Pre-release protocol

This page documents the changes from the last stable Minecraft release (currently 1.0.1) to the current pre-release (currently 12w01a)

New packets

Unknown (0xFA)

Packet ID	Field Name	Field Type	Example	Notes
0xFA	Unknown	string
	Length of array	short		Length of the following array
	Array	byte[]
Total Size:	5 bytes + string + array

Changed packets

Login Request (0x01)

New string field added

Client to Server

Packet ID	Field Name	Field Type	Example	Notes
0x01	Protocol Version	int	20	1.0.0's protocol version is 22
	Username	string	TkTech	The name of the user attempting to login, max length of 16
	Not used	long	0
	Unknown	string
	Not used	int	0
	Not used	byte	0
	Not used	byte	0
	Not used	unsigned byte	0
	Not used	unsigned byte	0
Total Size:	25 bytes + length of strings

Server to Client

Packet ID	Field Name	Field Type	Example	Notes
0x01	Entity ID	int	1298	The Players Entity ID
	Not used	string	(empty string)	Not used
	Map Seed	long	971768181197178410	The server's map seed. Must be sent in respawn packets by the client.
	Unknown	string
	Server mode	int	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
	World height	unsigned byte	128	Defaults to 128
	Max players	unsigned byte	8	Used by the client to draw the player list
Total Size:	25 bytes + length of strings

Respawn (0x09)

New string field added

Packet ID	Field Name	Field Type	Example	Notes
0x09	Dimension	byte	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	128	Defaults to 128
	Map Seed	long	-3815848935435401459
	Unknown	string
Total Size:	16 bytes + length of string

Other changes

None currently.

Protocol History

2012-01-05

• 12w01a
• Protocol version is now 23

2011-12-15

• 11w50a

2011-12-08

• 11w49a

2011-12-01

• 11w48a

2011-11-24

• 11w47a