Pre-release protocol

This page documents the changes from the last stable Minecraft release (currently 1.7.4, protocol 4) to the current pre-release. Note that this page contains bleeding-edge information that may not be completely or correctly documented. He who wishes to commandeer the merging of this into Protocol when an update is made must be sure to respect any changes that may have occured to the respective packets there.

Protocol History

14w02a

• Added 'Position' to Chat Message Clientbound
• Remove Player Position And Look's 'OnGround' clientbound
• Added 'Flags' to Player Position And Look clientbound
• Changed Open Inventory's 'Inventory Type' type from byte to string
• Added Server Difficulty
• Removed Client Settings' 'Difficulty'

Protocol Version

Version	Protocol
14w02a	5

Play

Clientbound

Chat Message

Identifying the difference between Chat/System Message is important as it helps respect the user's chat visibility options. While position 2 accepts json formatting it will not display, old style formatting works

Packet ID	Field Name	Field Type	Notes
0x02	JSON Data	String	https://gist.github.com/thinkofdeath/e882ce057ed83bac0a1c , Limited to 32767 bytes
	Position	Byte	0 - Chat (chat box) ,1 - System Message (chat box), 2 - Above action bar

Malformed JSON will disconnect the client

Player Position And Look

Updates the players position on the server. If the distance between the last known position of the player on the server and the new position set by this packet is greater than 100 units will result in the client being kicked for "You moved too quickly :( (Hacking?)" Also if the fixed-point number of X or Z is set greater than 3.2E7D the client will be kicked for "Illegal position"

Yaw is measured in degrees, and does not follow classical trigonometry rules. The unit circle of yaw on the XZ-plane starts at (0, 1) and turns counterclockwise, with 90 at (-1, 0), 180 at (0,-1) and 270 at (1, 0). Additionally, yaw is not clamped to between 0 and 360 degrees; any number is valid, including negative numbers and numbers greater than 360.

Pitch is measured in degrees, where 0 is looking straight ahead, -90 is looking straight up, and 90 is looking straight down.

The yaw of player (in degrees), standing at point (x0,z0) and looking towards point (x,z) one can be calculated with:

 l = x-x0
 w = z-z0
 c = sqrt( l*l + w+w )
 alpha1 = -arcsin(l/c)/PI*180
 alpha2 =  arccos(w/c)/PI*180
 if alpha2 > 90 then
   yaw = 180 - alpha1
 else
   yaw = alpha1

You can get a unit vector from a given yaw/pitch via:

 x = -cos(pitch) * sin(yaw)
 y = -sin(pitch)
 z =  cos(pitch) * cos(yaw)

About the flags field:

 <Dinnerbone> It's a bitfield, X/Y/Z/Y_ROT/X_ROT. If X is set, the x value is relative and not absolute.

Packet ID	Field Name	Field Type	Notes
0x08	X	Double	Absolute/Relative position
	Y	Double	Absolute/Relative position
	Z	Double	Absolute/Relative position
	Yaw	Float	Absolute/Relative rotation on the X Axis, in degrees
	Pitch	Float	Absolute/Relative rotation on the Y Axis, in degrees
	Flags	Byte	X 0x01 Y 0x02 Z 0x04 Y_ROT 0x08 X_ROT 0x10

Open Window

This is sent to the client when it should open an inventory, such as a chest, workbench, or furnace. This message is not sent anywhere for clients opening their own inventory.

Packet ID	Field Name	Field Type	Notes
0x2D	Window id	Unsigned Byte	A unique id number for the window to be displayed. Notchian server implementation is a counter, starting at 1.
	Inventory Type	String	The window type to use for display. Check below
	Window title	String	The title of the window.
	Number of Slots	Unsigned Byte	Number of slots in the window (excluding the number of slots in the player inventory).
	Use provided window title	Bool	If false, the client will look up a string like "window.minecart". If true, the client uses what the server provides.
	Entity ID	Int	EntityHorse's entityId. Only sent when window type is equal to "EntityHorse".

See inventory windows for further information.

Server Difficulty

Changes the difficulty setting in the client's option menu

Packet ID	Field Name	Field Type	Notes
0x41	Difficulty	Unsigned Byte	0:PEACEFUL, 1:EASY, 2:NORMAL, 3: HARD

Serverbound

Client Settings

Sent when the player connects, or when settings are changed.

Packet ID	Field Name	Field Type	Notes
0x15	Locale	String	en_GB
	View distance	Byte	0-3 for 'far', 'normal', 'short', 'tiny'.
	Chat flags	Byte	Chat settings. See notes below.
	Chat colours	Bool	"Colours" multiplayer setting
	Show Cape	Bool	Client-side "show cape" option

Chat flags has several values packed into one byte.

Chat Enabled: Bits 0-1. 00: Enabled. 01: Commands only. 10: Hidden.