Pre-release protocol

Revision as of 18:48, 22 April 2020 by Pokechu22 (talk | contribs) (Chunk data was changed)
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This page documents the changes from the last stable Minecraft release (currently 1.15.2, protocol 578) to the current pre-release (currently 20w17a, protocol 713). 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.


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.


ID Packet name Documentation
Handshaking serverbound
0x00 Handshake Current Pre
Play clientbound
0x22 Chunk Data 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


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.


Extends Abstract Arrow.

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


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


Extends Animal.

Index Type Meaning Default
16 Boolean Is immune to zombification false


Extends Monster.

Index Type Meaning Default
15 Boolean Is baby false


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.


No changes so far.

Plugin Channels

No changes so far.



Chunk Data

Main article: Chunk Format
See also: #Unload Chunk
Huh.png 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.

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
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.


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



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.



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 578 713)
Server Address String Hostname or IP, e.g. localhost or, that was used to connect. The Notchian server does not use this information. Note that SRV records are a complete redirect, e.g. if points to, users connecting to will provide 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



No changes so far.


No changes so far.



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.


No changes so far.