Protocol

This page presents a dissection of the new Minecraft Alpha protocol by aera (Andrew Godwin), ylt (Joe Carter) and TkTech (Tyler Kennedy). Additionally, credit goes to the citizens of #mcc 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)

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.

Client to Server Packets

Keep Alive (0x00)

This packet may be sent by the client 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 server will disconnect a client if it doesn't receive at least one packet before it increments a variable 1200 times.

Packet ID
0x00

Login Request (0x01)

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	4	The latest version of the protocol is 5
	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

Handshake (0x02)

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

Chat Message (0x03)

The 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 short with the length of the message is prepended to the text sent. eg: 1 byte header [0x03], 2 byte short [string length], N byte string

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

Player Inventory (0x05)

Sent by the client whenever the inventory is modified (item destruction, pickup, crafting, etc…). For details, see here.

Packet ID	Field Name	Field Type	Example	Notes
0x05	Type	int	-1	The “type” of inventory being sent (see here)
	Count	short	4	The number of inventory items (see here)
	Payload	…		The payload (see here)
Total Size:	7 bytes + size of payload

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
	Punching?	bool	true	Seems to be true when the player is punching/slashing a mob, otherwise false.
Total Size:	10 bytes

Respawn (0x09)

Sent by the client when the player presses the 'respawn' button after dying. The server then drops the player's inventory and teleports the user to the spawn point.

Packet ID
0x09
Total Size: 1 bytes.

Player (0x0A)

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)

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)

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).

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

Player Position & Look (0x0D)

A combination of Player Look and Player position.

Packet ID	Field Name	Field Type	Example	Notes
0x0D	X	double	6.5	Absolute position
	Y	double	67.240000009536743	Absolute position
	Stance	double	65.620000004768372	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

When the server sends this packet to the client, the Stance and Y are swapped, see server Player Position & Look packet.

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

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	Block or Item ID	short	1	The block or item to be placed
	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)
Total Size:	13 bytes

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. (Unverified?)

Holding Change (0x10)

Sent when the player changes the item or block currently being held.

Packet ID	Field Name	Field Type	Example	Notes
0x10	Unused	int	6341424	Unused when sent from a client, can be any random value
	Block or Item ID	short	1	The block/item to be equipped
Total Size:	7 bytes

Arm Animation (0x12)

Sent whenever someone swings their arm.

Packet ID	Field Name	Field Type	Example	Notes
0x12	EID	int	55534	Player ID
	Animate	bool	1	If true, animate the arm
Total Size:	6 bytes

Pickup Spawn (0x15)

A pickup spawn is sent from the client to the server whenever the client drops an item they are holding. This identical to the pickup spawn packet that is sent from the server to the client.

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
	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:	23 bytes

Disconnect (0xFF)

Sent by the client when it's doing a clean disconnect.

Packet ID	Field Name	Field Type	Example	Notes
0xFF	Reason	string	Quitting	The server doesn't appear to do anything with this (yet)
Total Size:	3 bytes + length of strings

Server To Client Packets

Keep Alive (0x00)

This packet may be sent by the server to keep the connection alive, or may be a relic of UDP testing. No one is really sure.

Packet ID
0x00

Login Response (0x01)

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
	Dimension	byte	0	Used for specifying the players dimension -1 for hell, 0 otherwise
Total Size:	18 bytes + length of strings

Handshake (0x02)

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.

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 formatted chat message from the server. Note that it is unreliable to parse chat when it's sent from the server → client as each server can/will format it differently (some use <,> others use [,], etc…)

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)

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 minutes
Total Size:	9 bytes

Player Inventory (0x05)

Sent by the server to set or reset a players inventory. This includes the main inventory, equipped armour and crafting slots. Packets for all three types are sent to initialize the players inventory before spawning them.

Packet ID	Field Name	Field Type	Example	Notes
0x05	Type	int	-1	The “type” of inventory being sent (see below)
	Count	short	4	The number of inventory items (see below)
	Payload	…		The payload (see below)
Total Size:	7 bytes + size of payload

Type can (currently) be one of three values:

Inventory Type	Value	Count
Main inventory	-1	36
Equipped armour	-2	4
Crafting slots	-3	4

This packet is a bit more tricky 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 health) as long as the item ID does not equal -1, which signifies an empty slot.

 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
         health = payload[offset] as short
         offset += 2
         inventory[slot] = new item(item_id, count, health)
     else:
         inventory[slot] = None

Spawn Position (0x06)

Sent by the server after login to specify the players starting location and to initialize compasses. It can be sent at any time afterwords to update the point compasses are focused on.

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

Update Health (0x08)

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	byte	20	0 = dead, 20 = full HP
Total Size:	2 bytes

Respawn (0x09)

Sent by the server after receiving a respawn packet from the client. The client will not leave the respawn screen it seems until this packet is received.

Packet ID
0x09

Player Position & Look (0x0D)

A combination of Player Look and Player position.

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

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.

Holding Change (0x10)

Sent when the player changes the item or block currently being held.

Packet ID	Field Name	Field Type	Example	Notes
0x10	EID?	int	6341424	Player EID?
	Block or Item ID	short	1	The block/item to be equipped
Total Size:	7 bytes

Add To Inventory (0x11)

Sent by the server when a player has become close enough to collect an item on the ground.

Packet ID	Field Name	Field Type	Example	Notes
0x11	Item Type	short	5
	Count	byte	10
	Life	short	0
Total Size:	6 bytes

“Life” can range from 0x01 (full health) to 0x32 (no health), 0x00 omits the health bar altogether, and is what should be used for blocks.

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) or 2 (death animation?). Getting 102 somewhat often, too.
Total Size:	6 bytes

Named Entity Spawn (0x14)

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 whenever an item on the ground (say a pickaxe thrown on the ground) comes into range of the player.

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
	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:	23 bytes

Collect Item (0x16)

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 (0x11 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)

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

Mob Spawn (0x18)

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
Total Size:	20 bytes

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)

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)

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)

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.

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

Entity Look (0x20)

This packet is sent by the server when an entity rotates.

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)

This packet is sent by the server when an entity rotates and moves.

Packet ID	Field Name	Field Type	Example	Notes
0x21	EID	int	459	Entity ID
	X	byte	1	X axis Relative movement as an Absolute Integer
	Y	byte	-7	Y axis Relative movement as an Absolute Integer
	Z	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)

This packet is sent by the server when an entity moves more then 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

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

Pre-Chunk (0x32)

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)

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 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.

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.

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

Complex Entities (0x3B)

This is a complex packet used to send entities including their entire NBT representation. This packet is currently used for furnaces, chests, signs and mob spawners. This packet is only temporary, and used for rapid prototyping of new types of entities. Specialized packets for each object will eventually be added.

Packet ID	Field Name	Field Type	Example	Notes
0x3B	X	int	32	Entity X in block coordinates
	Y	short	64	Entity Y in block coordinates
	Z	int	32	Entity Z in block coordinates
	Payload Size	short	84	The size (in bytes) of the payload
	Payload	byte array	…	The payload is a compressed (GZ) NBT file
Total Size:	13 bytes + payload

Kick (0xFF)

Sent by the server before it disconnects a client.

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.

2010-11-24

• Protocol version changed to 5
• Packet 0x08 (Update Health) added
• Packet 0x09 (Respawn) 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