Chunk format

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Chunks store the terrain and entities within a 16×256×16 area. They also store precomputed lighting, heightmap data for Minecraft's performance, and other meta information.

NBT structure[edit | edit source]

See also: Information from the Anvil format page

Chunks are stored in NBT format, with this structure (see Block Format below for the ordering of the blocks within each array):

  • The root tag.

    •  DataVersion: Version of the chunk NBT structure.

    •  Level: Chunk data.

      •  xPos: X position of the chunk.

      •  zPos: Z position of the chunk.

      •  LastUpdate: Tick when the chunk was last saved.

      •  LightPopulated: 1 or 0 (true/false) - If true, the server/client has already calculated lighting values for this chunk after generation.

      •  TerrainPopulated: 1 or not present (true/false) indicate whether the terrain in this chunk was populated with special things. (Ores, special blocks, trees, dungeons, flowers, waterfalls, etc.) If set to zero then Minecraft will regenerate these features in the blocks that already exist.

      •  V: Currently always saved as 1 and not actually loaded by the game. Likely a chunk version tag.

      •  InhabitedTime: The cumulative number of ticks players have been in this chunk. Note that this value increases faster when more players are in the chunk. Used for regional difficulty: increases the chances of mobs spawning with equipment, the chances of that equipment having enchantments, the chances of spiders having potion effects, the chances of mobs having the ability to pick up dropped items, and the chances of zombies having the ability to spawn other zombies when attacked. Note that at values 3600000 and above, regional difficulty is effectively maxed for this chunk. At values 0 and below, the difficulty is capped to a minimum (thus, if this is set to a negative number, it will behave identically to being set to 0, apart from taking time to build back up to the positives). See Regional Difficulty for more specifics.

      •  Biomes: May not exist. 256 bytes of biome data, one byte for each vertical column in the chunk. See Data Values for biome IDs. If this tag does not exist it will be created and filled by Minecraft when the chunk is loaded and saved. If any values in this array are -1, Minecraft will also set them to the correct biome.

      •  HeightMap: 1024 bytes(256 TAG_Int) of heightmap data. 16 × 16. Each byte records the lowest level in each column where the light from the sky is at full strength. Speeds computing of the SkyLight.

      •  Sections: List of Compound tags, each tag is a sub-chunk of sorts.

        • An individual Section.

          •  Y: The Y index (not coordinate) of this section. Range 0 to 15 (bottom to top), with no duplicates but some sections may be missing if empty.

          •  Blocks: 4096 bytes of block IDs defining the terrain. 8 bits per block, plus the bits from the below Add tag.

          •  Add: May not exist. 2048 bytes of additional block ID data. The value to add to (combine with) the above block ID to form the true block ID in the range 0 to 4095. 4 bits per block. Combining is done by shifting this value to the left 8 bits and then adding it to the block ID from above.

          •  Data: 2048 bytes of block data additionally defining parts of the terrain. 4 bits per block.

          •  BlockLight: 2048 bytes recording the amount of block-emitted light in each block. Makes load times faster compared to recomputing at load time. 4 bits per block.

          •  SkyLight: 2048 bytes recording the amount of sunlight or moonlight hitting each block. 4 bits per block.

      •  Entities: Each TAG_Compound in this list defines an entity in the chunk. See Entity Format below. If this list is empty it will be a list of End tags (before 1.10, list of Byte tags).

      •  TileEntities: Each TAG_Compound in this list defines a block entity in the chunk. See Block Entity Format below. If this list is empty it will be a list of End tags (before 1.10, list of Byte tags).

      •  TileTicks: May not exist. Each TAG_Compound in this list is an "active" block in this chunk waiting to be updated. These are used to save the state of redstone machines, falling sand or water, and other activity. See Tile Tick Format below. This tag may not exist.

Block format[edit | edit source]

In the Anvil format, block positions are ordered YZX for compression purposes.

The coordinate system is as follows:

  • X increases East, decreases West
  • Y increases upwards, decreases downwards
  • Z increases South, decreases North

This also happens to yield the most natural scan direction, because all indices in the least significant dimension (i.e. X in this case) appear for each index in the next most significant dimension; so one reads an array ordered YZX as one would a book lying with its top northward, all letters (or X-indices) on a single line (or Z-index) at a time, and all lines on a single page (or Y-index) at a time. For the 2D arrays (i.e. "Biomes" and "HeightMap") the inapplicable Y dimension is simply omitted, as though the book is only one page thick.

Each section in a chunk is a 16x16x16-block area, with up to 16 sections in a chunk. Section 0 is the bottom section of the chunk, and section 15 is the top section of the chunk. To save space, completely empty sections are not saved. Within each section is a byte tag "Y" for the Y index of the section, 0 to 15, and then byte arrays for the blocks. The "Block" byte array has 4096 partial block IDs at 8 bits per block. Another byte array "Add" is used for block with IDs over 255, and is 2048 bytes of the other part of the 4096 block IDs at 4 bits per block. When both the "Block" and "Add" byte arrays exist, the partial ID from the "Add" array is shifted left 8 bits and added to the partial ID from the "Blocks" array to form the true Block ID. The "Data" byte array is also 2048 bytes for 4096 block data values at 4 bits per block. The "BlockLight" and "SkyLight" byte arrays are the same as the "Data" byte array but they are used for block light levels and sky light levels respectively. The "SkyLight" values represent how much sunlight or moonlight can potentially reach the block, independent of the current light level of the sky.

The endianness of the 2048-byte arrays (i.e. "Add," "Data," "BlockLight," & "SkyLight"), which give only 4 bits per block, seems to stand as the one anomalous exception to the otherwise consistent, format-wide standard of big-endian data storage. It also runs counter to the presumably natural human-readable printing direction. If the blocks begin at 0, they are grouped with even numbers preceding odd numbers (i.e. 0 & 1 share a byte, 2 & 3 share the next, etc.); under these designations Minecraft stores even-numbered blocks in the least significant half-byte, and odd-numbered blocks in the most significant half-byte. Thus block[0] is byte[0] at 0x0F, block[1] is byte[0] at 0xF0, block[2] is byte[1] at 0x0F, block[3] is byte[1] at 0xF0, etc. ...

The pseudo-code below shows how to access individual block information from a single section. Hover over text to see additional information or comments.

byte Nibble4(byte[] arr, int index){ return index%2 == 0 ? arr[index/2]&0x0F : (arr[index/2]>>4)&0x0F; }
int BlockPos = y*16*16 + z*16 + x;
byte BlockID_a = Blocks[BlockPos];
byte BlockID_b = Nibble4(Add, BlockPos);
short BlockID = BlockID_a + (BlockID_b << 8);
byte BlockData = Nibble4(Data, BlockPos);
byte Blocklight = Nibble4(BlockLight, BlockPos);
byte Skylight = Nibble4(SkyLight, BlockPos);

Entity format[edit | edit source]

Every entity is an unnamed
 TAG_Compound contained in the Entities list of a chunk file. The sole exception is the Player entity, stored in level.dat, or in <player>.dat files on servers. All entities share this base:

id Pos Motion Rotation FallDistance Fire Air OnGround Dimension Invulnerable PortalCooldown UUIDMost UUIDLeast UUID CustomName CustomNameVisible Silent Riding CommandStats SuccessCountObjective SuccessCountName AffectedBlocksObjective AffectedBlocksName AffectedEntitiesObjective AffectedEntitiesName AffectedItemsObjective AffectedItemsName QueryResultObjective QueryResultName

  • Entity data

    •  id: Entity ID. This tag does not exist for the Player entity.

    •  Pos: 3 TAG_Doubles describing the current X,Y,Z position of the entity.

    •  Motion: 3 TAG_Doubles describing the current dX,dY,dZ velocity of the entity in meters per tick.

    •  Rotation: Two TAG_Floats representing rotation in degrees.

      • The entity's rotation clockwise around the Y axis (called yaw). Due west is 0. Does not exceed 360 degrees.

      • The entity's declination from the horizon (called pitch). Horizontal is 0. Positive values look downward. Does not exceed positive or negative 90 degrees.

    •  FallDistance: Distance the entity has fallen. Larger values cause more damage when the entity lands.

    •  Fire: Number of ticks until the fire is put out. Negative values reflect how long the entity can stand in fire before burning. Default -20 when not on fire.

    •  Air: How much air the entity has, in ticks. Fills to a maximum of 300 in air, giving 15 seconds submerged before the entity starts to drown, and a total of up to 35 seconds before the entity dies (if it has 20 health). Decreases while underwater. If 0 while underwater, the entity loses 1 health per second.

    •  OnGround: 1 or 0 (true/false) - true if the entity is touching the ground.

    •  NoGravity: 1 or 0 (true/false) - if true, the entity will not fall if in the air.

    •  Dimension: Only known to be used in <player>.dat to store the players last known location along with Pos. All other entities are only saved in the region files for the dimension they are in. -1 for The Nether, 0 for The Overworld, and 1 for The End.

    •  Invulnerable: 1 or 0 (true/false) - true if the entity should not take damage. This applies to living and nonliving entities alike: mobs will not take damage from any source (including potion effects), and cannot be moved by fishing rods, attacks, explosions, or projectiles, and objects such as vehicles and item frames cannot be destroyed unless their supports are removed. Note that these entities can be damaged by players in Creative mode.

    •  PortalCooldown: The number of ticks before which the entity may be teleported back through a nether portal. Initially starts at 300 ticks (15 seconds) after teleportation and counts down to 0.

    •  UUIDMost: The most significant bits of this entity's Universally Unique IDentifier. This is joined with UUIDLeast to form this entity's unique ID.

    •  UUIDLeast: The least significant bits of this entity's Universally Unique IDentifier.

    •  UUID (removed in 1.9): The Universally Unique IDentifier of this entity. Converts a hexadecimal UUID (for example: 069a79f4-44e9-4726-a5be-fca90e38aaf5) into the UUIDLeast and UUIDMost tags. Will not apply new UUIDLeast and UUIDMost tags if both of these tags are already present. The "UUID" tag is removed once the entity is loaded.

    •  CustomName: The custom name of this entity. Appears in player death messages and villager trading interfaces, as well as above the entity when your cursor is over it. May not exist, or may exist and be empty.

    •  CustomNameVisible: 1 or 0 (true/false) - if true, and this entity has a custom name, it will always appear above them, whether or not the cursor is pointing at it. If the entity hasn't a custom name, a default name will be shown. May not exist.

    •  Silent: 1 or 0 (true/false) - if true, this entity will not make sound. May not exist.

    •  Riding: (deprecated in 1.9) The data of the entity being ridden. Note that if an entity is being ridden, the topmost entity in the stack has the Pos tag, and the coordinates specify the location of the bottommost entity. Also note that the bottommost entity controls movement, while the topmost entity determines spawning conditions when created by a mob spawner.
      • See this format (recursive).

    •  Passengers: The data of the entity riding. Note that both entities control movement and the topmost entity controls spawning conditions when created by a mob spawner.
      • See this format (recursive).

    •  Glowing: 1 or 0 (true/false) - true if the entity has a glowing outline.

    •  Tags: List of custom string data.

    •  CommandStats: Information identifying scoreboard parameters to modify relative to the last command run

      •  SuccessCountObjective: Objective's name about the number of successes of the last command (will be an int)

      •  SuccessCountName: Fake player name about the number of successes of the last command

      •  AffectedBlocksObjective: Objective's name about how many blocks were modified in the last command (will be an int)

      •  AffectedBlocksName: Fake player name about how many blocks were modified in the last command

      •  AffectedEntitiesObjective: Objective's name about how many entities were altered in the last command (will be an int)

      •  AffectedEntitiesName: Fake player name about how many entities were altered in the last command

      •  AffectedItemsObjective: Objective's name about how many items were altered in the last command (will be an int)

      •  AffectedItemsName: Fake player name about how many items were altered in the last command

      •  QueryResultObjective: Objective's name about the query result of the last command

      •  QueryResultName: Fake player name about the query result of the last command

Mobs[edit | edit source]

Mob Entities
Entity ID Name
Bat Bat
Blaze Blaze
CaveSpider Cave Spider
Chicken[note 1] Chicken
Cow[note 1] Cow
Creeper Creeper
EnderDragon Ender Dragon
Enderman Enderman
Endermite Endermite
Ghast Ghast
Giant Giant
Guardian Guardian
Elder Guardian
EntityHorse[note 1] Horse
LavaSlime Magma Cube
MushroomCow[note 1] Mooshroom
Ozelot[note 1][note 2] Ocelot
Pig[note 1] Pig
PigZombie Zombie Pigman
PolarBear Polar Bear
Rabbit[note 1] Rabbit
Sheep[note 1] Sheep
Shulker Shulker
Silverfish Silverfish
Skeleton Skeleton
Wither Skeleton
Slime Slime
SnowMan Snow Golem
Spider Spider
Squid Squid
Villager[note 1] Villager
VillagerGolem Iron Golem
Witch Witch
WitherBoss Wither
Wolf[note 1][note 2] Wolf
Zombie Zombie
Zombie Villager
  1. a b c d e f g h i j Can breed
  2. a b Can be tamed

Mobs are a subclass of Entity with additional tags to store their health, attacking/damaged state, potion effects, and more depending on the mob. Players are a subclass of Mob.

Projectiles[edit | edit source]

Projectile Entities
Entity ID Name
Arrow Arrow
DragonFireball Ender Dragon Fireball
Fireball Ghast Fireball
SmallFireball Blaze Fireball/Fire Charge
Snowball Snowball
SpectralArrow Spectral Arrow
ThrownEgg Egg
ThrownEnderpearl Ender Pearl
ThrownExpBottle Bottle o' Enchanting
ThrownPotion Splash Potion
WitherSkull Wither Skull

Projectiles are a subclass of Entity and have very obscure tags such as X,Y,Z coordinate tags despite Entity Pos tag, inTile despite inGround, and shake despite most projectiles not being arrows. While all projectiles share tags, they are all independently implemented through Throwable, ArrowBase, and FireballBase.

Items and XPOrbs[edit | edit source]

Item Entities
Entity ID Name
Item Dropped Item
XPOrb Experience Orb

Items and XPOrbs are a subclass of Entity.

Vehicles[edit | edit source]

Vehicle Entities
Entity ID Name
Boat Boat
Minecart (deprecated) Minecart
Minecart with Chest
Minecart with Furnace
MinecartRideable Minecart
MinecartChest Minecart with Chest
MinecartFurnace Minecart with Furnace
MinecartSpawner Minecart with Spawner
MinecartTNT Minecart with TNT
MinecartHopper Minecart with Hopper
MinecartCommandBlock Minecart with Command Block

Vehicles are subclasses of Entity.

Dynamic tiles[edit | edit source]

Dynamic Block Entities
Entity ID Name
PrimedTnt TNT
FallingSand Dynamic Tile

Dynamic tiles are a subclass of Entity and are used to simulate realistically moving blocks.

Other[edit | edit source]

Other Entities
Entity ID Name
AreaEffectCloud Area Effect Cloud
ArmorStand Armor Stand
EnderCrystal Ender Crystal
evocation_fangs Evocation Fangs
EyeOfEnderSignal Eye of Ender
FireworksRocketEntity Firework Rocket
ItemFrame Item Frame
LeashKnot Lead Knot
Painting Painting
ShulkerBullet Shulker Bullet
Fishing Rod Bobber
Llama spit

Other entity types that are a subclass of Entity but do not fit into any of the above categories.

Block entity format[edit | edit source]

Block Entities
Block Entity ID Associated Block
Airportal End Portal (block)
Banner Banner
Beacon Beacon
Cauldron (Computer Edition) Brewing Stand
Cauldron (PE) Cauldron
Chest Chest
Trapped Chest
Comparator Redstone Comparator
Control Command Block
DLDetector Daylight Sensor
Dropper Dropper
EnchantTable Enchantment Table
EnderChest Ender Chest
EndGateway End Gateway (block)
FlowerPot Flower Pot
Furnace Furnace
Hopper Hopper
MobSpawner Monster Spawner
Music Note Block
Piston Piston Moving
RecordPlayer Jukebox
Sign Sign
Skull Mob head
Structure Structure Block
Trap Dispenser

A block entity (not related to entity) is used by Minecraft to store information about a block that can't be stored in the four bits of block data the block has. Block entities were called "tile entities" until the 1.8 snapshots and that term is still used in some command usage.