Pre-release protocol

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)

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	int	0	0-3 for 'far', 'normal', 'short', 'tiny'.
	Chat info	byte	Bits: 0: chat enabled, 2: colors enabled
Total Size:	7 bytes + length of string

Encryption Key Response (0xFC)

Two-Way

Sent after receiving 0xFD. After the client send a Encryption Key Response packet to the server the server responds with one too(with a 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

Changed packets

Login Request (0x01)

Two-Way

Just a guess: stripped unused string field.

Client to Server

Packet ID	Field Name	Field Type	Example	Notes
0x01	Protocol Version	int	20	1.2.5's protocol version is 29
	Username	string	TkTech	The name of the user attempting to login, max length of 16
	Not used	int	0
	Not used	int	0
	Not used	byte	0
	Not used	unsigned byte	0
	Not used	unsigned byte	0
Total Size:	20 bytes + length of strings

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	int	0	0 for survival, 1 for creative
	Dimension	int	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:	20 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.
Total Size:	4 bytes + length of string

Protocol History

2012-04-26

• 12w17a
• Protocol version is now 31
• After exchanging handshakes, RC4 based encryption is initiated. The server sends 0xFD, which is replied by the client using 0xFC.
• 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

2012-04-19

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