Pre-release protocol

This page documents the changes from the last stable Minecraft release (currently 1.17.1, protocol 756) to the current pre-release (currently 1.18-rc1, protocol Snapshot 57). Note that this page contains bleeding-edge information that may not be completely or correctly documented.

One who wishes to commandeer the merging of this into Protocol when an update is made must be sure to respect any changes that may have occurred to the respective packets there.

Contents

Data types

• Chunk Section

Packets

ID	Packet name	Documentation
Play clientbound
0x0A	Block Entity Data	Current	Pre
0x22	Chunk Data and Update Light	Current	Pre
0x26	Join Game	Current	Pre
0x57	Update Simulation Distance		Pre
0x57 0x58	Set Title SubTitle	Current	(unchanged)
0x58 0x59	Time Update	Current	(unchanged)
0x59 0x5A	Set Title Text	Current	(unchanged)
0x5A 0x5B	Set Title Times	Current	(unchanged)
0x5B 0x5C	Entity Sound Effect	Current	(unchanged)
0x5C 0x5D	Sound Effect	Current	(unchanged)
0x5D 0x5E	Stop Sound	Current	(unchanged)
0x5E 0x5F	Player List Header And Footer	Current	(unchanged)
0x5F 0x60	NBT Query Response	Current	(unchanged)
0x60 0x61	Collect Item	Current	(unchanged)
0x61 0x62	Entity Teleport	Current	(unchanged)
0x62 0x63	Advancements	Current	(unchanged)
0x63 0x64	Entity Properties	Current	(unchanged)
0x64 0x65	Entity Effect	Current	(unchanged)
0x65 0x66	Declare Recipes	Current	(unchanged)
0x66 0x67	Tags	Current	(unchanged)
Play serverbound
0x05	Client Settings	Current	Pre

New/modified data types

Chunk Section

The data section of the packet contains most of the useful data for the chunk.

Field Name	Field Type	Notes
Data	Array of Chunk Section	The number of elements in the array is equal to the number of bits set in Primary Bit Mask calculated based on the world's height. Sections are sent bottom-to-top, i.e. the first section, if sent, extends from Y=0 to Y=15.

Chunk Section structure

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

Field Name	Field Type	Notes
Block count	Short	Number of non-air blocks present in the chunk section. "Non-air" is defined as any block other than air, cave air, and void air (in particular, note that fluids such as water are still counted). The client uses this to unload chunks empty chunks. It will keep count of the blocks as they are broken/placed and if this integer reaches 0 the whole chunk section is not rendered, even though there may still be blocks left, if the server sends an incorrect block count.
Bits Per Block	Unsigned Byte	Determines how many bits are used to encode a block. Note that not all numbers are valid here.
Palette	Varies	See below for the format.
Data Array Length	VarInt	Number of longs in the following array
Data Array	Array of Long	Compacted list of 4096 (16x16x16) indices pointing to state IDs in the Palette (see Compacted data array)
Block states	Paletted Container	Consists of 4096 entries, representing all the blocks in the chunk section
Biomes	Paletted Container	Consists of 64 entries, representing 4x4x4 biome regions in the chunk section

Paletted Container structure

A Paletted Container is a palette-based storage of entries. Paletted Containers have an associated global palette (either block states or biomes as of now), where values are mapped from. A Paletted Container consists of the following fields:

Field Name	Field Type	Notes
Bits Per Entry	Unsigned Byte	Determines how many bits are used to encode entries. Note that not all numbers are valid here.
Palette	Varies	See below for the format.
Data Array Length	VarInt	Number of longs in the following array
Data Array	Array of Long	Compacted list of indices pointing to entry IDs in the Palette. When Bits Per Entry is 0, this array is empty (see Single valued palette)

Data Array is given for each entry with increasing x coordinates, within rows of increasing z coordinates, within layers of increasing y coordinates.

Palettes

The bits per block entry value determines what format is used for the palette. In most cases, invalid values will be interpreted as a different value when parsed by the notchian client, meaning that chunk data will be parsed incorrectly if you use an invalid bits per block entry. Servers must make sure that the bits per block entry value is correct. There are currently three types of palettes:

Single valued

This format is used when bits per entry is equal to 0, and signifies that the palette contains a single value. When this palette is used, the Data Array sent/received is empty, since entries can be inferred from the palette's single value.

The format is as follows:

Field Name	Field Type	Notes
Value	VarInt	ID of the corresponding entry in its global palette

Indirect

There are two three variants of this:

• For block states and bits per block entry <= 4, 4 bits are used to represent a block.
• For block states and bits per block entry between 5 and 8, the given value is used.
• For biomes and bits per entry <= 3, the given value is used.

This is an actual palette which lists the block states entries used. Values in the chunk section's data array are indices into the palette, which in turn gives a proper block state entry.

The format is as follows:

Field Name	Field Type	Notes
Palette Length	VarInt	Number of elements in the following array.
Palette	Array of VarInt	Mapping of block state entry IDs in the global palette to indices of this array

Direct

This format is used for bits per block entry values greater than or equal to 9 a threshold (9 for block states, 4 for biomes). The number of bits used to represent a block an entry is the base 2 logarithm of the number of block states entries in the global palette, rounded up. For the current vanilla release, this is 15 bits per block per entry for block states, and 6 bits per entry for biomes.

The "palette" uses the following format:

Field Name	Field Type	Notes
no fields

Entity Metadata

No changes so far.

Entity

No changes so far.

Block Actions

No changes so far.

Inventories

No changes so far.

Plugin Channels

No changes so far.

Play

Clientbound

Block Entity Data

Sets the block entity associated with the block at the given location.

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x0A	Play	Client	Location	Position
			Action	Unsigned Byte	The type of update to perform, see below.
			Type	VarInt	The type of block entity
			NBT Data	NBT Tag	Data to set. May be a TAG_END (0), in which case the block entity at the given location is removed (though this is not required since the client will remove the block entity automatically on chunk unload or block removal).

Chunk Data and Update Light

Main article: Chunk Format

See also: #Unload Chunk

	The following information needs to be added to this page:
	How do biomes work now? The biome change happened at the same time as the seed change, but it's not clear how/if biomes could be computed given that it's not the actual seed... (/r/mojira discussion which notes that it seems to be some kind of interpolation, and 3D biomes are only used in the nether)

The server only sends skylight information for chunk pillars in the Overworld, it's up to the client to know in which dimension the player is currently located. You can also infer this information from the primary bitmask and the amount of uncompressed bytes sent. This packet also sends all block entities in the chunk (though sending them is not required; it is still legal to send them with Update Block Entity later). See Light for information on how lighting works in Minecraft.

Packet ID	State	Bound To	Field Name		Field Type		Notes
0x22	Play	Client	Chunk X		Int		Chunk coordinate (block coordinate divided by 16, rounded down)
			Chunk Z		Int		Chunk coordinate (block coordinate divided by 16, rounded down)
			Primary Bit Mask		BitSet		BitSet of length world height in chunk sections, i.e. height / 16. Bits are set to 1 for every 16×16×16 chunk section whose data is included in Data. The least significant bit represents the chunk section at the bottom of the chunk column (from the lowest y to 15 blocks above).
			Heightmaps		NBT		Compound containing one long array named MOTION_BLOCKING, which is a heightmap for the highest solid block at each position in the chunk (as a compacted long array with 256 entries at 9 bits per entry totaling 36 longs , with the number of bits per entry varying depending on the world's height, defined by the formula ceil(log2(height + 1))). The Notchian server also adds a WORLD_SURFACE long array, the purpose of which is unknown, but it's not required for the chunk to be accepted.
			Biomes length		VarInt		Size of the following array; should always be 1024. Not present if full chunk is false.
			Biomes		Array of VarInt		1024 biome IDs, ordered by x then z then y, in 4×4×4 blocks. Not present if full chunk is false. See Chunk Format § Biomes.
			Size		VarInt		Size of Data in bytes
			Data		Byte array		See data structure in Chunk Format
			Number of block entities		VarInt		Number of elements in the following array
			Block entities		Array of NBT Tag		All block entities in the chunk. Use the x, y, and z tags in the NBT to determine their positions.
			Block Entity	Packed XZ	Array	Byte	The packed section coordinates, calculated from ((blockX & 15) << 4) | (blockZ & 15)
				Y		Short	The height relative to the world
				Type		VarInt	The type of block entity
				Data		NBT	The block entity's data, without the X, Y, and Z values
			Trust Edges		Boolean		If edges should be trusted for light updates.
			Sky Light Mask		BitSet		BitSet containing bits for each section in the world + 2. Each set bit indicates that the corresponding 16×16×16 chunk section has data in the Sky Light array below. The least significant bit is for blocks 16 blocks to 1 block below the min world height (one section below the world), while the most significant bit covers blocks 1 to 16 blocks above the max world height (one section above the world).
			Block Light Mask		BitSet		BitSet containing bits for each section in the world + 2. Each set bit indicates that the corresponding 16×16×16 chunk section has data in the Block Light array below. The order of bits is the same as in Sky Light Mask.
			Empty Sky Light Mask		BitSet		BitSet containing bits for each section in the world + 2. Each set bit indicates that the corresponding 16×16×16 chunk section has all zeros for its Sky Light data. The order of bits is the same as in Sky Light Mask.
			Empty Block Light Mask		BitSet		BitSet containing bits for each section in the world + 2. Each set bit indicates that the corresponding 16×16×16 chunk section has all zeros for its Block Light data. The order of bits is the same as in Sky Light Mask.
			Sky Light array count		VarInt		Number of entries in the following array; should match the number of bits set in Sky Light Mask
			Sky Light arrays	Length	Array	VarInt	Length of the following array in bytes (always 2048)
				Sky Light array		Array of 2048 bytes	There is 1 array for each bit set to true in the sky light mask, starting with the lowest value. Half a byte per light value.
			Block Light array count		VarInt		Number of entries in the following array; should match the number of bits set in Block Light Mask
			Block Light arrays	Length	Array	VarInt	Length of the following array in bytes (always 2048)
				Block Light array		Array of 2048 bytes	There is 1 array for each bit set to true in the block light mask, starting with the lowest value. Half a byte per light value.

Note that the Notchian client requires an Update View Position packet when it crosses a chunk border, otherwise it'll only display render distance + 2 chunks around the chunk it spawned in.

The compacted array format has been adjusted so that individual entries no longer span across multiple longs, affecting the main data array and heightmaps.

New format, 5 bits per block, containing the following references to blocks in a palette (not shown): 122344566480743131516914101202

0020863148418841 0000000000100000100001100011000101001000010000011000100001000001
01018A7260F68C87 0000000100000001100010100111001001100000111101101000110010000111

A bit will never be set in both the block light mask and the empty block light mask, though it may be present in neither of them (if the block light does not need to be updated for the corresponding chunk section). The same applies to the sky light mask and the empty sky light mask.

Join Game

See Protocol Encryption for information on logging in.

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x26	Play	Client	Entity ID	Int	The player's Entity ID (EID).
			Is hardcore	Boolean
			Gamemode	Unsigned Byte	0: Survival, 1: Creative, 2: Adventure, 3: Spectator.
			Previous Gamemode	Byte	0: survival, 1: creative, 2: adventure, 3: spectator. The hardcore flag is not included. The previous gamemode. Defaults to -1 if there is no previous gamemode. (More information needed)
			World Count	VarInt	Size of the following array.
			World Names	Array of Identifier	Identifiers for all worlds on the server.
			Dimension Codec	NBT Tag Compound	The full extent of these is still unknown, but the tag represents a dimension and biome registry. See below for the vanilla default.
			Dimension	NBT Tag Compound	Valid dimensions are defined per dimension registry sent before this. The structure of this tag is a dimension type (see below).
			World Name	Identifier	Name of the world being spawned into.
			Hashed seed	Long	First 8 bytes of the SHA-256 hash of the world's seed. Used client side for biome noise
			Max Players	VarInt	Was once used by the client to draw the player list, but now is ignored.
			View Distance	VarInt	Render distance (2-32).
			Simulation Distance	VarInt	The distance that the client will process specific things, such as entities.
			Reduced Debug Info	Boolean	If true, a Notchian client shows reduced information on the debug screen. For servers in development, this should almost always be false.
			Enable respawn screen	Boolean	Set to false when the doImmediateRespawn gamerule is true.
			Is Debug	Boolean	True if the world is a debug mode world; debug mode worlds cannot be modified and have predefined blocks.
			Is Flat	Boolean	True if the world is a superflat world; flat worlds have different void fog and a horizon at y=0 instead of y=63.

The Dimension Codec NBT Tag Compound (Default value in SNBT) includes two registries: "minecraft:dimension_type" and "minecraft:worldgen/biome".

Name	Type	Notes
minecraft:dimension_type	TAG_Compound	The dimension type registry (see below).
minecraft:worldgen/biome	TAG_Compound	The biome registry (see below).

Dimension type registry:

Name	Type	Notes
type	TAG_String	The name of the registry. Always "minecraft:dimension_type".
value	TAG_List	List of dimension types registry entries (see below).

Dimension type registry entry:

Name	Type	Notes
name	TAG_String	The name of the dimension type (for example, "minecraft:overworld").
id	TAG_Int	The protocol ID of the dimension (matches the index of the element in the registry list).
element	TAG_Compound	The dimension type (see below).

Dimension type:

Name	Type	Meaning		Values
piglin_safe	TAG_Byte	Whether piglins shake and transform to zombified piglins.		1: true, 0: false.
natural	TAG_Byte	When false, compasses spin randomly. When true, nether portals can spawn zombified piglins.		1: true, 0: false.
ambient_light	TAG_Float	How much light the dimension has.		0.0 to 1.0.
fixed_time	Optional TAG_Long	If set, the time of the day is the specified value.		If set, 0 to 24000.
infiniburn	TAG_String	A resource location defining what block tag to use for infiniburn.		"" or minecraft resource "minecraft:...".
respawn_anchor_works	TAG_Byte	Whether players can charge and use respawn anchors.		1: true, 0: false.
has_skylight	TAG_Byte	Whether the dimension has skylight access or not.		1: true, 0: false.
bed_works	TAG_Byte	Whether players can use a bed to sleep.		1: true, 0: false.
effects	TAG_String	?		"minecraft:overworld", "minecraft:the_nether", "minecraft:the_end" or something else.
has_raids	TAG_Byte	Whether players with the Bad Omen effect can cause a raid.		1: true, 0: false.
min_y	TAG_Int	The minimum Y level.
height	TAG_Int	The maximum height.
logical_height	TAG_Int	The maximum height to which chorus fruits and nether portals can bring players within this dimension.		0-256.
coordinate_scale	TAG_Float	The multiplier applied to coordinates when traveling to the dimension.		0.00001 - 30000000.0
ultrawarm	TAG_Byte	Whether the dimensions behaves like the nether (water evaporates and sponges dry) or not. Also causes lava to spread thinner.		1: true, 0: false.
has_ceiling	TAG_Byte	Whether the dimension has a bedrock ceiling or not. When true, causes lava to spread faster.		1: true, 0: false.

Biome registry:

Name	Type	Notes
type	TAG_String	The name of the registry. Always "minecraft:worldgen/biome".
value	TAG_List	List of biome registry entries (see below).

Biome registry entry:

Name	Type	Notes
name	TAG_String	The name of the biome (for example, "minecraft:ocean").
id	TAG_Int	The protocol ID of the biome (matches the index of the element in the registry list).
element	TAG_Compound	The biome properties (see below).

Biome properties:

Name		Type		Meaning		Values
precipitation		TAG_String		The type of precipitation in the biome.		"rain", "snow", or "none".
depth		TAG_Float		The depth factor of the biome.		The default values vary between 1.5 and -1.8.
temperature		TAG_Float		The temperature factor of the biome.		The default values vary between 2.0 and -0.5.
scale		TAG_Float		?		The default values vary between 1.225 and 0.0.
downfall		TAG_Float		?		The default values vary between 1.0 and 0.0.
category		TAG_String		The category of the biome.		Known values are "ocean", "plains", "desert", "forest", "extreme_hills", "taiga", "swamp", "river", "nether", "the_end", "icy", "mushroom", "beach", "jungle", "mesa", "savanna", and "none".
temperature_modifier		Optional TAG_String		?		The only known value is "frozen".
effects	sky_color	TAG_Compound	TAG_Int	The color of the sky.		Example: 8364543, which is #7FA1FF in RGB.
	water_fog_color		TAG_Int	Possibly the tint color when swimming.		Example: 8364543, which is #7FA1FF in RGB.
	fog_color		TAG_Int	Possibly the color of the fog effect when looking past the view distance.		Example: 8364543, which is #7FA1FF in RGB.
	water_color		TAG_Int	The tint color of the water blocks.		Example: 8364543, which is #7FA1FF in RGB.
	foliage_color		Optional TAG_Int	The tint color of the grass.		Example: 8364543, which is #7FA1FF in RGB.
	grass_color		Optional TAG_Int	?		Example: 8364543, which is #7FA1FF in RGB.
	grass_color_modifier		Optional TAG_String	Unknown, likely affects foliage color.		If set, known values are "swamp" and "dark_forest".
	music		Optional TAG_Compound	Music properties for the biome.		If present, contains the fields: replace_current_music (TAG_Byte), sound (TAG_String), max_delay (TAG_Int), min_delay (TAG_Int).
	ambient_sound		Optional TAG_String	Ambient soundtrack.		If present, the ID of a soundtrack. Example: "minecraft:ambient.basalt_deltas.loop".
	additions_sound		Optional TAG_Compound	Additional ambient sound that plays randomly.		If present, contains the fields: sound (TAG_String), tick_chance (TAG_Double).
	mood_sound		Optional TAG_Compound	Additional ambient sound that plays at an interval.		If present, contains the fields: sound (TAG_String), tick_delay (TAG_Int), offset (TAG_Double), block_search_extent (TAG_Int).
particle	probability	Optional TAG_Compound	TAG_FLOAT	Particles that appear randomly in the biome.	Possibly the probability of spawning the particle.	?
	options		TAG_COMPOUND		The properties of the particle to spawn.	Contains the field "type" (TAG_String), which identifies the particle type.

Update Simulation Distance

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x26	Play	Client	Simulation Distance	VarInt	The distance that the client will process specific things, such as entities.

Serverbound

Client Settings

Sent when the player connects, or when settings are changed.

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x05	Play	Server	Locale	String (16)	e.g. en_GB.
			View Distance	Byte	Client-side render distance, in chunks.
			Chat Mode	VarInt Enum	0: enabled, 1: commands only, 2: hidden. See processing chat for more information.
			Chat Colors	Boolean	“Colors” multiplayer setting.
			Displayed Skin Parts	Unsigned Byte	Bit mask, see below.
			Main Hand	VarInt Enum	0: Left, 1: Right.
			Disable text filtering	Boolean	Disables filtering of text on signs and written book titles. Currently always true (i.e. the filtering is disabled)
			Allow server listings	Boolean	Servers usually list online players, this option should let you not show up in that list.

Displayed Skin Parts flags:

• Bit 0 (0x01): Cape enabled
• Bit 1 (0x02): Jacket enabled
• Bit 2 (0x04): Left Sleeve enabled
• Bit 3 (0x08): Right Sleeve enabled
• Bit 4 (0x10): Left Pants Leg enabled
• Bit 5 (0x20): Right Pants Leg enabled
• Bit 6 (0x40): Hat enabled

The most significant bit (bit 7, 0x80) appears to be unused.

Status

Clientbound

No changes so far.

Serverbound

No changes so far.

Login

Clientbound

No changes so far.

Serverbound

No changes so far.