Pre-release protocol

This page documents the changes from the last stable Minecraft release (currently 1.15.2, protocol 578) to the current pre-release (currently 20w20a, protocol 716). 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

The UUID type is now also sometimes encoded by the Notchian server as an array of four 32-bit integers, from most significant to least significant (matching the new format used on entity NBT). This representation is identical to using 16 bytes, two 64-bit integers, or one 128-bit integers.

Packets

ID	Packet name	Documentation
Handshaking serverbound
0x00	Handshake	Current	Pre
Play clientbound
0x22	Chunk Data	Current	Pre
0x26	Join Game	Current	Pre
0x3B	Respawn	Current	Pre
0x4E 0x43	Spawn Position	Current	(unchanged)
0x43 0x44	Display Scoreboard	Current	(unchanged)
0x44 0x45	Entity Metadata	Current	(unchanged)
0x45 0x46	Attach Entity	Current	(unchanged)
0x46 0x47	Entity Velocity	Current	(unchanged)
0x47 0x48	Entity Equipment	Current	(unchanged)
0x48 0x49	Set Experience	Current	(unchanged)
0x49 0x4A	Update Health	Current	(unchanged)
0x4A 0x4B	Scoreboard Objective	Current	(unchanged)
0x4B 0x4C	Set Passengers	Current	(unchanged)
0x4C 0x4D	Teams	Current	(unchanged)
0x4D 0x4E	Update Score	Current	(unchanged)
0x59	Entity Properties	Current	Pre
Play serverbound
0x0F	Generate Structure		Pre
0x0F 0x10	Keep Alive (serverbound)	Current	(unchanged)
0x10 0x11	Lock Difficulty	Current	(unchanged)
0x11 0x12	Player Position	Current	(unchanged)
0x12 0x13	Player Position And Rotation (serverbound)	Current	(unchanged)
0x13 0x14	Player Rotation	Current	(unchanged)
0x14 0x15	Player Movement	Current	(unchanged)
0x15 0x16	Vehicle Move (serverbound)	Current	(unchanged)
0x16 0x17	Steer Boat	Current	(unchanged)
0x17 0x18	Pick Item	Current	(unchanged)
0x18 0x19	Craft Recipe Request	Current	(unchanged)
0x19 0x1A	Player Abilities (serverbound)	Current	(unchanged)
0x1A 0x1B	Player Digging	Current	(unchanged)
0x1B 0x1C	Entity Action	Current	(unchanged)
0x1C 0x1D	Steer Vehicle	Current	(unchanged)
0x1D 0x1E	Recipe Book Data	Current	(unchanged)
0x1E 0x1F	Name Item	Current	(unchanged)
0x1F 0x20	Resource Pack Status	Current	(unchanged)
0x20 0x21	Advancement Tab	Current	(unchanged)
0x21 0x22	Select Trade	Current	(unchanged)
0x22 0x23	Set Beacon Effect	Current	(unchanged)
0x23 0x24	Held Item Change (serverbound)	Current	(unchanged)
0x24 0x25	Update Command Block	Current	(unchanged)
0x25 0x26	Update Command Block Minecart	Current	(unchanged)
0x26 0x27	Creative Inventory Action	Current	(unchanged)
0x27 0x28	Update Jigsaw Block	Current	Pre
0x28 0x29	Update Structure Block	Current	(unchanged)
0x29 0x2A	Update Sign	Current	(unchanged)
0x2A 0x2B	Animation (serverbound)	Current	(unchanged)
0x2B 0x2C	Spectate	Current	(unchanged)
0x2C 0x2D	Player Block Placement	Current	(unchanged)
0x2D 0x2E	Use Item	Current	(unchanged)
Login clientbound
0x02	Login Success	Current	Pre

New/modified data types

No changes so far.

Entity Metadata

FishingHook

Extends Entity.

Index	Type	Meaning		Default
7	VarInt	Hooked entity id + 1, or 0 if there is no hooked entity		0
8	Boolean	Is catchable		False

Abstract Arrow

Extends Entity.

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

Index	Type	Meaning		Default
7	Byte	Bit mask	Meaning	0
		0x01	Is critical
		0x02	Is noclip (used by loyalty tridents when returning)
8	OptUUID	Unused		Empty
9 8	Byte	Peircing level		0

Tipped Arrow

Extends Abstract 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
10 9	VarInt	Color (-1 for no particles)		-1

Spectral Arrow

Extends Abstract Arrow.

No additional metadata.

Trident

Extends Abstract Arrow.

Index	Type	Meaning		Default
10 9	VarInt	Loyalty level (enchantment)		0
11 10	Boolean	Has enchantment glint		False

Strider

Extends Animal.

Index	Type	Meaning		Default
16	VarInt	Total time to "boost" with warped fungus on a stick for		0
17	Boolean	Should display name tag (true unless riding a vehicle or on or in a block tagged with strider_warm_blocks (default: lava))		false
18	Boolean	Has saddle		false

Hoglin

Extends Animal.

Index	Type	Meaning		Default
16	Boolean	Is immune to zombification		false

Zoglin

Extends Monster.

Index	Type	Meaning		Default
15	Boolean	Is baby		false

Piglin

Extends Monster.

Index	Type	Meaning		Default
15	Boolean	Is baby		false
16	Boolean	Is immune to zombification		false
17	Boolean	Is charging crossbow		false

Zombie Pigman Zombified Piglin

Extends Zombie.

No additional metadata.

Block Actions

No changes so far.

Inventories

No changes so far.

Plugin Channels

No changes so far.

Play

Clientbound

Chunk Data

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 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 totaling 36 longs). 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	Optional array of Integer	1024 biome IDs, ordered by x then z then y, in 4×4×4 blocks. Not present if full chunk is false.
			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.

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.

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)
			Gamemode	Unsigned Byte	0: Survival, 1: Creative, 2: Adventure, 3: Spectator. Bit 3 (0x8) is the hardcore flag.
			Dimension	Int Enum	-1: Nether, 0: Overworld, 1: End; also, note that this is not a VarInt but instead a regular int.
			Hashed seed	Long	First 8 bytes of the SHA-256 hash of the world's seed.
			Max Players	Unsigned Byte	Was once used by the client to draw the player list, but now is ignored
			Level Type	String Enum (16)	default, flat, largeBiomes, amplified, customized, buffet, default_1_1
			View Distance	VarInt	Render distance (2-32)
			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	Further documentation needed.
			Is Flat	Boolean	Further documentation needed.

Respawn

To change the player's dimension (overworld/nether/end), send them a respawn packet with the appropriate dimension, followed by prechunks/chunks for the new dimension, and finally a position and look packet. You do not need to unload chunks, the client will do it automatically.

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x3B	Play	Client	Dimension	Int Enum	-1: The Nether, 0: The Overworld, 1: The End
			Hashed seed	Long	First 8 bytes of the SHA-256 hash of the world's seed.
			Gamemode	Unsigned Byte	0: survival, 1: creative, 2: adventure, 3: spectator. The hardcore flag is not included
			Level Type	String (16)	Same as Join Game
			Is Debug	Boolean	Further documentation needed.
			Is Flat	Boolean	Further documentation needed.
			Copy metadata	Boolean	If false, metadata is reset on the respawned player entity. Set to true for dimension changes (including the dimension change triggered by sending client status perform respawn to exit the end poem/credits), and false for normal respawns.

Avoid changing player's dimension to same dimension they were already in unless they are dead. If you change the dimension to one they are already in, weird bugs can occur, such as the player being unable to attack other players in new world (until they die and respawn).

If you must respawn a player in the same dimension without killing them, send two respawn packets, one to a different world and then another to the world you want. You do not need to complete the first respawn; it only matters that you send two packets.

Entity Properties

Sets attributes on the given entity.

Packet ID	State	Bound To	Field Name		Field Type		Notes
0x59	Play	Client	Entity ID		VarInt
			Number Of Properties		Int		Number of elements in the following array
			Property	Key	Array	String (64) Identifier	See below
				Value		Double	See below
				Number Of Modifiers		VarInt	Number of elements in the following array
				Modifiers		Array of Modifier Data	See Attribute#Modifiers. Modifier Data defined below.

Known Key values (see also Attribute#Modifiers):

Key	Default	Min	Max	Label
generic.maxHealth generic.max_health	20.0	0.0	1024.0	Max Health
generic.followRange generic.follow_range	32.0	0.0	2048.0	Follow Range
generic.knockbackResistance generic.knockback_resistance	0.0	0.0	1.0	Knockback Resistance
generic.movementSpeed generic.movement_speed	0.7	0.0	1024.0	Movement Speed
generic.attackDamage generic.attack_damage	2.0	0.0	2048.0	Attack Damage
generic.attackSpeed generic.attack_speed	4.0	0.0	1024.0	Attack Speed
generic.flyingSpeed generic.flying_speed	0.4	0.0	1024.0	Flying Speed
generic.armor	0.0	0.0	30.0	Armor
generic.armorToughness generic.armor_toughness	0.0	0.0	20.0	Armor Toughness
generic.attackKnockback generic.attack_knockback	0.0	0.0	5.0	—
generic.luck	0.0	-1024.0	1024.0	Luck
horse.jumpStrength horse.jump_strength	0.7	0.0	2.0	Jump Strength
zombie.spawnReinforcements zombie.spawn_reinforcements	0.0	0.0	1.0	Spawn Reinforcements Chance
generic.reachDistance	5.0	0.0	1024.0	Player Reach Distance (Forge only)
forge.swimSpeed	1.0	0.0	1024.0	Swimming Speed (Forge only)

Unknown attributes will cause a game crash (MC-150405) due to the default minimum being larger than the default value.

Modifier Data structure:

Field Name	Field Type	Notes
UUID	UUID
Amount	Double	May be positive or negative
Operation	Byte	See below

The operation controls how the base value of the modifier is changed.

• 0: Add/subtract amount
• 1: Add/subtract amount percent of the current value
• 2: Multiply by amount percent

All of the 0's are applied first, and then the 1's, and then the 2's.

Serverbound

Generate Structure

Sent when Generate is pressed on the Jigsaw Block interface.

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x0F	Play	Server	Location	Position	Block entity location
			Levels	VarInt	Value of the levels slider/max depth to generate

Update Jigsaw Block

Sent when Done is pressed on the Jigsaw Block interface.

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x27 0x28	Play	Server	Location	Position	Block entity location
			Attachment type	Identifier
			Name	Identifier
			Target	Identifier
			Target pool Pool	Identifier
			Final state	String	"Turns into" on the GUI, final_state in NBT
			Joint type	String	rollable if the attached piece can be rotated, else aligned

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 578 716)
			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. Note that SRV records are a complete redirect, e.g. if _minecraft._tcp.example.com points to mc.example.org, users connecting to example.com will provide mc.example.org as server address in addition to connecting to it.
			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

Login Success

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x02	Login	Client	UUID	String (36) UUID	Unlike in other packets, this field contains the UUID as a string with hyphens.
			Username	String (16)

This packet switches the connection state to play.

Serverbound

No changes so far.