Chunk Format
Byte Order
Chunk data is stored in Big Endian byte order unless mentioned otherwise.
Chunk NBT Data
| Tag Name | Tag Type | Description |
|---|---|---|
| DataVersion | IntTag | Version of the chunk NBT structure. |
| Level | CompoundTag | Chunk Data |
Level Data
| Tag Name | Tag Type | Description |
|---|---|---|
| xPos | IntTag | X position of the chunk (in absolute chunks from x, z origin, not relative to the region). |
| zPos | IntTag | Z position of the chunk (in absolute chunks from x, z origin, not relative to the region). |
| Status | StringTag | Defines the world generation status of this chunk. It is always one of the following: empty, structure_starts, structure_references, biomes, noise, surface, carvers, liquid_carvers, features, light, spawn, heightmaps, or full. All status except full are used for chunks called proto-chunks, in other words, for chunks with incomplete generation. |
| LastUpdate | LongTag | Tick when the chunk was last saved. |
| InhabitedTime | LongTag | 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. |
| Biomes | IntArrayTag | 1024 entries of biome data. Each number in the array is the biome id for a 4×4×4 volume in the chunk. These 4×4×4 volumes are arranged by Z, then X, then Y. That is, the first 4×4 values in the array are for the 16×16 chunk, at Y levels 0-3, the next 4×4 is for Y levels 4-7, etc. If this tag does not exist, it gets created and filled by Minecraft. |
| Heightmaps | CompoundTag | Several different heightmaps corresponding to 256 values compacted at 9 bits per word (lowest being 0, highest being 256, both inclusive). |
| Sections | ListTag of CompoundTags | Each CompoundTag is a section (also known as subchunk). All sections in the world’s height are present in this list. Empty sections are not stored. |
| Entities | ListTag of CompoundTags | Each CompoundTag in this list defines a entity in this chunk. (Removed in 1.17) |
| TileEntities | ListTag of CompoundTags | Each CompoundTag in this list defines a block entity in this chunk. |
| TileTicks | ListTag of CompoundTags | Each CompoundTag in this list is an “active” block in this chunk waiting to be updated. |
| LiquidTicks | ListTag of CompoundTags | Each CompoundTag in this list is an “active” liquid in this chunk waiting to be updated. |
| Lights | ListTag of 16 ListTags of ShortTags | |
| LiquidsToBeTicked | ListTag of 16 ListTags of ShortTags | |
| ToBeTicked | ListTag of 16 ListTags of ShortTags | |
| PostProcessing | ListTag of 16 ListTags of ShortTags | |
| Structures | CompoundTag | Structure data in this chunk. |
Heightmaps Data
| Tag Name | Tag Type | Description |
|---|---|---|
| MOTION_BLOCKING | LongArrayTag | The highest block that blocks motion or contains a fluid. Longs are stored in Little Endian |
| MOTION_BLOCKING_NO_LEAVES | LongArrayTag | The highest block that blocks motion, contains a fluid, or is in the minecraft:leaves tag. Longs are stored in Little Endian |
| OCEAN_FLOOR | LongArrayTag | The highest block that is neither air or a fluid. Longs are stored in Little Endian |
| OCEAN_FLOOR_WG | LongArrayTag | The highest block that is neither air or a fluid, for worldgen. Longs are stored in Little Endian |
| WORLD_SURFACE | LongArrayTag | The highest non-air block. Longs are stored in Little Endian |
| WORLD_SURFACE_WG | LongArrayTag | The highest non-air block, for worldgen. Longs are stored in Little Endian |
Section Data
Palette Data
| Tag Name | Tag Type | Description |
|---|---|---|
| Name | StringTag | Block resource location. |
| Properties | CompoundTag | List of block state properties. Omitted if block has no properties. |
Entities Data
An entities data. See the Minecraft Wiki page for details.
Tile Entities Data
A tile entities data. See the Minecraft Wiki page for details.
Tile Ticks Data
| Tag Name | Tag Type | Description |
|---|---|---|
| i | StringTag | The ID of the block; used to activate the correct block update procedure. |
| p | IntTag | If multiple tile ticks are scheduled for the same tick, tile ticks with lower p are processed first. If they also have the same p, order is unknown. |
| t | IntTag | The number of ticks until processing should occur. May be negative when processing is overdue. |
| x | IntTag | X position. |
| y | IntTag | Y position. |
| z | IntTag | Z position. |
Structures Data
Structure data in this chunk. See NBT structure for structures on the Minecraft Wiki page for more details.
Parsing the Chunk
Parsing the Blocks
Variables you’ll need to calculate first
| Name | Type | Formula |
|---|---|---|
| Bits Per Word | 32-bit integer | 64 - leadingZeros(palette.len()) |
| Blocks Per Word | 32-bit integer | floor(64 ÷ Bits Per Word) |
| Block Indices | 32-bit integer array. Size = ceil(4096 ÷ Blocks Per Word) × Blocks Per Word | Extract Blocks Per Word indices of Bits Per Word bits from each 64-bit integer and store them as their own index in the new 32-bit integer array |
Now that you have all the needed variables you can now loop the palette in XZY order (X increments first).
The index can be calculated with Y × 16 × 16 + Z × 16 + X.
Indexing the block palette should look something like this: palette.get(block_indices[xzy_index])
Parsing the Biomes
Loop the biome id array in XZY order (X increments first).
The index can be calculated with (Y >> 2 & 0x3) × 16 + (Z >> 2 & 0x3) × 4 + (X >> 2 & 0x3).
Indexing the biomes is like a normal array: biomes[xzy_index].
Parsing the Heightmaps
Variables you’ll need to calculate first
| Name | Type | Formula |
|---|---|---|
| Block Indices | 32-bit integer array. Size = 259 (Only 256 indices used) | Extract 7 indices of 9 bits from each 64-bit integer and store them as their own index in the new 32-bit integer array |
Now that you have all the needed variables you can now loop the palette in XZ order (X increments first).
The index can be calculated with Z × 16 + X.
Indexing the heightmap arrays is like a normal array: heightmap[xz_index].