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 18w50a, protocol 451). 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
0x09 Update Block Entity Current Pre
0x22 Chunk Data Current Pre
0x2C Open Book Pre
0x2C 0x2D Open Sign Editor Current (unchanged)
0x2D 0x2E Craft Recipe Response Current (unchanged)
0x2E 0x2F Player Abilities (clientbound) Current (unchanged)
0x2F 0x30 Combat Event Current (unchanged)
0x30 0x31 Player List Item Current (unchanged)
0x31 0x32 Face Player Current (unchanged)
0x32 0x33 Player Position And Look (clientbound) Current (unchanged)
0x33 0x34 Use Bed Current (unchanged)
0x34 0x35 Unlock Recipes Current (unchanged)
0x35 0x36 Destroy Entities Current (unchanged)
0x36 0x37 Remove Entity Effect Current (unchanged)
0x37 0x38 Resource Pack Send Current (unchanged)
0x38 0x39 Respawn Current (unchanged)
0x39 0x3A Entity Head Look Current (unchanged)
0x3A 0x3B Select Advancement Tab Current (unchanged)
0x3B 0x3C World Border Current (unchanged)
0x3C 0x3D Camera Current (unchanged)
0x3D 0x3E Held Item Change (clientbound) Current (unchanged)
0x3E 0x3F Display Scoreboard Current (unchanged)
0x3F 0x40 Entity Metadata Current (unchanged)
0x40 0x41 Attach Entity Current (unchanged)
0x41 0x42 Entity Velocity Current (unchanged)
0x42 0x43 Entity Equipment Current (unchanged)
0x43 0x44 Set Experience Current (unchanged)
0x44 0x45 Update Health Current (unchanged)
0x45 0x46 Scoreboard Objective Current (unchanged)
0x46 0x47 Set Passengers Current (unchanged)
0x47 0x48 Teams Current (unchanged)
0x48 0x49 Update Score Current (unchanged)
0x49 0x4A Spawn Position Current (unchanged)
0x4A 0x4B Time Update Current (unchanged)
0x4B 0x4C Title Current (unchanged)
0x4C 0x4D Stop Sound Current (unchanged)
0x4D 0x4E Sound Effect Current (unchanged)
0x4F Entity Sound Effect Pre
0x4E 0x50 Player List Header And Footer Current (unchanged)
0x4F 0x51 Collect Item Current (unchanged)
0x50 0x52 Entity Teleport Current (unchanged)
0x51 0x53 Advancements Current (unchanged)
0x52 0x54 Entity Properties Current (unchanged)
0x53 0x55 Entity Effect Current (unchanged)
0x54 0x56 Declare Recipes Current (unchanged)
0x55 0x57 Tags Current Pre
0x58 Update Light Pre
Play serverbound
0x1B Recipe Book Data Current Pre

New/modified data types

No changes so far.

Entity Metadata

Entity Metadata Format

Note that entity metadata is a totally distinct concept from block metadata. It is not required to send all metadata fields, or even any metadata fields, so long as the terminating entry is correctly sent.

Entity Metadata is an array of entries, each of which looks like the following:

Name Type Meaning
Index Unsigned Byte Unique index key determining the meaning of the following value, see the table below. If this is 0xff then the it is the end of the Entity Metadata array and no more is read.
Type Optional VarInt Enum Only if Index is not 0xff; the type of the index, see the table below
Value Optional value of Type Only if Index is not 0xff: the value of the metadata field
Value of Type field Type of Value field Notes
0 Byte
1 VarInt
2 Float
3 String
4 Chat
5 OptChat (Boolean + Optional Chat) Chat is present if the Boolean is set to true
6 Slot
7 Boolean
8 Rotation 3 floats: rotation on x, rotation on y, rotation on z
9 Position
10 OptPosition (Boolean + Optional Position) Position is present if the Boolean is set to true
11 Direction (VarInt) (Down = 0, Up = 1, North = 2, South = 3, West = 4, East = 5)
12 OptUUID (Boolean + Optional UUID) UUID is present if the Boolean is set to true
13 OptBlockID (VarInt) 0 for absent otherwise, id << 4 | data
14 NBT
15 Particle
16 Villager Data 3 VarInts: villager type, villager profession, level

Villager type (minecraft:villager_type registry):

Name ID
minecraft:desert 0
minecraft:jungle 1
minecraft:plains 2
minecraft:savanna 3
minecraft:snow 4
minecraft:swamp 5
minecraft:taiga 6

Villager professions (minecraft:villager_profession registry):

Name ID
minecraft:none 0
minecraft:armorer 1
minecraft:butcher 2
minecraft:cartographer 3
minecraft:cleric 4
minecraft:farmer 5
minecraft:fisherman 6
minecraft:fletcher 7
minecraft:leatherworker 8
minecraft:librarian 9
minecraft:mason 10
minecraft:nitwit 11
minecraft:shepherd 12
minecraft:toolsmith 13
minecraft:weaponsmith 14

Mobs

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

Itemed Throwable

Extends Throwable.

Used for all things that previously extended throwable other than potions, which already had an item.

Index Type Meaning Default
6 Slot Item empty (which behaves as if it were a specific item, depending on the subclass)

Egg

Extends Throwable.

No additional metadata.

An empty item behaves as if the item were a minecraft:egg.

Ender Pearl

Extends Throwable.

No additional metadata.

An empty item behaves as if the item were a minecraft:ender_pearl.

Experience Bottle

Extends Throwable.

No additional metadata.

minecraft:experience_bottle

Snowball

Extends Throwable.

No additional metadata.

minecraft:snowball

Eye of Ender

Extends Entity.

Index Type Meaning Default
6 Slot Item empty (which behaves as if it were a minecraft:ender_eye)

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

Itemed Fireball

Extends Entity.

Used for regular and small fireballs. Not used for dragon fireballs and wither skulls. Interestingly, regular fireballs do not come from an item.

Index Type Meaning Default
6 Slot Item empty (which behaves as if it were a minecraft:fire_charge)

Fireball

Extends Abstract Fireball Itemed Fireball. This is the large fireball shot by ghasts.

No additional metadata.

Small Fireball

Extends Abstract Fireball Itemed Fireball. This is the fireball shot by blazes and dispensers with fire charges.

No additional metadata.

Fireworks

Extends Entity.

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

Illager Beast

Extends Monster

No additional metadata.

Status Description
4 Starts the attack animation.
39 Starts the stun animation.

Giant Zombie

Extends Monster Zombie.

No additional metadata.

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
Status Description
40 Spawn smoke particles (trust gaining failed)
41 Spawn heart particles (trust gaining succeeded)

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)

Villager

Extends Ageable.

Index Type Meaning Default
13 VarInt Villager Data Villager Data 0 Plains/None/1

Zombie Villager

Extends Zombie.

Index Type Meaning Default
16 Boolean Is converting false
17 VarInt Villager Data Profession Villager Data 0 Plains/None/1

Block Actions

No changes so far.

Plugin Channels

minecraft:book_open

Server to client

When a player right clicks with a signed book. This tells the client to open the book GUI.

The payload is a VarInt enum for the selected hand: 0 for the main hand, 1 for the offhand.

Replaced with Open Book packet.

Play

Clientbound

Update Block Entity

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

Packet ID State Bound To Field Name Field Type Notes
0x09 Play Client Location Position
Action Unsigned Byte The type of update to perform, see below
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)

Action field:

  • 1: Set data of a mob spawner (everything except for SpawnPotentials: current delay, min/max delay, mob to be spawned, spawn count, spawn range, etc.)
  • 2: Set command block text (command and last execution status)
  • 3: Set the level, primary, and secondary powers of a beacon
  • 4: Set rotation and skin of mob head
  • 5: Declare a conduit
  • 6: Set base color and patterns on a banner
  • 7: Set the data for a Structure tile entity
  • 8: Set the destination for a end gateway
  • 9: Set the text on a sign
  • 10: Declare a shulker box, no data appears to be sent and the client seems to do fine without this packet. Perhaps it is a leftover from earlier versions?
  • 11: Declare a bed
  • 12: Set data of a jigsaw block

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)
Full chunk 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).
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).
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.

Open Book

Sent when a player right clicks with a signed book. This tells the client to open the book GUI.

Packet ID State Bound To Field Name Field Type Notes
0x2C Play Client Hand VarInt enum 0: Main hand, 1: Off hand

Entity Sound Effect

Plays a sound effect from an entity.

Packet ID State Bound To Field Name Field Type Notes
0x4F Play Client Sound ID VarInt ID of hardcoded sound event (events as of 18w48a)
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 0x57 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
0x58 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 (the notchian server does not create such masks). 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, which indicates sections that have 0 for all their block light values. If a section is set in both this mask and the main block light mask, it is ignored for this mask and it is included in the block light arrays (the notchian server does not create such masks). If it is only set in this mask, it is not included in the block light arrays.
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

Recipe Book Data

Packet ID State Bound To Field Name Field Type Notes
0x1B Play Server Type VarInt Determines the format of the rest of the packet
Type Field Name
0: Displayed Recipe Recipe ID Identifier A recipe ID
1: Recipe Book States Crafting Recipe Book Open Boolean Whether the player has the crafting recipe book currently opened/active.
Crafting Recipe Filter Active Boolean Whether the player has the crafting recipe book filter option currently active.
Smelting Recipe Book Open Boolean Whether the player has the smelting recipe book currently opened/active.
Smelting Recipe Filter Active Boolean Whether the player has the smelting recipe book filter option currently active.
Blasting Recipe Book Open Boolean May be swapped with smoking recipe book. Also, the notchian client appears to use the same value for both of those books currently.
Blasting Recipe Filter Active Boolean May be swapped with smoking recipe book. Also, the notchian client appears to use the same value for both of those books currently.
Smoking Recipe Book Open Boolean
Smoking Recipe Filter Active Boolean

The Recipe Book Status type is sent when one of the states changes.

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 404 451)
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.