Protocol

This page presents a dissection of the new Minecraft Beta protocol. 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.

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.

	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
string	…	N/A	UTF-8 string. Prefixed by a short containing the length of the string
bool	1	0 or 1	Value can be either True (0x01) or False (0x00)
Metadata	[Unknown]	See below	See below

Metadata

The Metadata type provides extra information about an entity, such as sheep color. Metadata was introduced in Beta 1.2. Currently, it takes the following form:

 let x = 0 of type byte
 while (x = read byte from stream) does not equal 127:
     select based on value of (x >> 5):
         case 0: read byte from stream
         case 1: read short from stream
         case 2: read int from stream
         case 3: read float from stream
         case 4: read string from stream
         case 5: read short, byte, short from stream
     end select
 end while

The last 5 bits of x (x & 0x1F) are either an index or bitmask. Currently, only "byte" type metadata has been seen from the server.

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 or mob 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 is always the upwards coordinate, while X and Z are parallel to the ground
MOTD	Message Of The Day

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.

	Type	Represents
Absolute	double	Represents an objects exact location in the world, specified in block coordinates.
Absolute Integer	int	Represents an objects approximate location in the world, specified in pixels. This is the Absolute position cast to an integer, thus losing precision.
Block	int or byte	Represents a blocks exact location in the world. Block = Absolute / 32.
Chunk	int or short	Represents the exact position of a chunk. Chunk = Block / 16.

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)

This packet may be sent to keep the connection alive, or may be a relic of UDP testing. No one is really sure. What we do know is that 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.

Packet ID
0x00

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	8	The latest version of the protocol is 8
	Username	string	TkTech	The name of the user attempting to login
	Password	string	Password	Used to login to password-protected servers
	Map Seed	long	0	This value is not required for the client
	Dimension	byte	0	This value is not required for the client
Total Size:	18 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.

Packet ID	Field Name	Field Type	Example	Notes
0x01	Entity ID	int	1298	The Players Entity ID
	Unknown	string	n/a	Not yet used (Possibly the server name?)
	Unknown	string	n/a	Not yet used (Possibly the MOTD? )
	Map Seed	long	971768181197178410	Used for map generation (Possibly biome determination?)
	Dimension	byte	0	Used for specifying the players dimension -1 for hell, 0 otherwise
Total Size:	18 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	string	TkTech	The username of the player attempting to connect
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. If the hash is '-', then the client continues without doing name authentication. If the hash is a '+', the client sends the server password in the login request. (Note that 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 he is connected to)

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

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.

For more information, see Chat.

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

Time Update (0x04)

Server to Client only

The default SMP server increments the time by 20 every second. The current time ranges from 0 to 24000.

Packet ID	Field Name	Field Type	Example	Notes
0x04	Time	long		The world (or region) time in minutes
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)
	???	short		Damage?
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)

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

(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.

Packet ID	Field Name	Field Type	Example	Notes
0x08	Health	short	20	0 = dead, 20 = full HP
Total Size:	3 bytes

Respawn (0x09)

Sent by the client when the player presses the "Respawn" button after dying. The server then drops the player's inventory, 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
0x09
Total Size: 1 bytes

Player (0x0A)

Client to Server only

This packet is used to identify the state of the client, with the idea being to send one each game-tick to detect speed hackers. Notch will be optimizing/removing this in the future. 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”.

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.

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
	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

Server to Client

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

This packet differs from client Player Position & Look packet, the Stance and Y are sent in a different order, however because of the different order this is sent the client will actually use the X,Y,Stance,Z client layout.

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 repeatedly as the player mines a block.

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
Digging	1
Stopped digging	2
Block broken	3
Drop item	4

When the Status value is 4 (Drop item), the coordinates and Face are 0.

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

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…

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)
	Block or Item ID	short	1	The block or item to be placed
	Amount (opt)	byte	34	The amount of the item in the players hand
	Damage (opt)	short	83	How much damage the item has taken
Total Size:	13 bytes or 16 bytes

If the Block/ItemID field is greater than or equal to 0, then the last 2 bytes (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

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.

The block or item ID corresponds to whatever the client is currently holding, and the Alpha 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.

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

Animation (0x12)

Sent whenever an entity should change animation.

Packet ID	Field Name	Field Type	Example	Notes
0x12	EID	int	55534	Player ID
	Animate	byte	1	Can be 0 (no animation), 1 (swing arm), 2 (damage animation), 104 (crouch), or 105 (uncrouch). Getting 102 somewhat often, too.
Total Size:	6 bytes

Entity Action ??? (0x13)

Sent at least when crouching

Packet ID	Field Name	Field Type	Example	Notes
0x13	EID	int	55534	Player ID
	Action	byte	1	Can be 1 (crouch), or 2 (uncrouch).
Total Size:	6 bytes

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.

Packet ID	Field Name	Field Type	Example	Notes
0x14	EID	int	94453	Player ID
	Player Name	string	Twdtwd
	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
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. 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 ?	short		New field in beta 1.2 update
	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

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).

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 below)
	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
Total Size:	18 bytes

Object Types

Type ID	Type Name
1	Boats
10	Minecart
11	Storage Cart
12	Powered Cart
50	Activated TNT
60	Arrow
61	Thrown Snowball
62	Thrown Egg
70	Falling Sand
71	Falling Gravel
90	Fishing Float

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 Entity Type
	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 as a fraction of 360
	Pitch	byte	0	The Y Axis rotation as a fraction of 360
	Data Stream	Metadata	127	Indexed metadata for Mob (STILL DECODING!). Terminated by 0xf7.
Total Size:	20 bytes + Metadata (at least 1)

Mob Types (Incomplete)

Type ID	Type Name	Metadata
50	Creeper
51	Skeleton
52	Spider
53	Giant Zombie
54	Zombie
55	Slime (random size?)
56	Ghast
57	Zombie Pigman
90	Pig
91	Sheep	Wool color (TODO)
92	Cow
93	Hen

Entity: Painting (0x19)

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

TODO: Verify "Type" field and coordinate type.

Packet ID	Field Name	Field Type	Example	Notes
0x19	Entity ID	int	0x00000326	Unique entity ID
	Title	String	Creepers	Name of the painting
	X	int	50	Block? coordinate
	Y	int	66	Block? coordinate
	Z	int	-50	Block? coordinate
	Type	int	0	(?) Indicate which graphic to use

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 in block velocity * 32000 with regards to the speed being server ticks, 200ms

e.g. -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 (Velocity -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.

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

This command is not fully understood.

This packet is new in version 6 of the protocol, and is believed to be indication of entity damage, death and explosion

Packet ID	Field Name	Field Type	Example	Notes
0x26	Entity ID	Int	34353
	Entity Status?	Byte	0x03	Possible values: 2, 3 (entity dead?), 4, 5
	Total Size:	6 bytes

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 mob... Needs type description
Total Size:	5 bytes + Metadata

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.

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.)

A server can send a 0x32 packet prior, allowing the client to initialize the chunk. However this doesn't always happen in practice. Thus the client should initialize the chunk on-demand.

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.

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

Play Note Block (0x36)

Server to Client only

This packet is sent to the client when a note block is played. It shows the note particle being emitted from the block as well as playing the tone.

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
	Instrument Type	byte	3	The instrument type (see the table below).
	Pitch	byte	17	The pitch of the note (between 0-24 inclusive where 0 is the lowest and 24 is the highest).
Total Size:	13 bytes

Instrument Types

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

More information about how the pitch values correspond to notes in real life are available on the official Minecraft wiki.

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 array		Each record is 3 bytes, which seem to be XYZ offsets of affected blocks.
Total Size:	33 bytes + 3*(Record count) bytes

Open window (0x64)

This command is not fully understood.

This is sent to the client when it should open an inventory, such as a chest, workbench, or furnace.

Packet ID	Field Name	Field Type	Example	Notes
0x64	Window id	byte	123	The id of the window to display.
	Inventory Type	byte	2	Check below
	Window title	string	Chest	The title of the window
	Number of Slots	byte	54	Number of slots in the window (excluding the number of slots in the player inventory). For example, 3 for a furnace.
Total Size:	4 bytes + 1 string

Inventory types: 0 = basic, 1 = workbench, 2 = furnace, 3 = dispenser

Close window (0x65)

Client to Server only

This packet is sent by the client when closing a window.

Packet ID	Field Name	Field Type	Example	Notes
0x65	Window id	byte	0	This is the id of the window that was closed. (Note: Test whether this packet is sent when a chest is destroyed, or when player moves out of range.)
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 (-999 is outside of inventory)
	Right-click?	byte	1	Seems to be 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).
	Item ID	short	3	ID of Item that was in the slot or -1 if no item. If -1, this is the last field in the packet.
	Item count	byte	64	Number of items that were in the slot
	Item uses	short	10	Number of times the item was used that was in the slot
Total Size:	9 bytes (+3 for item ID != -1)

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
	Item ID	short	-1	When -1, this is the last value in this packet. -1 means no item.
	Item Count	byte	64	Number of items in a stack
	Item uses	short	3
Total Size:	6 bytes (+3 for item ID != -1)

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

Slots: [1]

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 items (see below)
	Payload	…		The payload (see below)
Total Size:	4 bytes + size of payload

This packet is a bit trickier to parse than most others because the size of its payload is variable. The payload is an array of shorts (item ID) optionally followed by a byte-short pair (count and uses) as long as the item ID does not equal -1, which signifies an empty slot.

Uses is the number of times an item has been used (the value starts at 0 and counts up.) Note that an invalid use of an item may count as 2 uses.

 offset = 0
 
 for slot in count:
     item_id = payload[offset] as short
     offset += 2
     if item_id is not equal to -1:
         count = payload[offset] as byte
         offset += 1
         uses = payload[offset] as short
         offset += 2
         inventory[slot] = new item(item_id, count, uses)
     else:
         inventory[slot] = None

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)

Server to Client only

A packet from the server indicating whether a request from the client was accepted, or whether there was a conflict (due to lag).

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

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	string	First line	First line of text in the sign
	Text2	string	Second line	Second line of text in the sign
	Text3	string	Third line	Third line of text in the sign
	Text4	string	Fourth line	Fourth line of text in the sign
Total Size:	11 bytes + 4 strings

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	string	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.

2011-1-13

• 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