Pre-release protocol

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

Protocol History

14w04b

• Spawn Painting now uses the 'Position' data type
• Changed Spawn Painting's Direction type to Unsigned Byte

14w04a

• Encoding for 'Position' changed

Clientbound

• Changed Entity Equipment's EntityId type to VarInt
• Changed Update Health's Food type to VarInt
• Changed Use Bed's EntityId type to VarInt
• Added new fields to Spawn Player
• Changed Collect Item's EntityId(s) types to VarInt
• Changed Entity Velocity's EntityId type to VarInt
• Changed Destroy Entities' Length type to VarInt
• Changed Destroy Entities' EntityIds type to VarInt array
• Changed Entity's EntityId type to VarInt
• Changed Entity Teleport's EntityId type to VarInt
• Changed Entity Head Look's EntityId type to VarInt
• Changed Entity Metadata's EntityId type to Varint
• Changed Entity Effect's EntityId type to VarInt
• Changed Entity Effect's Duration type to VarInt
• Changed Remove Entity Effect's EntityId type to VarInt
• Changed Set Experience's Level type to VarInt
• Changed Set Experience's Total Experience type to VarInt
• Changed Entity Properties's EntityId type to VarInt
• Changed Entity Properties's List Length type to VarInt
• Changed Player List Item's Ping type to VarInt
• Changed Update Score's Value type to VarInt
• Changed Teams' Player count type to VarInt
• New packet 'Combat Event'

Serverbound

• Changed Keep Alive's Keep Alive ID type to VarInt
• Changed Use Entity's Target type to VarInt
• Changed Use Entity's Mouse type to Unsigned Byte
• Removed everything from Animation
• Changed Entity Action's EntityId type to VarInt
• Changed Entity Action's Action ID type to Unsigned Byte
• Changed Entity Action's Jump Boast type to VarInt
• Merged Steer Vehicle's Jump and Unmount into a Bit Field
• Changed Client Status's Action ID type to Unsigned Byte

14w03a

• New data type 'Position'

Clientbound

• Spawn Position now uses the 'Position' data type
• Use Bed now uses the 'Position' data type
• Block Change now uses the 'Position' data type
• Block Action now uses the 'Position' data type
• Block Break Animation now uses the 'Position' data type
• Effect now uses the 'Position' data type
• Sign Update now uses the 'Position' data type
• Update Block Entity now uses the 'Position' data type
• Sign Editor Open nows uses the 'Position' data type

Serverbound

• Player Digging now uses the 'Position' data type
• Player Block Placement now uses the 'Position' data type
• Update Sign now uses the 'Position' data type
• Client Settings 'show cape' type changed from boolean to unsigned byte

14w02a

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

Protocol Version

Version	Protocol
14w02a	5
14w03a	6
14w04a	7
14w04b	8

New data types

Position

A single long split up as followed:

0xFFFFFFF000000000 - X

0x0000000FF0000000 - Y

0x000000000FFFFFFF - Z

Play

Clientbound

Chat Message

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

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

Malformed JSON will disconnect the client

Entity Equipment

Packet ID	Field Name	Field Type	Notes
0x04	EntityID	VarInt	Entity's ID
	Slot	Short	Equipment slot: 0=held, 1-4=armor slot (1 - boots, 2 - leggings, 3 - chestplate, 4 - helmet)
	Item	Slot	Item in slot format

Spawn Position

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	Notes
0x05	Location	Position	Spawn location

Update Health

Sent by the server to update/set the health of the player it is sent to.

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	Notes
0x06	Health	Float	0 or less = dead, 20 = full HP
	Food	VarInt	0 - 20
	Food Saturation	Float	Seems to vary from 0.0 to 5.0 in integer increments

Player Position And Look

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

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

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

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

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

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

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

About the flags field:

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

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

Use Bed

This packet tells that a player goes to bed.

The client with the matching Entity ID will go into bed mode.

This Packet is sent to all nearby players including the one sent to bed.

Packet ID	Field Name	Field Type	Notes
0x0A	Entity ID	VarInt	Player ID
	Location	Position	Block location of the head part of the bed

Spawn Player

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.

Packet ID	Field Name		Field Type	Notes
0x0C	Entity ID		VarInt	Player's Entity ID
	Player UUID		String	Player's UUID
	Player Name		String	Player's Name
	Data length		VarInt
	Data	Name	String	Name of the property as return by the session server's /hasJoined. E.g: textures
		Value	String	Value of the property (base64) as return by the session server's /hasJoined
		Signature	String	Signature of the property (base64) as return by the session server's /hasJoined.
	X		Int	Player X as a Fixed-Point number
	Y		Int	Player X as a Fixed-Point number
	Z		Int	Player X as a Fixed-Point number
	Yaw		Byte	Player rotation as a packed byte
	Pitch		Byte	Player rotation as a packet byte
	Current Item		Short	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.
	Metadata		Metadata	The client will crash if no metadata is sent

The client will crash if no metadata is sent The client will disconnect if both UUID and Name are empty

Collect Item

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, and it doesn't add it to your inventory. 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	Notes
0x0D	Collected Entity ID	VarInt
	Collector Entity ID	VarInt

Spawn Painting

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

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)

Packet ID	Field Name	Field Type	Notes
0x10	Entity ID	VarInt	Entity's ID
	Title	String	Name of the painting. Max length 13
	Location	Position	Center coordinates
	Direction	Unsigned Byte	Direction the painting faces (0 -z, 1 -x, 2 +z, 3 +x)

Entity Velocity

Velocity is believed to be in units of 1/8000 of a block per server tick (50ms); for example, -1343 would move (-1343 / 8000) = −0.167875 blocks per tick (or −3,3575 blocks per second).

Packet ID	Field Name	Field Type	Notes
0x12	Entity ID	VarInt	Entity's ID
	Velocity X	Short	Velocity on the X axis
	Velocity Y	Short	Velocity on the Y axis
	Velocity Z	Short	Velocity on the Z axis

Destroy Entities

Sent by the server when an list of Entities is to be destroyed on the client.

Packet ID	Field Name	Field Type	Notes
0x13	Count	VarInt	Length of following array
	Entity IDs	Array of VarInt	The list of entities of destroy

Entity

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	Notes
0x14	Entity ID	VarInt	Entity's ID

Entity Teleport

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

Packet ID	Field Name	Field Type	Notes
0x18	Entity ID	VarInt	Entity's ID
	X	Int	X position as a Fixed-Point number
	Y	Int	Y position as a Fixed-Point number
	Z	Int	Z position as a Fixed-Point number
	Yaw	Byte	The X Axis rotation as a fraction of 360
	Pitch	Byte	The Y Axis rotation as a fraction of 360

Entity Head Look

Changes the direction an entity's head is facing.

Packet ID	Field Name	Field Type	Notes
0x19	Entity ID	VarInt	Entity's ID
	Head Yaw	Byte	Head yaw in steps of 2p/256

Entity Metadata

Packet ID	Field Name	Field Type	Notes
0x1C	Entity ID	VarInt	Entity's ID
	Metadata	Metadata

Entity Effect

Packet ID	Field Name	Field Type	Notes
0x1D	Entity ID	VarInt	Entity's ID
	Effect ID	Byte	See [[1]]
	Amplifier	Byte
	Duration	VarInt

Remove Entity Effect

Packet ID	Field Name	Field Type	Notes
0x1E	Entity ID	VarInt	Entity's ID
	Effect ID	Byte

Set Experience

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

Packet ID	Field Name	Field Type	Notes
0x1F	Experience bar	Float	Between 0 and 1
	Level	VarInt
	Total Experience	VarInt

Entity Properties

Packet ID	Field Name	Field Type	Notes
0x20	Entity ID	VarInt	Entity's ID
	Count	Int	Length of following array
	Properties	Array of Property Data

Property Data structure:

Field Name	Field Type	Notes
Key	String
Value	Double
List Length	VarInt	Number of list elements that follow.
Modifiers	Array of Modifier Data	http://www.minecraftwiki.net/wiki/Attribute#Modifiers

Known key values:

Key	Default	Min	Max	Label
generic.maxHealth	20.0	0.0	Double.MaxValue	Max Health
generic.followRange	32.0	0.0	2048.0	Follow Range
generic.knockbackResistance	0.0	0.0	1.0	Knockback Resistance
generic.movementSpeed	0.699999988079071	0.0	Double.MaxValue	Movement Speed
generic.attackDamage	2.0	0.0	Double.MaxValue
horse.jumpStrength	0.7	0.0	2.0	Jump Strength
zombie.spawnReinforcements	0.0	0.0	1.0	Spawn Reinforcements Chance

Modifier Data structure:

Field Name	Field Type	Notes
UUID	128-bit integer
Amount	Double
Operation	Byte

Block Change

Packet ID	Field Name	Field Type	Notes
0x23	Location	Position	Block Coordinates
	Block ID	VarInt	The new block ID for the block
	Block Metadata	Unsigned Byte	The new metadata for the block

Block Action

This packet is used for a number of things:

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

See Also: Block Actions

Packet ID	Field Name	Field Type	Notes
0x24	Location	Position	Block Coordinates
	Byte 1	Unsigned Byte	Varies depending on block - see Block_Actions
	Byte 2	Unsigned Byte	Varies depending on block - see Block_Actions
	Block Type	VarInt	The block type for the block

Block Break Animation

0-9 are the displayable destroy stages and each other number means that there is no animation on this coordinate.

You can also set an animation to air! The animation will still be visible.

If you need to display several break animations at the same time you have to give each of them a unique Entity ID.

Also if you set the coordinates to a special block like water etc. it won't show the actual break animation but some other interesting effects. (Water will loose it's transparency)

Packet ID	Field Name	Field Type	Notes
0x25	Entity ID	VarInt	Entity's ID
	Location	Position	Block Position
	Destroy Stage	Byte	0 - 9

Effect

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

By default, the minecraft client adjusts the volume of sound effects based on distance. The final boolean field is used to disable this, and instead the effect is played from 2 blocks away in the correct direction. Currently this is only used for effect 1013 (mob.wither.spawn), and is ignored for any other value by the client.

Packet ID	Field Name	Field Type	Notes
0x28	Effect ID	Int	The ID of the effect, see below.
	Location	Position	The location of the effect
	Data	Int	Extra data for certain effects, see below.
	Disable relative volume	Bool	See above

Effects

ID	Name
Sound
1000	random.click
1001	random.click
1002	random.bow
1003	random.door_open or random.door_close (50/50 chance)
1004	random.fizz
1005	Play a music disc. Data Record ID
(1006 not assigned)
1007	mob.ghast.charge
1008	mob.ghast.fireball
1009	mob.ghast.fireball, but with a lower volume.
1010	mob.zombie.wood
1011	mob.zombie.metal
1012	mob.zombie.woodbreak
1013	mob.wither.spawn
1014	mob.wither.shoot
1015	mob.bat.takeoff
1016	mob.zombie.infect
1017	mob.zombie.unfect
1018	mob.enderdragon.end
1020	random.anvil_break
1021	random.anvil_use
1022	random.anvil_land
Particle
2000	Spawns 10 smoke particles, e.g. from a fire. Data direction, see below
2001	Block break. Data Block ID
2002	Splash potion. Particle effect + glass break sound. Data Potion ID
2003	Eye of ender entity break animation - particles and sound
2004	Mob spawn particle effect: smoke + flames
2005	Spawn "happy villager" effect (green crosses), used for bonemealing vegetation.

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

Open Window

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

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

See inventory windows for further information.

Update Sign

This message is sent from the server to the client whenever a sign is discovered or created. This message is NOT sent when a sign is destroyed or unloaded.

Packet ID	Field Name	Field Type	Notes
0x33	Location	Position	Block Coordinates
	Line 1	String	First line of text in the sign
	Line 2	String	Second line of text in the sign
	Line 3	String	Third line of text in the sign
	Line 4	String	Fourth line of text in the sign

Update Block Entity

Essentially a block update on a block entity.

Packet ID	Field Name	Field Type	Notes
0x35	Location	Position
	Action	Unsigned Byte	The type of update to perform
	Data length	Short	Varies
	NBT Data	Byte Array	Present if data length > 0. Compressed with gzip. Varies

Actions

• 1: Set mob displayed inside a mob spawner. Custom 1 contains the mob type

Sign Editor Open

Sent on placement of sign.

Packet ID	Field Name	Field Type	Notes
0x36	Location	Position	Block coordinates

Player List Item

Sent by the notchian server to update the user list (<tab> in the client).

Packet ID	Field Name	Field Type	Notes
0x38	Player name	String	Supports chat colouring, limited to 16 characters.
	Online	Bool	The client will remove the user from the list if false.
	Ping	VarInt	Ping, presumably in ms.

Update Score

This is sent to the client when it should update a scoreboard item.

Packet ID	Field Name	Field Type	Notes
0x3C	Item Name	String	An unique name to be displayed in the list.
	Update/Remove	Byte	0 to create/update an item. 1 to remove an item.
	Score Name	String	The unique name for the scoreboard to be updated. Only sent when Update/Remove does not equal 1.
	Value	VarInt	The score to be displayed next to the entry. Only sent when Update/Remove does not equal 1.

The final String and Int are only sent if the Update/Remove Byte does not equal 1

Teams

Creates and updates teams.

Packet ID	Field Name	Field Type	Notes
0x3E	Team Name	String	A unique name for the team. (Shared with scoreboard).
	Mode	Byte	If 0 then the team is created. If 1 then the team is removed. If 2 the team team information is updated. If 3 then new players are added to the team. If 4 then players are removed from the team.
	Team Display Name	String	Only if Mode = 0 or 2.
	Team Prefix	String	Only if Mode = 0 or 2. Displayed before the players' name that are part of this team.
	Team Suffix	String	Only if Mode = 0 or 2. Displayed after the players' name that are part of this team.
	Friendly fire	Byte	Only if Mode = 0 or 2; 0 for off, 1 for on, 3 for seeing friendly invisibles
	Player count	VarInt	Only if Mode = 0 or 3 or 4. Number of players in the array
	Players	Array of strings	Only if Mode = 0 or 3 or 4. Players to be added/remove from the team.

Server Difficulty

Changes the difficulty setting in the client's option menu

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

Combat Event

Packet ID	Field Name	Field Type	Notes
0x42	Event	Unsigned Byte	0 ENTER_COMBAT, 1 END_COMBAT, 2 ENTITY_DEAD
	Duration	VarInt	Only for END_COMBAT
	Entity ID	Int	Only for END_COMBAT
	Player ID	VarInt	Only for ENTITY_DEAD
	Entity ID	Int	Only for ENTITY_DEAD
	Message	String	Only for ENTITY_DEAD

Serverbound

Keep Alive

The server will frequently send out a keep-alive, each containing a random ID. The client must respond with the same packet.

Packet ID	Field Name	Field Type	Notes
0x00	Keep Alive ID	VarInt

Use Entity

This packet is sent from the client to the server when the client attacks or right-clicks another entity (a player, minecart, etc).

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.

Note that middle-click in creative mode is interpreted by the client and sent as a Creative Inventory Action packet instead.

Packet ID	Field Name	Field Type	Notes
0x02	Target	VarInt
	Mouse	Unsigned Byte	0 = Left-click, 1 = Right-click

Player Digging

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	Notes
0x07	Status	Byte	The action the player is taking against the block (see below)
	Location	Position	Block position
	Face	Byte	The face being hit (see below)

Status can (currently) be one of six values:

Meaning	Value
Started digging	0
Cancelled digging	1
Finished digging	2
Drop item stack	3
Drop item	4
Shoot arrow / finish eating	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, the client simply send a 1 (Cancel 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. Status code 3 is similar, but drops the entire stack.

Status code 5 (shoot arrow / finish eating) is also a special case. The x, y and z fields are all set to 0 like above, with the exception of the face field, which is set to 255.

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

Packet ID	Field Name	Field Type	Notes
0x08	Location	Position	Block position
	Direction	Byte	The offset to use for block/item placement (see below)
	Held item	Slot
	Cursor position X	Byte	The position of the crosshair on the block
	Cursor position Y	Byte
	Cursor position Z	Byte

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. (Note that Y is unsigned so set to 255.) 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. The client has been observed (1.2.5 and 1.3.2) to send both real item IDs and -1 in a single session.

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.

Animation

Packet ID	Field Name	Field Type	Notes
0x0A

Entity Action

Sent at least when crouching, leaving a bed, or sprinting. To send action animation to client use 0x28. The client will send this with Action ID = 3 when "Leave Bed" is clicked.

Packet ID	Field Name	Field Type	Notes
0x0B	Entity ID	VarInt	Player ID
	Action ID	Unsigned Byte	The ID of the action, see below.
	Jump Boost	VarInt	Horse jump boost. Ranged from 0 -> 100.

Action ID can be one of the following values:

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

Steer Vehicle

Packet ID	Field Name	Field Type	Notes
0x0C	Sideways	Float	Positive to the left of the player
	Forward	Float	Positive forward
	Flags	Unsigned Byte	0x1 Jump, 0x2 Unmount

Update Sign

This message is sent from the client to the server when the "Done" button is pushed after placing a sign.

Packet ID	Field Name	Field Type	Notes
0x12	Location	Position	Block Coordinates
	Line 1	String	First line of text in the sign
	Line 2	String	Second line of text in the sign
	Line 3	String	Third line of text in the sign
	Line 4	String	Fourth line of text in the sign

Client Settings

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

Packet ID	Field Name	Field Type	Notes
0x15	Locale	String	en_GB
	View distance	Byte	0-3 for 'far', 'normal', 'short', 'tiny'.
	Chat flags	Byte	Chat settings. See notes below.
	Chat colours	Bool	"Colours" multiplayer setting
	Displayed skin parts	Unsigned Byte	Unknown

Chat flags has several values packed into one byte.

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

Client Status

Sent when the client is ready to complete login and when the client is ready to respawn after death.

Packet ID	Field Name	Field Type	Notes
0x16	Action ID	Unsigned Byte	See below

Action ID values:

Action ID	Name
0	Perform respawn
1	Request stats
2	Open inventory achievement