Chunk Format

Revision as of 20:12, 9 April 2016 by Pokechu22 (talk | contribs) (→‎Format: Note about damage values)
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Warning.png This information, particularly about the palette and when it can be omitted, is incorrect. The article will be corrected as this format is researched and reverse-engineered. Sorry for any inconvenience. --Pokechu22 (talk) 01:46, 5 April 2016 (UTC)

This article describes the Chunk Section format used in the Chunk Data packet (Play, 0x20, clientbound).


  • Chunk Section: a 16×16×16 area, sometimes also called chunk.
  • Chunk Column: 16 chunks aligned vertically (totalling 16×256×16).


A Chunk Section is defined in terms of other data types. A Chunk Section consists of the following fields:

Field Name Field Type Notes
Bits Per Block Unsigned Byte Determines how many bits are used to encode a block. Note that the actual value does not always match this value.
Palette Length VarInt Length of the following array. May be 0.
Palette Array of VarInt Mapping of block state IDs in the global palette to indices of this array
Data Array Length VarInt Number of bytes in the following array
Data Array Long Array List of 4096 indices pointing to state IDs in the Palette
Block Light Byte Array Half byte per block
Sky Light Optional Byte Array Only if in the Overworld; half byte per block

Data Array, Block Light, and Sky Light are given for each block with increasing x coordinates, within rows of increasing z coordinates, within layers of increasing y coordinates.

The format of the palette changes based off of the value of bits per block.

  • 0: The palette array has a length of 0, but no actual blocks can be sent since each block is represented by 0 bits. This generally shouldn't be done as instead the primary bit mask should be used to mark this chunk section as empty.
  • 1 to 4: Blocks are encoded as 4 bits. The palette array is at max 16 entries long and is used.
  • 5 to 8: Blocks are encoded with the given number of bits.
  • 9 and above: The palette array has a length of 0, and blocks are always represented as 13 bits per block in reference to the global palette.

The global palette encodes a block as 13 bits. It uses the block ID for the first 9 bits, and the block damage value for the last 4 bits. For example, diorite (block ID 1 for minecraft:stone with damage 3) would be encoded as 000000001 0011. If the damage value is not valid for a block, then the block will be treated as air.

In half-byte arrays, two values are packed into each byte. Even-indexed items are packed into the low bits, odd-indexed into the high bits.


The following implement the previous (before 1.9) format: