Pre-release protocol

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This page documents the changes from the last stable Minecraft release (currently 1.2.5) to the current pre-release (or weekly release).

New packets

Map Chunk Bulk (0x38)

To reduce the number of bytes this packet is used to send chunk columns together for better compression results. The packet contains up to 100 chunk columns (later this might be reduced to 50).

The data part is a zlib compressed byte array containing the chunk data. The meta data part specifies which chunks in which order the data part exists of.

To split this packet into chunks you need to uncompress the data array. Then you can iterate through the data part. Each part is 10240 * n + 256 bytes. n is the number of chunks in the current chunk column(this is the number of flags set in the primary bitmap). 10240 is the amount of bytes for each chunk without add bitmap, 256 bytes are used for biomes. The second short in the meta data part is not yet in use. It could specify if the chunk uses the add bitmap part, because it has very high block ids, but not in the current snapshot.

Packet ID Field Name Field Type Example Notes
0x38 Chunk Column Count short The number of chunk columns in this packet
Chunk data size int the size of the data field
Data byte array compressed chunk data
meta information chunk bulk meta information Chunk column count times the Meta information structure (See notes for details)
Total Size: 7 + (Chunk data size) + 12 * (Chunk Column Count) bytes


Chunk Bulk Meta Information Structure

Field Name Field Type Example Notes
Chunk Column X int 10 The X coordinate of the specific chunk column
Chunk Column Z int 10 The Z coordinate of the specific chunk column
Chunk Primary bitmap short 15 A bitmap which specifies which chunk is not empty in this chunk column
Chunk Add bitmap? short 0 A bitmap which specifies which chunk need add information because of very high block ids. not yet used. needs verification
Total Size: 12 bytes


Tab-complete (0xCB)

Two-way

Sent C->S when the user presses [tab] while writing text. The payload contains all text behind the cursor.

The server responds with an auto-completion of the last word sent to it. In the case of regular chat, this is a player username. Command names and parameters are also supported.

In the event of more than one possible completion, the server responds with the options packed into the single string field, separated by a null character. Note that as strings are UTF-16, this is two bytes wide.

Packet ID Field Name Field Type Example Notes
0xCB Text string
Total Size: 3 bytes + length of string

Locale and View Distance (0xCC)

Client to server

Sent when the player connects, or when settings are changed.

Packet ID Field Name Field Type Example Notes
0xCC Locale string en_GB
View distance byte 0 0-3 for 'far', 'normal', 'short', 'tiny'.
Chat flags byte 8 Chat settings. See notes below.
Difficulty byte 0 Client-side difficulty from options.txt
Total Size: 8 bytes + length of string

Chat flags has several values packed into one byte.

Chat Enabled: Bits 0-1. 00: Enabled. 01: Commands only. 10: Hidden.

Colors Enabled: Bit 3. 0: Disabled. 1: Enabled.

Client Statuses (0xCD)

Client to server

Sent when the client is ready to complete login and when the client is ready to respawn after death.

Packet ID Field Name Field Type Example Notes
0xCD Payload byte 0 Bit field. 0: Initial spawn, 1: Respawn after death
Total Size: 2 bytes

Encryption Key Response (0xFC)

Two-Way

See Protocol Encryption for information on this packet.

Packet ID Field Name Field Type Example Notes
0xFC Shared secret length short
Shared secret byte array
Verify token length short
Verify token response byte array
Total Size: 5 bytes + length of shared secret + length of token

Encryption Key Request (0xFD)

Server to client

See Protocol Encryption for information on this packet.

Packet ID Field Name Field Type Example Notes
0xFD Server id string
Public key length short
Public key byte array
Verify token length short
Verify token byte array
Total Size: 7 bytes + length of string + length of key + length of token



Named Sound Effect (0x3E)

Server to client

Used to play a sound effect on the client.

Packet ID Field Name Field Type Example Notes
0x3E Sound name string step.grass 250
Effect position X int 250 effect X multiplied by 8
Effect position Y int 250 effect Y multiplied with 8
Effect position Z int 250 effect Z multiplied with 8
Volume float 9 1 is 100%, can be more
Pitch byte 1 63 is 100%, can be more
Total Size: 20 bytes + length of string

Block Break Animation (0x37)

Packet ID Field Name Field Type Example Notes
0x37 EID? int Entity breaking the block?
X int Block position
Y int
Z int
Unknown byte 1 ?
Total Size: 4 bytes

Changed packets

Login Request (0x01)

Two-Way

See Protocol Encryption for information on logging in.

Client to Server

Just 1 byte C->S

Packet ID
0x01

Server to Client

Packet ID Field Name Field Type Example Notes
0x01 Entity ID int 1298 The Players Entity ID
Level Type string default default or SUPERFLAT; level-type in server.properties
Server mode byte 0 0 for survival, 1 for creative
Dimension byte 0 -1: The Nether, 0: The Overworld, 1: The End
Difficulty byte 1 0 thru 3 for Peaceful, Easy, Normal, Hard
Not used unsigned byte 0 Only 0 observed from vanilla server, was previously world height
Max players unsigned byte 8 Used by the client to draw the player list
Total Size: 12 bytes + length of strings

Handshake (0x02)

Client to server

See Protocol Encryption for information on logging in.

Packet ID Field Name Field Type Example Notes
0x02 Protocol Version byte 38
Username string TkTech The username of the player attempting to connect
Server Host string localhost
Server Port int 25565
Total Size: 10 bytes + length of strings

Entity Equipment (0x05)

Server to Client

Packet ID Field Name Field Type Example Notes
0x05 Entity ID int 0x00010643 Named Entity ID
Slot short 4 Equipment slot: 0=held, 1-4=armor slot
Item slot Item in slot format
Total Size: 11 bytes

Respawn (0x09)

Two-Way

Sent by the client when the player presses the "Respawn" button after dying. The server then teleports the user to the spawn point, and sends a respawn packet in response. The client will not leave the respawn screen until it receives a respawn packet.

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.

Client to Server

Packet ID
0x09

Server to Client

Packet ID Field Name Field Type Example Notes
0x09 Dimension int 1 -1: The Nether, 0: The Overworld, 1: The End
Difficulty byte 1 0 thru 3 for Peaceful, Easy, Normal, Hard. 1 is always sent c->s
Creative mode byte 1 0 for survival, 1 for creative.
World height short 256 Defaults to 256
Level Type string default See 0x01 login
Total Size: 11 bytes + length of string

Spawn Named Entity (0x14)

Server to Client

Packet ID Field Name Field Type Example Notes
0x14 EID int 94453 Player ID
Player Name string Twdtwd Max length of 16
X int 784 Player X as Absolute Integer
Y int 2131 Player Y as Absolute Integer
Z int -752 Player Z as Absolute Integer
Yaw byte 0 Player rotation as a packed byte
Pitch byte 0 Player rotation as a packed byte
Current Item short 0 The item the player is currently holding. Note that this should be 0 for "no item", unlike -1 used in other packets. A negative value crashes clients.
Metadata Metadata 127
Unknown Byte
Total Size: 23 bytes + length of strings + metadata (at least 1)

Spawn Object/Vehicle (0x17)

Server to Client

Sent by the server when an Object/Vehicle is created. The throwers entity id is now used for fishing floats too.

Packet ID Field Name Field Type Example Notes
0x17 EID int 62 Entity ID of the Object
Type byte 11 The type of object (see Entities#Objects)
X int 16080 The Absolute Integer X Position of the object
Y int 2299 The Absolute Integer Y Position of the object
Z int 592 The Absolute Integer Z Position of the object
thrower's entity ID int 0 If this is bigger than 0, this is a entity trown by a other entity and the next 3 fields are sent.
Speed X short 0 Not sent if the thrower entity ID is 0. The speed of this entity along the X axis.
Speed Y short 0 Not sent if the thrower entity ID is 0. The speed of this entity along the Y axis.
Speed Z short 0 Not sent if the thrower entity ID is 0. The speed of this entity along the Z axis.
Total Size: 22 or 28 bytes


Spawn Mob (0x18)

Server to Client

Sent by the server when a Mob Entity is Spawned

Packet ID Field Name Field Type Example Notes
0x18 EID int 446 Entity ID
Type byte 91 The type of mob. See Entities#Mobs
X int 13366 The Absolute Integer X Position of the object
Y int 2176 The Absolute Integer Y Position of the object
Z int 1680 The Absolute Integer Z Position of the object
Yaw byte -27 The yaw in steps of 2p/256
Pitch byte 0 The pitch in steps of 2p/256
Head Yaw byte Head yaw in steps of 2p/256
Velocity Z short 0
Velocity X short 0
Velocity Y short 0
Metadata Metadata 127 Varies by mob, see Entities
Total Size: 27 bytes + Metadata (at least 1)


Destroy Entity (0x1D)

Server to Client

Sent by the server when an list of Entities is to be destroyed on the client.

Packet ID Field Name Field Type Example Notes
0x1D Entity Count byte 3 The amount of entities which should be destroyed
Entity IDs array of int 452, 546, 123 The list of entity ids which should be destroyed
Total Size: 2 + (entity count * 4) bytes


Chunk Data (0x33)

Server to Client

See also: Map Format

Chunks are sent a column at a time, with some sections optionally missing from each packet (those consisting only of air).

Packet ID Field Name Field Type Example Notes
0x33 X int Chunk X Coordinate (*16 to get true X)
Z int Chunk Z Coordinate (*16 to get true Z)
Ground-up continuous boolean This is True if the packet represents all sections in this vertical column, where the primary bit map specifies exactly which sections are included, and which are air.
Primary bit map unsigned short 15 Bitmask with 1 for every 16x16x16 section which data follows in the compressed data.
Add bit map unsigned short 0 Same as above, but this is used exclusively for the 'add' portion of the payload
Compressed size int Size of compressed chunk data.
Compressed data unsigned byte array … The chunk data is compressed using ZLib Deflate function.
Total Size: 22 bytes + Compressed chunk size


Block Change (0x35)

Server to Client

Packet ID Field Name Field Type Example Notes
0x35 X int 502 Block X Coordinate
Y byte 71 Block Y Coordinate
Z int 18 Block Z Coordinate
Block Type short 78 The new block type for the block
Block Metadata byte 0 The new Metadata for the block
Total Size: 13 bytes

Block Action (0x36)

Server to Client

This packet is used for a number of things:

  • Chests opening and closing
  • Pistons pushing and pulling
  • Note blocks playing
Packet ID Field Name Field Type Example Notes
0x36 X int 502 Block X Coordinate
Y short 71 Block Y Coordinate
Z int 18 Block Z Coordinate
Byte 1 byte 3 Varies depending on block - see below
Byte 2 byte 17 Varies depending on block - see below
Block ID byte 29 The block id this action is set for
Total Size: 13 bytes

See Also: Block Actions

Explosion (0x3C)

Server to Client

Sent when an explosion occurs (creepers, TNT, and ghast fireballs).

Packet ID Field Name Field Type Example Notes
0x3C X double
Y double
Z double
Radius float 3.0 Currently unused in the client
Record count int This is the count, not the size. The size is 3 times this value.
Records (byte, byte, byte) × count Each record is 3 bytes, which seem to be XYZ offsets of affected blocks.
Unknown float
Unknown float
Unknown float
Total Size: 45 bytes + 3*(Record count) bytes


Player Abilities (0xCA)

This packet has now been compressed into 3 bytes. The latter 2 bytes are used to indicate the walking and flying sppeds respectively, while the first byte is used to determine the value of 4 booleans.

These booleans are whether damage is disabled (god mode), whether the player is flying, whether the player can fly, and whether the player is in creative mode.

To get the values of these booleans, simply AND (&) the byte with 1,2,4 and 8 respectively, to get the 0 or 1 bitwise value. To set them OR (|) them with their repspective masks.

Packet ID Field Name Field Type Example Notes
0xCA Flags byte 5
Flying speed byte 12
Walking speed byte 25
Total Size: 4 bytes

Player Block Placement (0x0F)

Packet ID Field Name Field Type Example Notes
0x0F X int 32 Block position
Y unsigned byte 64 Block position
Z int 32 Block position
Direction byte 3 The offset to use for block/item placement (see below)
Held item slot
Unknown byte 0 - 0x0B (or more) ?
Unknown byte 0 - 0x10 ?
Unknown byte 0 - 0x10 ?
Total Size: 11 bytes + slot data

Removed packets

Chunk Allocation Packet (0x32)

The chunk Allocation Packet is not longer in use. Memory will automatically allocated with a incoming Map Chunk packet. To deallocate memory you need to send a MapChunk packet, which only contains biome data for plains(all biome bytes set to 1). So the Add and Primary bitmap must set to 0, and Ground-up continuous to true. Because the payload of this packet is compressed and static you can use a hardcoded value for it, so you don't need to compress it each time.

This is the payload which is used in the Compressed Data part to deallocate a chunk column:

0x78, 0x9C, 0x63, 0x64, 0x1C, 0xD9, 0x00, 0x00, 0x81, 0x80, 0x01, 0x01

Protocol History

2012-07-23

  • 12w30a
  • Protocol version is still 38
  • Changed packets 0x14 and 0x35

2012-07-05

  • 12w27a
  • Protocol version is now 38
  • Added packet 0x38

2012-06-21

  • 12w25a
  • Packet 0xFC and 0xFD include a 4 byte long byte array. This is hashed with the public RSA key and sent back. See Protocol Encryption for further info.
  • Packet 0x3E changed to include float rather than byte.

2012-06-14

  • 12w24a
  • Protocol version is now 36
  • Changed Packet 0x01(Login Request), only used as Login Reply
  • New Packet 0xCD used for Login Request and Respawn (1 byte payload)
  • All items (except the empty hand) now send enchantment data

2012-06-07

  • 12w23b
  • Protocol version is now 35
  • Change packet: Player Block Placement
  • New Packet: Block breaking animation

2012-05-24

  • 12w21a
  • No packet changes but the algorithm was changed to AES128 with the shared key as the IV, will be described in Protocol Encryption

2012-05-10

  • 12w19a
  • No packet changes, but an other encryption algorythm is used, described in Protocol Encryption
  • The items which are not enchantable in 12w18a are now readded
  • Fishing floats, spawned by a 0x17 packet do now use the extra fields

2012-05-03

  • 12w18a
  • Protocol version is now 32
  • New packet: 0x3D Name Sound Effect
  • Changed packet: 0x01 Login Request
  • Changed packet: 0x02 Handshake
  • Changed packet: 0xCA Player Abilities
  • Changed packet: 0xCC Locale and View Distance
  • Changed packet: 0x09 Respawn
  • Removed packet: 0x32 Map Column Allocation
  • This items are not enchantable in this version: 0x103, 0x105, 0x15A, 0x167, 0x10C, 0x10D, 0x10E, 0x10F, 0x122, 0x110, 0x111, 0x112, 0x113, 0x123, 0x10B, 0x100, 0x101, 0x102, 0x124, 0x114, 0x115, 0x116, 0x117, 0x125, 0x11B, 0x11C, 0x11D, 0x11E, 0x126

2012-04-26

  • 12w17a
  • Protocol version is now 31
  • RC4 based encryption, described in Protocol Encryption
  • Changed packet: 0x01 Login Request
  • Changed packet: 0x02 Handshake
  • Changed packet: 0xCC Locale and View Distance
  • Changed packet: 0xCA Player Abilities
  • New packet: 0xFC Encryption Key Response
  • New packet: 0xFD Encryption Key Request
  • New Item: Book & Quills (0x182) is enchantable
  • New Item: Written Book (0x183) is enchantable

2012-04-19

  • 12w16a
  • Protocol version is now 30
  • New packet: 0xCB Tab-complete
  • New packet: 0xCC Locale and View Distance
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