Pre-release protocol

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This page documents the changes from the last stable Minecraft release (currently 1.13.2, protocol 404) to the current pre-release (currently 18w43b, protocol 441). 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

No changes so far.

Packets

ID Packet name Documentation
Handshaking serverbound
0x00 Handshake Current Pre
Play clientbound
0x22 Chunk Data Current Pre
0x4E Entity Sound Effect Pre
0x4E 0x4F Player List Header And Footer Current (unchanged)
0x4F 0x50 Collect Item Current (unchanged)
0x50 0x51 Entity Teleport Current (unchanged)
0x51 0x52 Advancements Current (unchanged)
0x52 0x53 Entity Properties Current (unchanged)
0x53 0x54 Entity Effect Current (unchanged)
0x54 0x55 Declare Recipes Current (unchanged)
0x55 0x56 Tags Current Pre
0x57 Update Light Pre

New/modified data types

No changes so far.

Entity Metadata

Mobs

Entity IDs have shifted with the addition of some new mobs.

Block Actions

No changes so far.

Play

Clientbound

Chunk Data

Main article: Chunk Format
See also: #Unload Chunk

The server only sends skylight information for chunk pillars in the Overworld, it's up to the client to know in which dimenison 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).

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)
Ground-Up Continuous Boolean See Chunk Format
Primary Bit Mask VarInt Bitmask with bits 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 y=0 to y=15).
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.
Data structure

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. Sections are sent bottom-to-top, i.e. the first section, if sent, extends from Y=0 to Y=15.
Biomes Optional Int Array Only sent if Ground-Up Continuous is true; 256 entries if present
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, for lighting purposes. "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).
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 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 is given for each block with increasing x coordinates, within rows of increasing z coordinates, within layers of increasing y coordinates. For the half-byte light arrays, even-indexed items (those with an even x coordinate, starting at 0) are packed into the low bits, odd-indexed into the high bits.

Entity Sound Effect

Plays a sound effect from an entity.

Packet ID State Bound To Field Name Field Type Notes
0x4E Play Client Sound ID VarInt ID of hardcoded sound event (events as of 1.13.2)
Sound Category VarInt Enum The category that this sound will be played from (current categories)
Entity ID VarInt
Volume Float 1.0 is 100%, capped between 0.0 and 1.0 by Notchian clients
Pitch Float Float between 0.5 and 2.0 by Notchian clients

Tags

Packet ID State Bound To Field Name Field Type Notes
0x55 Play Client Block Tags (See below) IDs are block IDs
Item Tags (See below) IDs are item IDs
Fluid Tags (See below) IDs are fluid IDs
Entity Tags (See below) IDs are entity type IDs

Update Light

Updates light levels for a chunk.

Packet ID State Bound To Field Name Field Type Notes
0x57 Play Client Chunk X VarInt Chunk coordinate (block coordinate divided by 16, rounded down)
Chunk Z VarInt Chunk coordinate (block coordinate divided by 16, rounded down)
Sky Light Mask VarInt Mask containing 18 bits, with the lowest bit corresponding to chunk section -1 (in the void, y=-16 to y=-1) and the highest bit for chunk section 16 (above the world, y=256 to y=271)
Block Light Mask VarInt Mask containing 18 bits, with the same order as sky light
Sky Light arrays Array of arrays 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 arrays Array of arrays 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.

Individual block or sky light arrays are is given for each block with increasing x coordinates, within rows of increasing z coordinates, within layers of increasing y coordinates. Even-indexed items (those with an even x coordinate, starting at 0) are packed into the low bits, odd-indexed into the high bits.

Serverbound

No changes so far.

Handshaking

Clientbound

There are no clientbound packets in the Handshaking state, since the protocol immediately switches to a different state after the client sends the first packet.

Serverbound

Handshake

This causes the server to switch into the target state.

Packet ID State Bound To Field Name Field Type Notes
0x00 Handshaking Server Protocol Version VarInt See protocol version numbers (currently 404 441)
Server Address String Hostname or IP, e.g. localhost or 127.0.0.1, that was used to connect. The Notchian server does not use this information.
Server Port Unsigned Short Default is 25565. The Notchian server does not use this information.
Next State VarInt Enum 1 for status, 2 for login

Status

Clientbound

No changes so far.

Serverbound

No changes so far.

Login

Clientbound

No changes so far.

Serverbound

No changes so far.