Pre-release protocol

Jump to navigation Jump to search

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

Tab-complete (0xCB)


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 int 0 0-3 for 'far', 'normal', 'short', 'tiny'.
Chat info byte Bits: 0: chat enabled, 2: colors enabled
Unknown byte 0 First three bits(bitmask 0x7) are used as int, bit four(bitmask 0x8) is used as bool
Total Size: 8 bytes + length of string

Encryption Key Response (0xFC)


Sent by the client after receiving 0xFD. The server responds with 0xFC, too (but with an empty Shared key).

The shared key is a client-generated, 16 bytes long key for RC4 encryption. The key is encrypted with RSA with the public key from the Encryption Key Request packet.

Packet ID Field Name Field Type Example Notes
0xFC Shared key length short
Shared key byte array
Total Size: 3 bytes + length of key

Encryption Key Request (0xFD)

Server to client

Sent after handshakes.

Public key encryption: RSA.

Packet ID Field Name Field Type Example Notes
0xFD Server id string
Public key length short
Public key byte array
Total Size: 5 bytes + length of string + length of key

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
Unknown byte 9
Unknown byte 63
Total Size: 17 bytes + length of string

Changed packets

Login Request (0x01)


Just a guess: stripped unused string field.

Client to Server

Packet ID Field Name Field Type Example Notes
0x01 This packet is sent by the client and empty
Total Size: 1 byte

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 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

Hanshake (0x02)

Client to server only - before encryption, not sure what happens thereafter, may still be a server reply --Ceiru 23:12, 27 April 2012 (MST)

Packet ID Field Name Field Type Example Notes
0x02 Protocol Version byte 31
Username and Host string TkTech The username of the player attempting to connect, and the host he is connecting to, seperated by a semicolon.
Server Host string localhost
Server Port int 25565
Total Size: 10 bytes + length of strings

Protocol History


  • 12w18a
  • New packet: 0x3D Name Sound Effect
  • Changed packet: 0x01 Login Request
  • Changed packet: 0x02 Handhshake
  • Changed packet: 0xCA Player Abilities
  • Changed packet: 0xCC Player Settings
  • 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


  • 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
  • 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


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