.
    - [Int] Id: An integer displaying the data version.
    - [String] Name: The version name as a string, e.g. "15w32b".
    - [String] Series: Developing series. In 1.18 experimental snapshots, it was set to "ccpreview". In others, set to "main".
    - [Boolean] Snapshot: 1 or 0 (true/false) – Whether the version is a snapshot or not.
  - [Boolean] WasModded: 1 or 0 (true/false) - true if the world was opened in a modified version.

generatorOptions tag format

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The [NBT Compound / JSON Object] generatorOptions tag format varies depending on the generator name. It affects only the Overworld dimension. This applies to 1.15 and below.

This is the format for the Buffet world type:

[NBT Compound / JSON Object] generatorOptions:
- [NBT Compound / JSON Object] biome_source:
  - [NBT Compound / JSON Object] options: Ignored if the biome source ID is minecraft:vanilla_layered.
    - [NBT List / JSON Array] biomes:
      - [String]: A biome ID. If this or the biome source ID is omitted or invalid, the code assumes minecraft:ocean.
    - [Byte] size: The size of the biomes. Only used when the biome source ID is minecraft:checkerboard. The biome squares have sides of 2^<size> (which can be < 1) chunks. If no value is entered, the code assumes 2.
  - [String] type: An applicable biome source ID. It determines how the biomes are distributed. Cannot be selected in-game and defaults to minecraft:fixed for unmodified worlds.
- [NBT Compound / JSON Object] chunk_generator:
  - [NBT Compound / JSON Object] options:
    - [String] default_block: A block ID, by default minecraft:stone.
    - [String] default_fluid: A fluid ID, by default minecraft:water.
  - [String] type: An applicable chunk generator ID. It determines the overall structure of the dimension. If this is omitted or invalid, the code assumes minecraft:surface.

This is the format for the Superflat world type:

[NBT Compound / JSON Object] generatorOptions:
- [NBT Compound / JSON Object] structures:
  - [NBT Compound / JSON Object] <structure name>: An empty compound named as the structure, for example decoration. If parameters are set, for example village(distance=9 size=1), then the compound contains this information.
    - [String] <parameter name>: The parameter value is a number represented by a string.
- [NBT List / JSON Array] layers:
  - [NBT Compound / JSON Object]: A layer.
    - [String] block: The block ID.
    - [Int] height: The height of the layer, used in worlds created before 1.13-pre5.
    - [Byte] height: The height of the layer, used in worlds created since 1.13-pre5, if it's < 128 blocks.
    - [Short] height: The height of the layer, used in worlds created since 1.13-pre5, if it's >= 128 blocks.
- [String] biome: The biome ID.
- [String] flat_world_options: The unescaped "generator-settings" string. Created only if the world was generated through a server. Until snapshot 20w11a, it is not parsed by the game due to MC-134900, thus the above compounds won't be created, making "generator-settings" ineffective.

This is the format for the Old Customized world type that existed before 18w06a:

[String] generatorOptions: Controls options for the world generator. Used only if the world type is Superflat or Customized. The format for Superflat is a comma separated list of block IDs from the bottom of the map up, and each block ID may optionally be preceded by the number of layers and an "*" ("x" before 1.8). Damage values are not supported.^[1] See detailed format for Superflat world type: before 1.8 and in 1.8-1.12. Refer also to Superflat#History that shows how the format has been changing over time. The format for Customized world type is an extremely long String which consists of name:value pairs resembling JSON (as shown in Old_Customized#Presets).

session.lock format

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This file contains a single character U+2603 ☃ SNOWMAN encoded (E2 98 83) in UTF8.

The process goes something like this:

Program opens session.lock.
Program writes a single character ☃ (\u2603) to session.lock.
Program tries to acquire a lock on a session.lock.
If the lock on a session.lock fails, program aborts and gives up its lock on the level.

Minecraft can sometimes try to hold the lock on a level even after the player has started playing a different level, and this can cause strange behavior. It is recommended to ensure that Minecraft is closed before trying to acquire a lock on a level.

Before 1.16, the lock contained a big endian 64-bit integer timestamp of when the level was last accessed since the epoch. The program, instead of writing a snowman and acquiring a lock, would monitor the file for changes, and would abort if changed.

`poi` format

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Files in the poi folder use similar structure to region Anvil files (hence the mca extension), but the NBT content is different.

[NBT Compound / JSON Object] The root tag.
- [NBT Compound / JSON Object] Data: This tag contains all the level data.
  - [NBT Compound / JSON Object] Sections: Keys are stringified chunk section's Y coordinate (can be negative, a section at Y=2 starts at block Y=32).
    - [NBT Compound / JSON Object] <number>:
      - [Boolean] Valid: True (1) when created by the game, however, if the decoding of POI NBT (from the region file) data fails, and the game then save the region file again, it might save false (0). This key is internally set to true when the POI section is refreshed, and a refresh always happens when the chunk section (with terrain data) at the same coordinates is decoded. To sum up, it is very unlikely to get false.
      - [NBT List / JSON Array] Records: May be empty.
        [NBT Compound / JSON Object]: Single record.
        [Int Array] pos: 3-element array encoding X, Y and Z.
        
        [Int] free_tickets: Indicates how many "tickets" are available for villagers to claim. A value of zero indicates that this poi is not available for any villager to claim. Internally Minecraft specifies a max tickets for each poi type. This is the maximum number of villagers which can "take a ticket" (aka be using that poi type at the same time; aka max number of villagers which can claim that poi and store it in their "brain"). As of 1.17 all villager eligible poi type's have a ticket limit of one (1), with the single exception being minecraft:meeting, (block minecraft:bell) which has a limit of 32. Poi entries which are not for villager interaction such as beehives, nether portals, lighting rods, etc., have a max ticket count of zero (0) and therefore always have a free_tickets of zero as well.
        
        [String] type: Type of the point, for example: minecraft:home, minecraft:meeting, minecraft:butcher, minecraft:armorer, etc.
- [Int] DataVersion: An integer displaying the data version.

History

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level format History

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Java Edition
1.14	19w11a	The poi folder was added to world saves and village data is moved to it.
1.16	20w14a	Timestamps are no longer written to the session.lock file.
1.16	pre1	A single character ☃(E2 98 83) is now written to the session.lock file.
26.1	snap6	Restructured the entirety of the world save format :
		All default dimensions are now stored in the dimensions subfolder, removed the `DIM-1` and `DIM1` to `dimensions/minecraft/the_nether` and `dimensions/minecraft/the_end` respectively.
		The Overworld data has been moved to `dimensions/minecraft/overworld`, this includes the `region`, `entities`, and `poi` folders, as well as related files out of data.
		The top level `data` folder is now only for data shared across dimensions instead.
		Player storage has been moved to the `players` subdirectory : `advancements` `players/advancements`, `playerdata` -> `players/data`, `stats` -> `players/stats`.
		The world resource pack (`resources.zip`) has been moved to the `resourcepacks` subdirectory.
		Data saved in the data folder is now namespaced,All the data is stored in a namespace subfolder in the corresponding data folder, all existing vanilla data files have been moved accordingly.
		Command storage is now stored in namespace subfolders instead of having a namespace suffix.
		`chunks.dat` has been renamed to `chunk_tickets.dat`.
		Data for maps is now stored in the `data/minecraft/maps` subfolder, map index files have been renamed to only the number.
		`idcounts.dat` has been renamed to `last_id.dat`.
		There is no more `raids_end.dat` special case, the End now uses `raids.dat`.
		Structures saved by Structure Blocks have been moved from `generated/namespace/structures` to `generated/namespace/structure`.

level.dat History

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Java Edition
26.1	snap6	Restructured level.dat format :
		The [NBT Compound / JSON Object] Player tag in level.dat has been replaced with a [Int Array] singleplayer_uuid tag, referencing the player data file to use.
		Difficulty-related settings have been moved into a [NBT Compound / JSON Object] difficulty_settings tag.
		[Int] Difficulty is changed to [String] difficulty with theses allowed values : `peaceful`, `easy`, `normal` and `hard`, [Boolean] DifficultyLocked is renamed to [Boolean] locked.
		Data for the Ender Dragon fight has been moved out to the data folder to `dimensions/minecraft/the_end/data/minecraft/ender_dragon_fight.dat`
		Wandering Trader data has been moved out to the data folder to `data/minecraft/wandering_trader.dat`
		[NBT Compound / JSON Object] CustomBossEvents has been moved to the data folder to `data/minecraft/custom_boss_events.dat`
		Weather-related data has been moved to the data folder to `data/minecraft/weather.dat`
		[NBT Compound / JSON Object] ScheduledEvents has been moved out to the data folder to `data/minecraft/scheduled_events.dat`
		[NBT Compound / JSON Object] game_rules has been moved out to the data folder to `data/minecraft/game_rules.dat`
		[NBT Compound / JSON Object] WorldGenSettings has been moved out to the data folder to `data/minecraft/world_gen_settings.dat`
		[NBT Compound / JSON Object] world_clocks has been moved out to the data folder to `data/minecraft/world_clocks.dat`

weather.dat History

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Java Edition
26.1	snap6	Moved the weather data from `level.dat` to `data/minecraft/weather.dat`
		[Int] clearWeatherTime has been renamed to [Int] clear_weather_time
		[Int] rainTime has been renamed to [Int] rain_time
		[Int] thunderTime has been renamed to [Int] thunder_time

wandering_trader.dat History

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Java Edition
26.1	snap6	Moved the Wandering trader data from `level.dat` to `data/minecraft/wandering_trader.dat`
		[Int Array] WanderingTraderId has been removed.
		[Int] WanderingTraderSpawnChance has been renamed to [Int] spawn_chance
		[Int] WanderingTraderSpawnDelay has been renamed to [Int] spawn_delay

ender_dragon_fight.dat History

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Java Edition
26.1	snap6	Moved the Ender Dragon Fight data from `level.dat` to `data/minecraft/ender_dragon_fight.dat`
		[Undefined] NeedsStateScanning has been renamed to [Undefined] needs_state_scanning
		[Boolean] DragonKilled has been renamed to [Boolean] dragon_killed
		[Boolean] PreviouslyKilled has been renamed to [Boolean] previously_killed
		[Undefined] IsRespawning has been replaced by [Undefined] respawn_stage with theses allowed values : `start`, `preparing_to_summon_pillars`, `summoning_pillars`, `summoning_dragon`, `end`
		[Undefined] Dragon has been renamed to [Undefined] dragon_uuid
		[NBT Compound / JSON Object] ExitPortalLocation has been renamed to [NBT Compound / JSON Object] exit_portal_location
		[NBT List / JSON Array] Gateways has been renamed to [NBT List / JSON Array] gateways
		Added [Undefined] respawn_time, the time that has elapsed since the current stage of the respawn sequence started.
		Added [NBT List / JSON Array] respawn_crystals - a list of UUIDs for the end crystals used to trigger the respawn sequence.

scheduled_events.dat History

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Java Edition
26.1	snap6	Moved the Scheduled Events data from `level.dat` to `data/minecraft/scheduled_events.dat`
		[Undefined] Name has been renamed to [Undefined] id
		[Undefined] TriggerTime has been renamed to [Undefined] trigger_time
		[Undefined] Callback has been renamed to [Undefined] callback
		[Undefined] Type has been renamed to [Undefined] type

world_gen_settings.dat History

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Java Edition
26.1			snap6				Moved the World Generation Settings data from `level.dat` to `data/minecraft/world_gen_settings.dat`
26.1			snap6				[Boolean] generate_features has been renamed to [Boolean] generate_structures

References

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↑ http://www.reddit.com/r/Minecraft/comments/ywjbk/superflat_customization/c5zusxl

Navigation

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Java Edition technical

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URL: https://minecraft.wiki/w/Session.lock