Pre-release protocol

This page documents the changes from the last stable Minecraft release (currently 1.1) to the current pre-release

New packets

Entity Head Look (0x23)

Changes the direction an entity's head is facing.

Packet ID	Field Name	Field Type	Example	Notes
0x23	Entity ID	int
	Head Yaw	byte		Head yaw in steps of 2π/256
Total Size:	6 bytes

Update Tile Entity (0x84)

Essentially a block update on a tile entity.

Packet ID	Field Name	Field Type	Example	Notes
0x84	X	int
	Y	short
	Z	int
	Action	byte		The type of update to perform
	Custom 1	int		Varies
	Custom 2	int		Varies
	Custom 3	int		Varies
Total Size:	24 bytes

Actions

• 1: Set mob displayed inside a mob spawner. Custom 1 contains the mob type

Changed packets

Login Request (0x01)

World height was changed to an integer.

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.
	Level Type	string	DEFAULT	DEFAULT or SUPERFLAT; level-type in server.properties
	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	int	256	Defaults to 256
	Max players	unsigned byte	8	Used by the client to draw the player list
Total Size:	28 bytes + length of strings

TODO: Figure out other packets

Handshake (0x02)

Client to Server

The hostname and port were added to this packet, most likely to allow virtual hosting .(sample implementation)

Packet ID	Field Name	Field Type	Example	Notes
0x02	UsernameAndHost	string	TkTech;localhost:25565	The username of the player attempting to connect, and the host he is connecting to, seperated by a semicolon.
Total Size:	3 bytes + length of strings

Mob Spawn (0x18)

New byte field: head yaw

This needs confirmation!

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 2π/256
	Pitch	byte	0	The pitch in steps of 2π/256
	Head Yaw	byte		Head yaw in steps of 2π/256
	Metadata	Metadata	127	Varies by mob, see Entities
Total Size:	21 bytes + Metadata (at least 1)

Map Chunk (0x33)

This is currently a best guess

Packet ID	Field Name	Field Type	Example	Notes
0x33	X	int		Chunk X Coordinate (x16 to get true X) Confirmed!
	Z	int		Chunk Z Coordinate (x16 to get true Z) Confirmed!
	Unknown Bool	boolean		Seems to be True when Unknown Short #1 is 2^n - 1
	Unknown Short #1	short		Possibly the dimensions in all directions. Or Y offset?
	Unknown Short #2	short		I've only seen 0
	Compressed size	int		Size of compressed region data. Confirmed!
	Unknown Int	int		Doesn't seem to be used by the client. Always 0. I expect this is Mod API stuff.
	Compressed data	unsigned byte array	…	The region data is compressed using ZLib Deflate function. Confirmed!
Total Size:	22 bytes + Compressed chunk size

Other changes

Protocol version is now 27.

Protocol History

2012-02-15

• 12w07a
• Protocol version is now 27
• Updated packets: 0x01, 0x09, 0x33

2012-02-09

• 12w06a
• Protocol version is now 25
• New packet: 0x84

2012-01-26

• 12w04a
• Protocol version has not been changed
• Handshake Packet by client (0x02) now contains the server host and port
• Window Open Packet (0x64): WindowTitle is now longer than accepted by older clients. Contains a keyword such as "container.furnace"

2012-01-19

• 12w03a
• Protocol version is now 24
• New packet: 0x23
• MobSpawn: new field, 1 byte inserted before metadata.