Pre-release protocol

This page documents the changes from the last stable Minecraft release (currently 1.4.5, protocol 49) to the current pre-release (or weekly release). Note that this page contains bleeding-edge information that may not be completely or correctly documented.

New Packets

-None-

Changed Packets

Held Item Change (0x10)

Two-Way

Sent when the player changes the slot selection, Server sends it when you travel to a different dimension.

Packet ID	Field Name	Field Type	Example	Notes
0x10	Slot ID	short	1	The slot which the player has selected (0-8)
Total Size:	3 bytes

Changed Data Types

Spawn Object/Vehicle (0x17)

Server to Client

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
	Yaw	byte	592	The yaw in steps of 2p/256
	Pitch	byte	592	The pitch in steps of 2p/256
	Object Data			Object Data
	Total Size:	22 or 28 bytes

Map Chunk Bulk (0x38)

Server to Client

Packet ID	Field Name	Field Type	Example	Notes
0x38	Chunk Count	short		The number of chunks in this packet
	Chunk data length	int		the size of the data field
	Unknown use	boolean		Has only been observed as true when sniffing a vanilla connection.
	Data	byte array		Compressed chunk data
	meta information	chunk bulk meta information		Chunk count times the Meta information structure (See notes for details)
Total Size:	7 + (Chunk data size) + 12 * (Chunk Count) bytes

Removed Packets

0x15 "Spawn Dropped Item" has been removed, and its purpose is now handled by 0x17 "Spawn Object/Vehicle". The entity type ID is 0x02. You can set the item type by sending an 0x18 "Entity Metadata" packet with a slot at index 10. Vanilla packet dump

Protocol History

1.4.6 Pre-release

Protocol version is now 51. Spawn dropped item (0x15) removed, merged into spawn object (0x17). Map chunk bulk (0x38) adds a boolean field with unknown purpose.

12w49a

Protocol version is now 50. Packet 0x10 is sent both ways. Packet 0x17 has two new bytes, currently unknown.