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 18w45a, protocol 444). 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

Position

64-bit value split in to three parts

  • x: 26 MSBs
  • z: 26 LSBs middle bits
  • y: 12 bits between them LSBs

Encoded as followed:

((x & 0x3FFFFFF) << 38) | ((y & 0xFFF) << 26) | (z & 0x3FFFFFF) ((z & 0x3FFFFFF) << 12) | (y & 0xFFF)

And decoded as:

val = read_unsigned_long();
x = val >> 38;
y = (val >> 26) & 0xFFF val & 0xFFF;
z = val << 38 >> 38 (val << 38 >> 38) >> 12;

Note: The details of bit shifting are rather language dependent; the above may work in Java but probably won't in other languages without some tweaking. In particular, you will usually receive positive numbers even if the actual coordinates are negative. This can be fixed by adding something like the following:

if x >= 2^25 { x -= 2^26 }
if y >= 2^11 { y -= 2^12 }
if z >= 2^25 { z -= 2^26 }

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.

Arrow

Extends Entity.

Abstract base class for TippedArrow (which is used for regular arrows as well as tipped ones) and Spectral Arrow.

Index Type Meaning Default
6 Byte Bit mask Meaning 0
0x01 Is critical
0x02 Is noclip (used by loyalty tridents when returning)
7 OptUUID Shooter UUID Empty
8 Byte Piercing level 0

TippedArrow

Extends Arrow.

Used for both tipped and regular arrows. If not tipped, then color is set to -1 and no tipped arrow particles are used.

Index Type Meaning Default
8 9 VarInt Color (-1 for no particles) -1

Trident

Extends Arrow.

Index Type Meaning Default
8 9 VarInt Loyalty level (enchantment) 0

Fireworks

Extends Entity.

Index Type Meaning Default
6 Slot Firework info empty
7 VarInt Entity ID of entity which used firework (for elytra boosting) 0
8 Boolean Shot at angle (from a crossbow) false

Panda

Extends Animal.

Index Type Meaning Default
13 Integer Breed timer? Set to 32 when something happens, and then counts down to 0 again. At 29 and 14 (before counting down), will play the entity.panda.cant_breed sound event. 0
14 Integer Sneeze timer. Counts up from 0; when it hits 1 the entity.panda.pre_sneeze event plays and when it hits 21 the entity.panda.sneeze event plays (and it is set back to 0 and the sneeze flag is cleared). 0
15 Integer Eat timer. If nonzero, counts upwards. 0
16 Byte Main Gene 0
17 Byte Hidden Gene 0
18 Byte Bit mask Meaning 0
0x01 Unused
0x02 Is sneezing
0x04 Is eating
0x08 Unknown
0x10 Unknown

Pillager

Extends Abstract Illlager.

Index Type Meaning Default
13 Boolean Using crossbow false

Ocelot

Extends TameableAnimal Ageable.

Index Type Meaning Default
15 VarInt Type (0 = untamed, 1 = tuxedo, 2 = tabby, 3 = siamese). Used to render regardless as to whether it is tamed or not. 0
13 Boolean Is trusting false

Cat

Extends TameableAnimal.

Index Type Meaning Default
15 VarInt Type (0 = tabby, 1 = black, 2 = red, 3 = siamese, 4 = british_shorthair, 5 = calico, 6 = persian, 7 = ragdoll, 8 = white, 9 = all_black) 1
16 Boolean Unknown false
17 Boolean Unknown false
18 VarInt Collar color (values are those used with dyes) 14 (Red)

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).
Unknown NBT Possibly heightmap-related?
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 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 0x56 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
Empty Sky Light Mask VarInt Mask containing 18 bits, which indicates sections that have 0 for all their sky light values. If a section is set in both this mask and the main sky light mask, it is ignored for this mask and it is included in the sky light arrays. If it is only set in this mask, it is _not_ included in the sky light arrays.
Empty Block Light Mask VarInt Mask containing 18 bits. However, this seems to be written into incorrectly, and is always 0; instead block light values are put into the sky light mask. (MC-138918)
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 404 444)
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.