Protocol

This page presents a dissection of the current stable Minecraft Beta protocol. The current pre-release protocol is documented elsewhere.

Credit goes to the Great Old Ones, and the citizens of #mcdevs who helped by providing packet dumps and insight. If you're having trouble, check out the FAQ.

Note: While you may use the contents of this page without restriction to create servers, clients, bots, etc… you still need to provide the attribution above if you copy any of the contents of this page for publication elsewhere.

The protocol for Pocket Minecraft is substantially different, and is documented at Pocket Minecraft Protocol.

Data Types

All types in Java (and as such Minecraft) are big-endian, that is, the most significant byte comes first. The majority of everyday computers are little endian, and using most programming languages will require converting big endian values to little endian.

These data formats are identical to those provided by the Java classes DataInputStream and DataOutputStream.

	Size	Range	Notes
byte	1	-128 to 127	Signed, two's complement
short	2	-32768 to 32767	Signed, two's complement
int	4	-2147483648 to 2147483647	Signed, two's complement
long	8	-9223372036854775808 to 9223372036854775807	Signed, two's complement
float	4	See this	Single-precision 32-bit IEEE 754 floating point
double	8	See this	Double-precision 64-bit IEEE 754 floating point
string16	≥ 2 ≤ 240	N/A	UCS-2 string, big-endian. Prefixed by a short containing the length of the string in characters. UCS-2 consists of 16-bit words, each of which represent a Unicode code point between U+0000 and U+FFFF inclusive.
bool	1	0 or 1	Value can be either True (0x01) or False (0x00)
metadata	Varies	See this

Terminology

This is a fairly lengthy page, and to make it more readable certain terminology must be understood. Terms used on this page and their definition are provided below.

	Definition
Player	When used in in the singular, Player always refers to the client connected to the server
Entity	Entity refers to any item, player, mob, minecart or boat in the world. This definition is subject to change as Notch extends the protocol
EID	An EID - or Entity ID - is a unique 4-byte integer used to identify a specific entity
XYZ	In this document, the axis names are the same as those used by Notch. Y points upwards, X points South, and Z points West.

Units of Measurement

There are several different units of measurement used in the protocol depending on what is being described. For example, it wouldn't make much sense to send the position of a block (which is a constant multiple of 32) in a floating point double.

A block represents 1 meter x 1 meter x 1 meter. There are 32 pixels per meter, and chunks are 16m x 128m x 16m.

	Data Types	Units	Represents
Absolute	double	meters	Represents an object's location in the world.
Absolute Integer	int	pixels	Represents an object's location in the world. Functions the same as Absolute Double, but requires fewer bytes and is less precise. In C/C++/Java: absolute_int = (int)(absolute_double * 32.0);
Block	byte, short, int	meters	Represents a block's location in the world.
Chunk	short, int	chunks	Represents the position of a chunk.

Packets

All packets begin with a single "Packet ID" byte. Listed packet size includes this byte. Packets are either "server to client", "client to server", or both. If not specified, assume that the packet can be sent both ways. There is no "length" field; for variable length packets, you must parse to the end to determine the length.

Keep Alive (0x00)

The server will frequently send out a keep-alive, each containing a random ID. The client must respond with the same packet. The Beta server will disconnect a client if it doesn't receive at least one packet before 1200 in-game ticks, and the Beta client will time out the connection under the same conditions. The client may send packets with Keep-alive ID=0.

Packet ID	Field Name	Field Type	Example	Notes
0x00	Keep-alive ID	int	957759560	Server-generated random id
Total Size:	5 bytes

Login Request (0x01)

Client to Server

Sent by the client after the handshake to finish logging in. If the version is outdated or any field is invalid, the server will disconnect the client with a kick. If the client is started in offline mode, the player's username will default to Player, making LAN play with more than one player impossible (without authenticating) as the server will prevent multiple users with the same name.

Packet ID	Field Name	Field Type	Example	Notes
0x01	Protocol Version	int	20	1.8.1's protocol version is 17
	Username	string16	TkTech	The name of the user attempting to login, max length of 16
	Not used	long	0
	Not used	int	0
	Not used	byte	0
	Not used	byte	0
	Not used	unsigned byte	0
	Not used	unsigned byte	0
Total Size:	23 bytes + length of strings

Server to Client

Sent by the server if it accepts the clients login request. If it didn't, it'll send a kick instead.

Max players is used by the client to draw the player list. Setting this value lower than the actual max players, or indeed the number of players online, will only affect the size and number of users displayed. Values above 127 will cause the player list not to be drawn. Values above 60 will cause usernames to overlap and not fit in their bounding boxes.

Packet ID	Field Name	Field Type	Example	Notes
0x01	Entity ID	int	1298	The Players Entity ID
	Not used	string16	(empty string)	Not used
	Map Seed	long	971768181197178410	The server's map seed. Must be sent in respawn packets by the client.
	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:	23 bytes + length of strings

Handshake (0x02)

Client to Server

This is the first packet sent when the client connects and is used for Authentication.

Packet ID	Field Name	Field Type	Example	Notes
0x02	Username	string16	TkTech	The username of the player attempting to connect, max length of 16
Total Size:	3 bytes + length of strings

Server to Client

This is the first packet sent when the client connects and is used for Authentication.

Packet ID	Field Name	Field Type	Example	Notes
0x02	Connection Hash	string16	2e66f1dc032ab5f0	A unique, per-connection hash, or '-', or '+'
Total Size:	3 bytes + length of strings

Possible values for Connection Hash:

Value	Meaning: What the client will do
The string '-'	No Auth: The client continues without doing name authentication.
The string '+'	Password Auth: There is currently no way to send a password in at least version 1.8.1. It should be treated similarly to '-'.
Anything else, will be a randomly generated long as a string of hex digits	Name Auth with minecraft.net: This hash, as of the latest version of the Beta server, is a randomly generated long in hexadecimal form, and has nothing to do with the client or the server it is connected to. The client proceeds to use this hash to log in via minecraft.net.

Chat Message (0x03)

A message from the client to the server, or the server to the client. The actual handling of chat messages is variable and depends on the server and client; there are no de facto standards yet.

The Alpha server will check the message to see if it begins with a '/'. If it doesn't, the username of the sender is prepended and sent to all other clients (including the original sender). If it does, the server assumes it to be a command and attempts to process it. A message longer than 100 characters will cause the server to kick the client. This limits the chat message packet length to 103 bytes. Note that this limit does not apply to incoming chat messages as the server may have prepended other information, not limited to, but usually including, a username.

A message longer than 119 characters will cause the Beta (≥1.5) server and client to crash to print the message "Received string length longer than maximum allowed (X > 119)", with no side effects.

For more information, see Chat.

Packet ID	Field Name	Field Type	Example	Notes
0x03	Message	string16	<Bob> Hello World!	User input must be sanitized server-side
Total Size:	3 bytes + length of strings

Time Update (0x04)

Server to Client only

Time is based on ticks, where 20 ticks happen every second. There are 24000 ticks in a day, making Minecraft days exactly 20 minutes long.

The time of day is based on the timestamp modulo 24000. 0 is sunrise, 6000 is noon, 12000 is sunset, and 18000 is midnight.

The default SMP server increments the time by 20 every second.

Packet ID	Field Name	Field Type	Example	Notes
0x04	Time	long		The world (or region) time, in ticks
Total Size:	9 bytes

Entity Equipment (0x05)

After each "Named Entity Spawn", there will be five of these packets for the equipped item and armor. If there are changes in visible equipment, another one of these is sent.

Packet ID	Field Name	Field Type	Example	Notes
0x05	Entity ID	int	0x00010643	Named Entity ID
	Slot	short	4	Equipment slot: 0=held, 1-4=armor slot
	Item ID	short	-1	Equipped item (-1 for empty slot)
	Damage	short
Total Size:	11 bytes

Spawn Position (0x06)

Server to Client only

Sent by the server after login to specify the coordinates of the spawn point (the point at which players spawn at, and which the compass points to). It can be sent at any time to update the point compasses point at.

Packet ID	Field Name	Field Type	Example	Notes
0x06	X	int	117	Spawn X in block coordinates
	Y	int	70	Spawn Y in block coordinates
	Z	int	-46	Spawn Z in block coordinates
Total Size:	13 bytes

Use Entity (0x07)

Client to Server only

This packet is new to version 4 of the protocol, and is believed to be Use Entity. This packet is sent from the client to the server when the client attacks or right-clicks another entity.

A Notchian server only accepts this packet if the entity being attacked/used is visible without obstruction and within a 4-unit radius of the player's position.

(This packet data values are not fully verified)

Packet ID	Field Name	Field Type	Example	Notes
0x07	User	int	1298	The entity of the player (ignored by the server)
	Target	int	1805	The entity the player is interacting with
	Left-click?	bool	true	Seems to be true when the player is pointing at an entity and left-clicking and false when right-clicking.
Total Size:	10 bytes

Update Health (0x08)

Server to Client only

Sent by the server to update/set the health of the player it is sent to. Added in protocol version 5.

Food saturation acts as a food "overcharge". Food values will not decrease while the saturation is over zero. Players logging in automatically get a saturation of 5.0. Eating food increases the saturation as well as the food bar.

Packet ID	Field Name	Field Type	Example	Notes
0x08	Health	short	20	0 or less = dead, 20 = full HP
	Food	short	20	0 - 20
	Food Saturation	float	5.0	Seems to vary from 0.0 to 5.0 in integer increments
Total Size:	9 bytes

Respawn (0x09)

Sent by the client when the player presses the "Respawn" button after dying. The server then teleports the user to the spawn point, and sends a respawn packet in response. The client will not leave the respawn screen until it receives a respawn packet.

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
Total Size:	14 bytes

Player (0x0A)

Client to Server only

This packet is used to indicate whether the player is on ground (walking/swimming), or airborne (jumping/falling).

When dropping from sufficient height, fall damage is applied when this state goes from False to True. The amount of damage applied is based on the point where it last changed from True to False. Note that there are several movement related packets containing this state.

This packet was previously referred to as Flying

Packet ID	Field Name	Field Type	Example	Notes
0x0A	On Ground	bool	1	True if the client is on the ground, False otherwise
Total Size:	2 bytes

Player Position (0x0B)

Client to Server (player-controlled movement).

Updates the players XYZ position on the server. If Stance - Y is less than 0.1 or greater than 1.65, the stance is illegal and the client will be kicked with the message “Illegal Stance”. If the distance between the last known position of the player on the server and the new position set by this packet has a distance greater than 100 units will result in the client being kicked for "You moved too quickly :( (Hacking?)" Also if the absolute number of X or Z is set greater than 3.2E7D the client will be kicked for "Illegal position"

Packet ID	Field Name	Field Type	Example	Notes
0x0B	X	double	102.809	Absolute position
	Y	double	70.00	Absolute position
	Stance	double	71.62	Used to modify the players bounding box when going up stairs, crouching, etc…
	Z	double	68.30	Absolute position
	On Ground	bool	1	Derived from packet 0x0A
Total Size:	34 bytes

Player Look (0x0C)

Client to Server (player-controlled movement).

The unit circle for yaw

Updates the direction the player is looking in.

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 backwards towards (-1, 0), or in other words, it turns clockwise instead of counterclockwise. 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.

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)

Packet ID	Field Name	Field Type	Example	Notes
0x0C	Yaw	float	0.00	Absolute rotation on the X Axis, in degrees
	Pitch	float	0.00	Absolute rotation on the Y Axis, in degrees
	On Ground	bool	1	Derived from packet 0x0A
Total Size:	10 bytes

Player Position & Look (0x0D)

A combination of Player Look and Player position.

Client to Server

Packet ID	Field Name	Field Type	Example	Notes
0x0D	X	double	6.5	Absolute position
	Y	double	65.620000004768372	Absolute position
	Stance	double	67.240000009536743	Used to modify the players bounding box when going up stairs, crouching, etc…
	Z	double	7.5	Absolute position
	Yaw	float	0.0	Absolute rotation on the X Axis
	Pitch	float	0.0	Absolute rotation on the Y Axis
	On Ground	bool	0	Derived from packet 0x0A
Total Size:	42 bytes

Server to Client

Packet ID	Field Name	Field Type	Example	Notes
0x0D	X	double	6.5	Absolute position
	Stance	double	67.240000009536743	Used to modify the players bounding box when going up stairs, crouching, etc…
	Y	double	65.620000004768372	Absolute position
	Z	double	7.5	Absolute position
	Yaw	float	0.0	Absolute rotation on the X Axis
	Pitch	float	0.0	Absolute rotation on the Y Axis
	On Ground	bool	0	Derived from packet 0x0A
Total Size:	42 bytes

Note that this packet differs from client Player & Position Look packet - the Stance and Y are sent in a different order.

Stance and Y seems to be the opposite as in the table (from Client to Server = X, Y, Stance, Z, froom Server to client = X, Stance, Y, Z) please confirm ! [BackBone`:] The opposite stance<->y confirmed, however the given structs had the server and client struct reversed, which I fixed.

When you connect to the official server, it will push a 0x0D packet. If you do not immediately respond with a 0x0D (or maybe 0x0A-0x0C) packet with similar and valid information, it will have unexpected results, such as map chunks not loading and future 0x0A-0x0D packets being ignored.

Player Digging (0x0E)

Sent when the player mines a block. A Notchian server only accepts digging packets with coordinates within a 6-unit radius of the player's position.

Packet ID	Field Name	Field Type	Example	Notes
0x0E	Status	byte	1	The action the player is taking against the block (see below)
	X	int	32	Block position
	Y	byte	64	Block position
	Z	int	32	Block position
	Face	byte	3	The face being hit (see below)
Total Size:	12 bytes

Status can (currently) be one of four values:

Meaning	Value
Started digging	0
Finished digging	2
Drop item	4
Shoot arrow	5

Notchian clients send a 0 (started digging) when they start digging and a 2 (finished digging) once they think they are finished. If digging is aborted, no notice is sent to the server; the client simply does not send a 2 (finished digging).

Status code 4 (drop item) is a special case. In-game, when you use the Drop Item command (keypress 'q'), a dig packet with a status of 4, and all other values set to 0, is sent from client to server.

The face can be one of six values, representing the face being hit:

Value	0	1	2	3	4	5
Offset	-Y	+Y	-Z	+Z	-X	+X

In 1.7.3, when a player opens a door with left click the server receives Packet 0xE+start digging and opens the door.

Player Block Placement (0x0F)

Sent when the player places a block or (probably) an item. The coordinates sent in this packet are actually the block being built against, which combined with the direction offset tell you where the block should be placed. This is required to correctly position furnaces, torches, etc…

In 1.7.3, when a player opens a door with right click, the server receives Packet 0xF (block placement, but opens door).

Packet ID	Field Name	Field Type	Example	Notes
0x0F	X	int	32	Block position
	Y	byte	64	Block position
	Z	int	32	Block position
	Direction	byte	3	The offset to use for block/item placement (see below)
	Held item	slot
Total Size:	11 bytes + slot data

If the Block/ItemID field is greater than or equal to 0, then the last 2 fields (amount and damage) are read. Otherwise, they are not read. When 'placing' (Or more accurately, using) your empty hand, the client sends -1 as the Block/ItemID

The direction can be one of six values, representing the face the block/item is being placed against:

Value	0	1	2	3	4	5
Offset	-Y	+Y	-Z	+Z	-X	+X

In normal operation (ie placing a block), this packet is sent once, with the values set normally.

This packet has a special case where X, Y, Z, and Direction are all -1. This special packet indicates that the currently held item for the player should have its state updated such as eating food, shooting bows, using buckets, etc.

In a Notchian Beta client, the block or item ID corresponds to whatever the client is currently holding, and the client sends one of these packets any time a right-click is issued on a surface, so no assumptions can be made about the safety of the ID. However, with the implementation of server-side inventory, a Notchian server seems to ignore the item ID, instead operating on server-side inventory information and holding selection.

Special note on using buckets: When using buckets, the Notchian client might send two packets: first a normal and then a special case. The first normal packet is sent when you're looking at a block (e.g. the water you want to scoop up). This normal packet does not appear to do anything with a Notchian server. The second, special case packet appears to perform the action - based on current position/orientation and with a distance check - it appears that buckets can only be used within a radius of 6 units.

Holding Change (0x10)

Sent when the player changes the slot selection

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

Use Bed (0x11)

Server to Client
Associated with players using beds.

Packet ID	Field Name	Field Type	Example	Notes
0x11	Entity ID	int	89	Player ID
	???In Bed???	byte	0	0 Appears when players use bed
	X coordinate	int	-247	Bed (headboard?) X as block coordinate
	Y coordinate	byte	78	Bed (headboard?) Y as block coordinate
	Z coordinate	int	128	Bed (headboard?) Z as block coordinate
Total Size:	15 bytes

• NOTE: This Packet seems to be sent when 2 or more players are on a server, and at least one player uses a Bed.

Animation (0x12)

Sent whenever an entity should change animation.

Packet ID	Field Name	Field Type	Example	Notes
0x12	EID	int	55534	Player ID
	Animation	byte	1	Animation ID
Total Size:	6 bytes

Animation can be one of the following values:

ID	Animation
0	No animation
1	Swing arm
2	Damage animation
3	Leave bed
5	Eat food
102	(unknown)
104	Crouch
105	Uncrouch

Only 1 (swing arm) and 3 (leave bed) is sent by notchian clients. Crouching is sent via 0x13. Damage is server-side, and so is not sent by notchian clients. See also 0x26.

Entity Action (0x13)

Client to Server only

Sent at least when crouching, leaving a bed, or sprinting. To send action animation to client use 0x28.

Packet ID	Field Name	Field Type	Example	Notes
0x13	EID	int	55534	Player ID
	Action ID	byte	1	The ID of the action, see below.
Total Size:	6 bytes

Action ID can be one of the following values:

ID	Action
1	Crouch
2	Uncrouch
3	Leave bed
4	Start sprinting
5	Stop sprinting

Named Entity Spawn (0x14)

Server to Client only

The only named entities (at the moment) are players (either real or NPC/Bot). This packet is sent by the server when a player comes into visible range, not when a player joins.

Servers can, however, safely spawn player entities for players not in visible range. The client appears to handle it correctly.

The Notchian client is not okay with receiving player entity packets, including 0x14, that refer to its own username or EID; it will teleport to the absolute origin of the map and fall through the Void any time it receives them.

Packet ID	Field Name	Field Type	Example	Notes
0x14	EID	int	94453	Player ID
	Player Name	string16	Twdtwd	Max length of 16
	X	int	784	Player X as Absolute Integer
	Y	int	2131	Player Y as Absolute Integer
	Z	int	-752	Player Z as Absolute Integer
	Rotation	byte	0	Player rotation as a packed byte
	Pitch	byte	0	Player rotation as a packed byte
	Current Item	short	0	The item the player is currently holding. Note that this should be 0 for "no item", unlike -1 used in other packets. A negative value crashes clients.
Total Size:	23 bytes + length of strings

Pickup Spawn (0x15)

A pickup spawn is sent by the server whenever an item on the ground (say a pickaxe thrown on the ground) comes into range of the player. (note: this means range for item vision, not range for pickup!) It used to be sent by the client when an item is dropped from a tile (chest or furnace) or from inventory, but that is now done with the new packets for server-side inventory (see 0x66).

It is completely acceptable for servers to ignore the EID issued by the client in this packet and instead create a new packet with a server-controlled EID when sending this packet out to clients.

Packet ID	Field Name	Field Type	Example	Notes
0x15	EID	int	157617	Unique entity ID
	Item	short	4	The item ID
	Count	byte	1	The number of items
	Damage/Data	short		New field in beta 1.2 update (see below)
	X	int	133	Item X as Absolute Integer
	Y	int	913	Item Y as Absolute Integer
	Z	int	63552	Item Z as Absolute Integer
	Rotation	byte	252	Item rotation as a packed byte
	Pitch	byte	25	Item pitch as a packed byte
	Roll	byte	12	Item roll as a packed byte
Total Size:	25 bytes

"Damage" field This field is also used to store item metadata. E.g. you mined birch wood(its id is the same as normal wood) so you must set damage to the metadata of birch wood(2). The same case is wool. Id is the same but data is different.For example: you mined blue wool so your damage field should send value 0xB.

Collect Item (0x16)

Server to Client only

Sent by the server when someone picks up an item lying on the ground - its sole purpose appears to be the animation of the item flying towards you. It doesn't destroy the entity in the client memory (0x1D does that), and it doesn't add it to your inventory (0x67 does that). The server only checks for items to be picked up after each Player Position and Player Position & Look packet sent by the client.

Packet ID	Field Name	Field Type	Example	Notes
0x16	Collected EID	int	38
	Collector EID	int	20
Total Size:	9 bytes

Add Object/Vehicle (0x17)

Server to Client only

Sent by the server when an Object/Vehicle is created.

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
	Fireball thrower's entity ID	int	0	It seems that if this is bigger than 0, this is a fireball and the next 3 fields are sent.
	Unknown	short	0	Seems to be used in calculation of the fireball's X
	Unknown	short	0	Seems to be used in calculation of the fireball's Y
	Unknown	short	0	Seems to be used in calculation of the fireball's Z
Total Size:	22 or 28 bytes

Mob Spawn (0x18)

Server to Client only

Sent by the server when a Mob Entity is Spawned

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 X Axis rotation in steps of 2π/256
	Pitch	byte	0	The Y Axis rotation in steps of 2π/256
	Metadata	Metadata	127	Varies by mob, see Entities
Total Size:	20 bytes + Metadata (at least 1)

Entity: Painting (0x19)

This packet shows location, name, and type of painting.

Packet ID	Field Name	Field Type	Example	Notes
0x19	Entity ID	int	0x00000326	Unique entity ID
	Title	String16	Creepers	Name of the painting; max length 13 (length of "SkullAndRoses")
	X	int	50	Center X coordinate
	Y	int	66	Center Y coordinate
	Z	int	-50	Center Z coordinate
	Direction	int	0	Direction the painting faces (0 -z, 1 -x, 2 +z, 3 +x)

Calculating the center of an image: given a (width x height) grid of cells, with (0, 0) being the top left corner, the center is (max(0, width / 2 - 1), height / 2). E.g.

2x1 (1, 0) 4x4 (1, 2)

Experience Orb (0x1A)

Server to Client only

Spawns a one or more experience orbs. Co-ordinates are in absolute units.

Packet ID	Field Name	Field Type	Example	Notes
0x1A	Entity ID	int	105668
	x	int	-1143
	y	int	1952
	z	int	1166
	count	short	7
Total Size:	19 bytes

Stance update (?) (0x1B)

This packet appears used in controlling position, orientation, and crouching. It doesn't seem to be used (see 0x0D).

Packet ID	Field Name	Field Type	Example	Notes
0x1B	???	float
	???	float
	???	float
	???	float
	???	boolean
	???	boolean

Entity Velocity (0x1C)

This packet is new to version 4 of the protocol, and is believed to be Entity Velocity/Motion.

Velocity is believed to be in units of 1/32000 of a block per server tick (200ms); for example, -1343 would move (-1343 / 32000) = -0.04196875 blocks per tick (or -0.20984375 blocks per second).

Each axis' velocity is capped between -0.9 and 0.9 blocks per tick (packet values -28800 to 28800).

(This packet data values are not fully verified)

Packet ID	Field Name	Field Type	Example	Notes
0x1C	Entity ID	int	1805	The entity ID
	Velocity X	short	-1343	Velocity on the X axis
	Velocity Y	short	0	Velocity on the Y axis
	Velocity Z	short	0	Velocity on the Z axis
Total Size:	11 bytes

Destroy Entity (0x1D)

Server to Client only

Sent by the server when an Entity is to be destroyed on the client.

Packet ID	Field Name	Field Type	Example	Notes
0x1D	EID	int	446	Entity ID
Total Size:	5 bytes

Entity (0x1E)

Server to Client only

Most entity-related packets are subclasses of this packet. When sent from the server to the client, it may initialize the entry.

For player entities, either this packet or any move/look packet is sent every game tick. So the meaning of this packet is basically that the entity did not move/look since the last such packet.

Packet ID	Field Name	Field Type	Example	Notes
0x1E	EID	int	446	Entity ID
Total Size:	5 bytes

Entity Relative Move (0x1F)

Server to Client only

This packet is sent by the server when an entity moves less then 4 blocks; if an entity moves more then 4 blocks Entity Teleport should be sent instead.

This packet allows at most four blocks movement in any direction, because byte range is from -128 to 127. Movement is an offset of Absolute Int; to convert relative move to block coordinate offset, divide by 32.

Packet ID	Field Name	Field Type	Example	Notes
0x1F	EID	int	459	Entity ID
	dX	byte	1	X axis Relative movement as an Absolute Integer
	dY	byte	-7	Y axis Relative movement as an Absolute Integer
	dZ	byte	5	Z axis Relative movement as an Absolute Integer
Total Size:	8 bytes

Entity Look (0x20)

Server to Client only

This packet is sent by the server when an entity rotates. Example: "Yaw" field 64 means a 90 degree turn.

Packet ID	Field Name	Field Type	Example	Notes
0x20	EID	int	459	Entity ID
	Yaw	byte	126	The X Axis rotation as a fraction of 360
	Pitch	byte	0	The Y Axis rotation as a fraction of 360
Total Size:	7 bytes

Entity Look and Relative Move (0x21)

Server to Client only

This packet is sent by the server when an entity rotates and moves. Since a byte range is limited from -128 to 127, and movement is offset of Absolute Int, this packet allows at most four blocks movement in any direction. (-128/32 == -4)

Packet ID	Field Name	Field Type	Example	Notes
0x21	EID	int	459	Entity ID
	dX	byte	1	X axis Relative movement as an Absolute Integer
	dY	byte	-7	Y axis Relative movement as an Absolute Integer
	dZ	byte	5	Z axis Relative movement as an Absolute Integer
	Yaw	byte	126	The X Axis rotation as a fraction of 360
	Pitch	byte	0	The Y Axis rotation as a fraction of 360
Total Size:	10 bytes

Entity Teleport (0x22)

Server to Client only

This packet is sent by the server when an entity moves more than 4 blocks.

Packet ID	Field Name	Field Type	Example	Notes
0x22	EID	int	459	Entity ID
	X	int	14162	X axis position as an Absolute Integer
	Y	int	2176	Y axis position as an Absolute Integer
	Z	int	1111	Z axis position as an Absolute Integer
	Yaw	byte	126	The X Axis rotation as a fraction of 360
	Pitch	byte	0	The Y Axis rotation as a fraction of 360
Total Size:	19 bytes

Entity Status (0x26)

Server to Client only

Packet ID	Field Name	Field Type	Example	Notes
0x26	Entity ID	Int	34353
	Entity Status	Byte	0x03	See below
	Total Size:	6 bytes

Entity Status	Meaning
2	Entity hurt
3	Entity dead
6	Wolf taming
7	Wolf tamed
8	Wolf shaking water off itself
9	(of self) Eating accepted by server

Attach Entity (0x27)

This packet is new to version 4 of the protocol, and is believed to be Attach Entity.

This packet is sent when a player has been attached to an entity (e.g. Minecart)

(This packet data values are not fully verified)

Packet ID	Field Name	Field Type	Example	Notes
0x27	Entity ID	int	1298	The player entity ID being attached
	Vehicle ID	int	1805	The vehicle entity ID attached to (-1 for unattaching)
Total Size:	9 bytes

Entity Metadata (0x28)

Packet ID	Field Name	Field Type	Example	Notes
0x28	Entity ID	int	0x00000326	Unique entity ID to update.
	Entity Metadata	Metadata	0x00 0x01 0x7F	Metadata varies by entity. See Entities
Total Size:	5 bytes + Metadata

Entity Effect (0x29)

Packet ID	Field Name	Field Type	Example	Notes
0x29	Entity ID	int	14	Entity ID of a player
	Effect ID	byte	17	See table below
	Amplifier	byte	0
	Duration	short	64
Total Size:	9 bytes

Effects

Only noted effects are currently implemented by the 1.8pre2 client/server

ID	Meaning	Client implementation	Server implementation
1	moveSpeed	Increases player speed and FOV.
2	moveSlowdown	Decreases player speed and FOV.
3	digSpeed	Increases player dig speed
4	digSlowDown	Decreases player dig speed
5	damageBoost
6	heal
7	harm
8	jump
9	confusion	Portal-like effect
10	regeneration	Hearts pulse one-by-one	Caused by golden apple. Health regenerates over 600-tick (30s) period.
11	resistance
12	fireResistance
13	waterBreathing	Bubbles do not decrease underwater
14	invisibility
15	blindness
16	nightVision
17	hunger	Food bar turns green	Caused by poisoning from Rotten Flesh or Raw Chicken
18	weakness
19	poison	Hearts turn yellow	Caused by poisoning from cave (blue) spider

Remove Entity Effect (0x2A)

Packet ID	Field Name	Field Type	Example	Notes
0x2a	Entity ID	int		Entity ID of a player
	Effect ID	byte	17	See table above
Total Size:	6 bytes

Experience (0x2B)

Sent by the server when the client should change experience levels.

The amount of experience needed to reach the next level increases by 10 with each level. At level 0, you need 10 experience to progress to level 1. At level 1, the requirement is 20 to progress, and so forth.

Packet ID	Field Name	Field Type	Example	Notes
0x2B	Experience bar	float	0.5960060358047485	Used for drawing the experience bar - value is between 0 and 1.
	Level	short	8
	Total experience	short	130
Total Size:	9 bytes

Pre-Chunk (0x32)

Server to Client only

This packet is sent by the server to notify the client to initialize (Mode=1) or unload (Mode=0) a chunk. The client is expected to allocate space for a full chunk (currently 16 x 128 x 16 blocks). One or more 0x33 packets will follow, specifying actual data to fill the chunk with.

Whenever you send this packet the client will clear any previous chunk at that spot if one has previously been sent. Clients don't like being in or next to an unloaded chunk, so try not to unload it if players are nearby. If the player appears to be twitching and stuck in place after joining the world, there is probably an unloaded chunk too close to them.

When sending initial terrain to spawn the player, make sure all pre-chunks are sent before all chunks.

Packet ID	Field Name	Field Type	Example	Notes
0x32	X	int	-9	Chunk X Coordinate
	Z	int	12	Chunk Z Coordinate
	Mode	bool	1	If mode is 0 the client will unload the chunk, otherwise the client will initialize the chunk
Total Size:	10 bytes

Map Chunk (0x33)

Server to Client only

The client will overwrite all or part of a chunk using the region of data contained in this packet. The server specifies the region to write using a block position and size in X,Y,Z. Note that this region will always be inside a single chunk. (At least using the vanilla server. Unknown if the client has this limitation.)

When a client doesn't have a chunk loaded, the server will send a 0x32 packet first (with mode=true) to tell the client to initialize the chunk, followed by a 0x33 packet containing all of the chunk data. 0x32 packet is not sent by the server when updating a chunk that the client already has loaded.

Packet ID	Field Name	Field Type	Example	Notes
0x33	X	int	128	Block X Coordinate
	Y	short	0	Block Y Coordinate
	Z	int	-192	Block Z Coordinate
	Size_X	byte	15	Size_X is Actual X Size -1
	Size_Y	byte	127	Size_Y is Actual Y Size -1
	Size_Z	byte	15	Size_Z is Actual Z Size -1
	Compressed size	int	3663	Size of compressed region data
	Compressed data	byte array	…	The region data is compressed using ZLib Deflate function.
Total Size:	18 bytes + Compressed chunk size

X, Y, Z

This is the start position of the region, in world block coordinates.

To find which chunk is affected, in the same coordinates given by packet 0x32:

 ChunkX = X >> 4 
 ChunkY = Y >> 7
 ChunkZ = Z >> 4

And conversely, which local block in the chunk to start at:

 StartX = X & 15
 StartY = Y & 127  (not always 0!)
 StartZ = Z & 15

SizeX, SizeY, SizeZ

This is the size of the region, in blocks. The server will subtract one from the sizes and then cast them to a byte before sending. This is so that chunks as large as 256 are possible (the maximum size of a byte is 255; 256 - 1 = 255).

Compressed data

The data is compressed using the deflate() function in zlib. After uncompressing, the data consists of four sequential sections, in order:

• Block type array (1 byte per block)
• Block metadata array (half byte/nibble per block)
• Block Light array (half byte/nibble per block)
• Sky Light array (half byte/nibble per block)

The data is exactly (Size_X+1) * (Size_Y+1) * (Size_Z+1) * 2.5 bytes long. Nibbles are not rounded either direction, which means that at least one dimension of the chunk must be even.

The arrays are not interlaced.

In other words, there are Size_X number of x planes, each plane made up of Size_Z number of z rows, each row made up of Size_Y blocks indexed by y coordinate in order.

The block type array is indexed with:

 index = y + (z * (Size_Y+1)) + (x * (Size_Y+1) * (Size_Z+1))

The other arrays are similar but you need to divide the index by two after calculating the above. Then each byte contains data for two blocks. The low four bits contain the first (lower Y) nibble and the high four bits contain the second nibble.

If you have a FULL map chunk (Size_X = 15, Size_Y = 127, Size_Z = 15, you can calculate index coordinates:

 x = X + ( index >> 11 )
 y = index & 0x7F
 z = Z + ( (index & 0x780) >> 7 )

Multi Block Change (0x34)

Further investigation shows that this is a multiple-block-change command; if you take the three arrays, and put together elements with the same index, and then decompose the short into coordinates (top 4 bits is X, next 4 bits is Z, bottom 8 bits is Y), you get things like [((8, 7, 4), 11, 0), ((7, 13, 6), 11, 0), ((13, 1, 8), 11, 0), ((7, 6, 6), 11, 0)].

See the Block Change command for description of the general format of a block change.

Packet ID	Field Name	Field Type	Example	Notes
0x34	Chunk X	int	-9	Chunk X Coordinate
	Chunk Z	int	12	Chunk Z Coordinate
	Array size	short	2	The total number of elements per array
	Coordinate array	short array	…	The coordinates of the blocks to change
	Type array	byte array	…	The type for each block change
	Metadata array	byte array	…	The Metadata for each block changed
Total Size:	11 bytes + Arrays

Block Change (0x35)

Block metadata varies by block type - it should be 0x00 for most blocks with a few exceptions, shown in the table below.

Packet ID	Field Name	Field Type	Example	Notes
0x35	X	int	502	Block X Coordinate
	Y	byte	71	Block Y Coordinate
	Z	int	18	Block Z Coordinate
	Block Type	byte	78	The new block type for the block
	Block Metadata	byte	0	The new Metadata for the block
Total Size:	12 bytes

Block Action (0x36)

Server to Client only

This packet is used for a number of things:

• Chests opening and closing
• Pistons pushing and pulling
• Note blocks playing

Packet ID	Field Name	Field Type	Example	Notes
0x35	X	int	502	Block X Coordinate
	Y	short	71	Block Y Coordinate
	Z	int	18	Block Z Coordinate
	Byte 1	byte	3	Varies depending on block - see below
	Byte 2	byte	17	Varies depending on block - see below
Total Size:	13 bytes

Note Block

It shows the note particle being emitted from the block as well as playing the tone.

Byte 1

Instrument type.

Type ID	Type Name
0	Harp
1	Double Bass
2	Snare Drum
3	Clicks/Sticks
4	Bass Drum

Byte 2

The pitch of the note (between 0-24 inclusive where 0 is the lowest and 24 is the highest). More information about how the pitch values correspond to notes in real life are available on the official Minecraft wiki.

Piston

Byte 1

The state the piston changes to - 0 for pushing, 1 for pulling.

Byte 2

Direction.

Direction ID	Direction
0	Down
1	Up
2	South
3	West
4	North
5	East

Chest

Animates the chest's lid opening. Note that the notchian server will send this every 3s even if the state hasn't changed.

Byte 1

Not used - always 1

Byte 2

State of the chest - 0 for closed, 1 for open.

Explosion (0x3C)

This command is not fully understood.

Seems to be sent when an explosion occurs (both creepers and TNT).

Packet ID	Field Name	Field Type	Example	Notes
0x3C	X	double
	Y	double
	Z	double
	Unknown	float	3.0	radius?
	Record count	int		This is the count, not the size. The size is 3 times this value.
	Records	(byte, byte, byte) × count		Each record is 3 bytes, which seem to be XYZ offsets of affected blocks.
Total Size:	33 bytes + 3*(Record count) bytes

Sound/particle effect (0x3D)

Sent when a client is to play a sound or particle effect.

Packet ID	Field Name	Field Type	Example	Notes
0x3D	Effect ID	int	1003	The ID of the effect, see below.
	X	int		The X location of the effect.
	Y	byte		The Y location of the effect.
	Z	int		The Z location of the effect.
	Data	int	0	Extra data for certain effects, see below.
Total Size:	18 bytes

Effects

Effect ID	Name	Data	Notes
1000	CLICK2
1001	CLICK1
1002	BOW_FIRE
1003	DOOR_TOGGLE
1004	EXTINGUISH
1005	RECORD_PLAY	Record ID [1]
1007	CHARGE		Sound of ghast firing.
1008	FIREBALL		Sound of blaze firing
1009	FIREBALL		Same as above
2000	SMOKE	Direction, check below
2001	BLOCK_BREAK	Block ID broken
2002	SPLASH_POTION	Potion ID [2]	Particle animation and sound
2003	PORTAL		Particle animation
2004	BLAZE (?)		Particle animation (fire + smoke)

Smoke directions:

ID	Direction
0	South - East
1	South
2	South - West
3	East
4	(Up or middle ?)
5	West
6	North - East
7	North
8	North - West

New/Invalid State (0x46)

This packet appeared with protocol version 10. Currently, it appears when a bed can't be used as a spawn point and when the rain state changes. it could have additional uses in the future.

The class has an array of strings linked to reason codes 0, 1, 2, and 3 but only the codes for 1 and 2 are null.

Packet ID	Field Name	Field Type	Example	Notes
0x46	Reason	byte	0
	Game mode	byte	0	Used only when reason = 3. 0 is survival, 1 is creative.
Total Size:	3 bytes

Reason codes

Code	Effect	Text
0	Invalid Bed	"tile.bed.notValid"
1	Begin raining	null
2	End raining	null
3	Change game mode	gameMode.changed
4	Enter credits

Thunderbolt (0x47)

Server to Client only

With this packet, the server notifies the client of thunderbolts striking somewhere (near the player?). The coordinates specify where exactly the thunderbolt strikes.

Packet ID	Field Name	Field Type	Example	Notes
0x47	Entity ID	int	4	The entity ID of the thunderbolt
	Unknown	boolean	true	Always true. Might have a meaning in the future...
	X	int	133	Thunderbolt X as Absolute Integer
	Y	int	913	Thunderbolt Y as Absolute Integer
	Z	int	63552	Thunderbolt Z as Absolute Integer
Total Size:	18 bytes

Open window (0x64)

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	Example	Notes
0x64	Window id	byte	123	A unique id number for the window to be displayed. Notchian server implementation is a counter, starting at 1.
	Inventory Type	byte	2	The window type to use for display. Check below
	Window title	string16	Chest	The title of the window.
	Number of Slots	byte	3	Number of slots in the window (excluding the number of slots in the player inventory).
Total Size:	6 bytes + length of string

The window titles sent by the Notchian server are "Chest", "Large chest", "Crafting", "Furnace", and "Trap". Notchian clients force window titles for some windows, like dispensers and furnaces, but other titles are customizable. However, the window title sent by the server is always used for chests. See inventory windows for further information.

Close window (0x65)

This packet is sent by the client when closing a window. This packet is sent from the server to the client when a window is forcibly closed, such as when a chest is destroyed while it's open.

Note, notchian clients send a close window message with window id 0 to close their inventory even though there is never an Open Window message for inventory.

Packet ID	Field Name	Field Type	Example	Notes
0x65	Window id	byte	0	This is the id of the window that was closed. 0 for inventory.
Total Size:	2 bytes

Window click (0x66)

Client to Server only

This command is not fully understood.

This packet is sent by the player when it clicks on a slot in a window.

Packet ID	Field Name	Field Type	Example	Notes
0x66	Window id	byte	0	The id of the window which was clicked. 0 for player inventory.
	Slot	short	36	The clicked slot. See below.
	Right-click	byte	1	1 when right-clicking and otherwise 0.
	Action number	short	12	A unique number for the action, used for transaction handling (See the Transaction packet).
	Shift	bool	0	This is true if the user was holding keyboard shift when they clicked.
	Clicked item	slot
Total Size:	10 bytes (+3 for item ID != -1)

See inventory windows for further information about how slots are indexed.

When right-clicking on a stack of items, half the stack will be picked up and half left in the slot. If the stack is an odd number, the half left in the slot will be smaller of the amounts.

The Action number is actually a counter, starting at 1. This number is used by the server as a transaction ID to send back a Transaction packet.

The Item (short, optional byte,short) is a critical piece of information in this packet. The Item that is sent by the client is what is in the slot before it is clicked. The server compares that with it's notes, and accepts the transaction if items match. Note that the client seems to send valid item IDs (rather than -1) even when Item count == 0.

Set slot (0x67)

Server to Client only

This command is not fully understood.

Sent by the server when an item in a slot (in a window) is added/removed.

Packet ID	Field Name	Field Type	Example	Notes
0x67	Window id	byte	0	The window which is being updated. 0 for player inventory. Note that all known window types include the player inventory. This packet will only be sent for the currently opened window while the player is performing actions, even if it affects the player inventory. After the window is closed, a number of these packets are sent to update the player's inventory window (0).
	Slot	short	36	The slot that should be updated
	Slot data	slot
Total Size:	4 bytes + slot data

Note that if window ID and slot are both -1, it means the item currently attached to the cursor.

See inventory windows for further information about how slots are indexed.

Slots: [3]

Window items (0x68)

Server to Client only

The inventory slots

Sent by the server when an item in a slot (in a window) is added/removed. This includes the main inventory, equipped armour and crafting slots.

Packet ID	Field Name	Field Type	Example	Notes
0x68	Window id	byte	1	The id of window which items are being sent for. 0 for player inventory.
	Count	short	4	The number of slots (see below)
	Slot data	array of slots
Total Size:	4 bytes + size of slot data array

See inventory windows for further information about how slots are indexed.

Update progress bar (0x69)

Server to Client only

Packet ID	Field Name	Field Type	Example	Notes
0x69	Window id	byte	2	The id of the window that the progress bar is in.
	Progress bar	short	1	Which of the progress bars that should be updated. (For furnaces, 0 = progress arrow, 1 = fire icon)
	Value	short	650	The value of the progress bar. The maximum values vary depending on the progress bar. Presumably the values are specified as in-game ticks. Some progress bar values increase, while others decrease. For furnaces, 0 is empty, full progress arrow = about 180, full fire icon = about 250)
Total Size:	6 bytes

Transaction (0x6A)

A packet from the server indicating whether a request from the client was accepted, or whether there was a conflict (due to lag). This packet is also sent from the client to the server in response to a server transaction rejection packet.

Packet ID	Field Name	Field Type	Example	Notes
0x6A	Window id	byte	0	The id of the window that the action occurred in.
	Action number	short	12	Every action that is to be accepted has a unique number. This field corresponds to that number.
	Accepted?	boolean	true	Whether the action was accepted.
Total Size:	5 bytes

Creative inventory action (0x6B)

While the user is in the standard inventory (i.e., not a crafting bench) on a creative-mode server then the server will send this packet:

• If an item is dropped into the quick bar
• If an item is picked up from the quick bar (special case: item id is -1 and quantity/damage are both 0)

Packet ID	Field Name	Field Type	Example	Notes
0x6B	Slot	short	36	Inventory slot
	Clicked item	slot
Total Size:	3 bytes + slot data

Enchant Item (0x6C)

Client to Server only

Packet ID	Field Name	Field Type	Example	Notes
0x6C	Window ID	byte	1	The ID sent by 0x64
	Enchantment	byte	0	The position of the enchantment on the enchantment table window, starting with 0 as the topmost one.
Total Size:	3 bytes

Update Sign (0x82)

Packet ID	Field Name	Field Type	Example	Notes
0x82	X	int	128	Block X Coordinate
	Y	short	0	Block Y Coordinate
	Z	int	-128	Block Z Coordinate
	Text1	string16	First line	First line of text in the sign
	Text2	string16	Second line	Second line of text in the sign
	Text3	string16	Third line	Third line of text in the sign
	Text4	string16	Fourth line	Fourth line of text in the sign
Total Size:	11 bytes + 4 strings

This message is sent from the server to the client whenever a sign is discovered or created. This message is sent from the client to the server when the "Done" button is pushed after placing a sign. This message is NOT sent when a sign is destroyed or unloaded.

Item Data (0x83)

Server to Client only

Sent to specify complex data on an item; currently used only for maps.

Packet ID	Field Name	Field Type	Example	Notes
0x83	Item Type	short	358	Type of item being modified
	Item ID	short	0	The ID (damage value) of the item being modified
	Text length	unsigned byte	35	Length of following byte array
	Text	byte array	{0,0,0,20,20,20,20,20}	ASCII text.
Total Size:	6 bytes + Text length

Maps If the first byte of the text is 0, the next two bytes are X start and Y start and the rest of the bytes are the colors in that column.

If the first byte of the text is 1, the rest of the bytes are in groups of three: (data, x, y). The lower half of the data is the type (always 0 under vanilla) and the upper half is the direction.

Increment Statistic (0xC8)

Packet ID	Field Name	Field Type	Example	Notes
0xC8	Statistic ID	int	1003	The ID of the statistic. See List of statistics.
	Amount	byte	1	The amount to increment the statistic.
	Total Size:	6 bytes

Player List Item (0xC9)

Sent by the notchian server to update the user list (<tab> in the client). The server sends one packet per user per tick, amounting to 20 packets/s for 1 online user, 40 for 2, and so forth.

Packet ID	Field Name	Field Type	Example	Notes
0xC9	Player name	string16	barneygale	Supports chat colouring, limited to 16 characters.
	Online	bool	true	If false, the client will remove the user from the list.
	Ping	short	193	Ping, presumably in ms.
Total Size:	6 bytes + length of string

Server List Ping (0xFE)

To load server info in the multiplayer menu, the notchian client connects to each known server and sends an 0xFE.

In return, the server sends a kick (0xFF), with its string containing data (server description, number of users, number of slots), delimited by a §.

Note that as this is the last packet you'll see, you can get away with just chopping off the first three bytes (the ident and the string length) and decoding the remainder as a UCS-2 string.

If the number of available slots sent is equal to or less than 0, the client should display it as "???".

Example server pinger:

https://gist.github.com/1209061 (Python)

https://gist.github.com/1235274 (PHP)

Packet ID
0xFE

Disconnect/Kick (0xFF)

Sent by the server before it disconnects a client, or by the client before it disconnects from the server. The receiver of this packet assumes that the sender has already closed the connection by the time the packet arrives.

Packet ID	Field Name	Field Type	Example	Notes
0xFF	Reason	string16	The server is full!	Displayed to the client when the connection terminates
Total Size:	3 bytes + length of strings

Protocol History

Provided below is a changelog of the server protocol starting on 2010-08-20. The wiki history feature may also be used to investigate changes.

2011-11-13

• 1.0rc2
• Protocol version is not changed
• Client gives invalid server key when authentication hash is 8 bytes and the first byte is > 0x80
• Bow has extra metadata as slot item.

2011-11-11

• Beta 1.9 pre6.
• Protocol version is now 22
• NewState: Reason 4 = Enter scrolling text mode after slaying the dragon.
• New entity: EnderCrystal (Spawned using the Add Object/Vehicle (0x17) packet with type 51)

2011-10-27

• Beta 1.9 pre5.
• Protocol version is now 21
• Packet 0x6B (Create Inventory) changed: uses Slot datatype.

2011-10-13

• Beta 1.9 pre4.
• Protocol version is now 20
• Packet 0x2B (Experience) changed: now (float, short, short)
• New packet 0x6C (Enchant item) added: (byte, byte)
• Flint and steel no longer enchantable (see 1.9pre3 changes). Might be others, too.
• Notchian server now features an RCON server (server class: o.java)
• Notchian server now features "G4S" server [4]

2011-9-29

• Beta 1.9 pre2.
• Protocol version is now 19
• Four packets changed:
  • 0x0F player block placement
  • 0x66 window click
  • 0x67 set slot
  • 0x68 window items
• The change affects the "slot" datatype. This type consists of at least a short (item_id). If this id isn't -1, a byte (count) and a short (uses) follow.
• From 1.9pre2 onward, additional data is sent but only for certain item_ids. This means the protocol is no longer context free. The additional data is at least a short. If this short isn't -1, a byte[] array follows, containing gzipped NBT data
• The format of the NBT is as follows

 COMPOUND
   LIST: 'ench'
     SHORT: 'id'
     SHORT: 'lvl'
   END
 END

• So far only this format, with 'id' and 'lvl' set to 2 and 1 respectively, has been seen.

2011-9-22

• Beta 1.9 pre1.
• Protocol version is now 18

2011-9-14

• Beta 1.8 release.
• Protocol version is now 17

2011-9-13

• Beta 1.8 pre2-release.
• Protocol version is now 16
• Packet 0x01 (Login) changed (added byte, world height now unsigned)
• Packet 0x09 (Respawn) changed (added byte)
• Packet 0x64 (Open Window) changed (Window title changed from string8 to string16)
• New packet 0x1a (Experience Orb) added
• Assumedly 0x17 (Add Object/Vehicle) is no longer used for exp orbs.

2011-9-10

• Beta 1.8 pre-release.
• Protocol version is now 15
• Packet 0x00 (Keep Alive) changed (added keep-alive id)
• Packet 0x01 (Login) changed (added server mode, height limit, and an unknown field)
• Packet 0x08 (Health) changed (added food bar and food saturation)
• Packet 0x09 (Respawn) changed (added map seed, server mode, height limit)
• Packet 0x13 (Entity Action) has new values for starting/stopping sprinting.
• Packet 0x46 (New/invalid state) changed (added game mode reason, and a game mode byte)
• New packet 0x29 (Entity Effect) added
• New packet 0x2a (Remove Entity Effect) added
• New packet 0x2b (Experience update) added
• New packet 0x6b (Creative item get) added
• New packet 0xc9 (Player list item) added
• New packet 0xfe (Server list ping) added
• New values for 0x13 (Entity Action): start sprinting, stop sprinting
• New value for 0x17 (Add Object/Vehicle): experience orb

2011-6-30

• Beta 1.7 released.
• Protocol version number is now 14
• No new packets
• Packet 0x36 (Block Action) is now used for pistons too.

2011-5-26

• Beta 1.6 released.
• Protocol increase by 2: 13
• Packet 0x09 (Respawn) changed (added world byte)
• Packet 0x17 (Add Object) changed.
• Packet 0x3d (Sound effect) added
• Packet 0x83 (Map Data) added

2011-4-19

• Beta 1.5 released.
• Some packet info at https://gist.github.com/929803
• Packet 0x01 (Login Request) changed (removed second string)
• Packet 0x66 (Window Click) changed (added bool for shift)
• Added two new packets: 0x47 (Thunderbolt) and 0xC8 (Increment Statistic) (classes eq and nj, respectively)
• Protocol version number is now 11
• All of the strings are now UCS-2, except for Open window (0x64), which is still UTF-8

2011-3-31

• Beta 1.4 released.
• New packet 0x46.
• Protocol version number is now 10
• TODO: The protocol itself does not seem to have changed much, but what about possible data values and stuff like that?

2011-2-22

• Beta 1.3 released.
• New packets 0x11, 0x1B: Some information at https://gist.github.com/841590
• Protocol number is now 9 (updated)

2011-1-13

• Beta 1.2 released.
• More packet changes (pastebin): 0x05, 0x0F, 0x13, 0x15, 0x18, 0x19, 0x28, 0x36, 0x66, 0x67.

2010-12-20

• Notch released Beta on time! Amazing! Refactored the page to be slightly smaller and easier to navigate.
• A whole host of packet changes. 0x05, 0x08, 0x10, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, and 0x82. Packets 0x11 and 0x3b removed.

2010-12-01

• Protocol version changed to 6
• Packet 0x12 (Animation) got a lot more new values
• Packet 0x26 changed, now indicates entity damage, death and explosion (for creepers, TNT not tested)
• Packet 0x3B now being sent from client
• Packet 0x3C added
• (need info on other changes)

2010-11-24

• Protocol version changed to 5
• Packet 0x07 (Use Entity) got a new field (byte)
• Packet 0x08 (Update Health) added
• Packet 0x09 (Respawn) added
• Packet 0x12 (Animation) started getting non-boolean values for the Animation field
• Packet 0x26 (Entity Death) added

2010-11-10

• Protocol version changed to 4
• Packet 0x01 (login request) changed
• Packet 0x07 (Use Entity?) added
• Packet 0x1C (Entity Velocity?) added
• Packet 0x27 (Attach Entity?) added

2010-10-31

• Protocol version changed to 3
• Packet 0x01 (login request) changed

2010-09-10

• Protocol version changed to 2
• Packets 0x05, 0x06, 0x3B added
• Server-side inventory (no verification)
• Vanilla adds experimental monsters (only damaged by fire)

2010-08-20

• Protocol version reset from 14 to 1
• Packet 0x04 (time update) added