Pre-release protocol

This page documents the changes from the last stable Minecraft release (currently 1.16.5, protocol 754) to the current pre-release (currently 21w07a, protocol Snapshot 15). Note that this page contains bleeding-edge information that may not be completely or correctly documented.

One 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 occurred to the respective packets there.

Contents

Data types

No changes so far.

Packets

ID	Packet name	Documentation
Play clientbound
0x05	Sculk Vibration Signal		Pre
0x05 0x06	Entity Animation (clientbound)	Current	(unchanged)
0x06 0x07	Statistics	Current	(unchanged)
0x07 0x08	Acknowledge Player Digging	Current	(unchanged)
0x08 0x09	Block Break Animation	Current	(unchanged)
0x09 0x0A	Block Entity Data	Current	(unchanged)
0x0A 0x0B	Block Action	Current	(unchanged)
0x0B 0x0C	Block Change	Current	(unchanged)
0x0C 0x0D	Boss Bar	Current	(unchanged)
0x0D 0x0E	Server Difficulty	Current	(unchanged)
0x0E 0x0F	Chat Message (clientbound)	Current	(unchanged)
0x10	Clear Titles		Pre
0x0F 0x11	Tab-Complete (clientbound)	Current	(unchanged)
0x10 0x12	Declare Commands	Current	(unchanged)
0x11	Window Confirmation (clientbound)	Current
0x12 0x13	Close Window (clientbound)	Current	(unchanged)
0x13 0x14	Window Items	Current	(unchanged)
0x14 0x15	Window Property	Current	(unchanged)
0x15 0x16	Set Slot	Current	(unchanged)
0x16 0x17	Set Cooldown	Current	(unchanged)
0x17 0x18	Plugin Message (clientbound)	Current	(unchanged)
0x18 0x19	Named Sound Effect	Current	(unchanged)
0x19 0x1A	Disconnect (play)	Current	(unchanged)
0x1A 0x1B	Entity Status	Current	(unchanged)
0x1B 0x1C	Explosion	Current	(unchanged)
0x1C 0x1D	Unload Chunk	Current	(unchanged)
0x1D 0x1E	Change Game State	Current	(unchanged)
0x1E 0x1F	Open Horse Window	Current	(unchanged)
0x20	Initialize World Border		Pre
0x1F 0x21	Keep Alive (clientbound)	Current	(unchanged)
0x20 0x22	Chunk Data	Current	Pre
0x21 0x23	Effect	Current	(unchanged)
0x22 0x24	Particle	Current	(unchanged)
0x23 0x25	Update Light	Current	Pre
0x24 0x26	Join Game	Current	(unchanged)
0x25 0x27	Map Data	Current	Pre
0x26 0x28	Trade List	Current	(unchanged)
0x27 0x29	Entity Position	Current	(unchanged)
0x28 0x2A	Entity Position and Rotation	Current	(unchanged)
0x29 0x2B	Entity Rotation	Current	(unchanged)
0x2A	Entity Movement	Current
0x2B 0x2C	Vehicle Move (clientbound)	Current	(unchanged)
0x2C 0x2D	Open Book	Current	(unchanged)
0x2D 0x2E	Open Window	Current	(unchanged)
0x2E 0x2F	Open Sign Editor	Current	(unchanged)
0x2F 0x30	Craft Recipe Response	Current	(unchanged)
0x30 0x31	Player Abilities (clientbound)	Current	(unchanged)
0x31	Combat Event	Current
0x32	End Combat Event		Pre
0x33	Enter Combat Event		Pre
0x34	Death Combat Event		Pre
0x32 0x35	Player Info	Current	(unchanged)
0x33 0x36	Face Player	Current	(unchanged)
0x36	Destroy Entities	Current
0x34 0x37	Player Position And Look (clientbound)	Current	Pre
0x35 0x38	Unlock Recipes	Current	(unchanged)
0x39	Destroy Entity		Pre
0x37 0x3A	Remove Entity Effect	Current	(unchanged)
0x38 0x3B	Resource Pack Send	Current	Pre
0x39 0x3C	Respawn	Current	(unchanged)
0x3A 0x3D	Entity Head Look	Current	(unchanged)
0x3B 0x3E	Multi Block Change	Current	(unchanged)
0x3C 0x3F	Select Advancement Tab	Current	(unchanged)
0x40	Action Bar		Pre
0x41	World Border Center		Pre
0x42	World Border Lerp Size		Pre
0x43	World Border Size		Pre
0x44	World Border Warning Delay		Pre
0x45	World Border Warning Reach		Pre
0x3E 0x46	Camera	Current	(unchanged)
0x3F 0x47	Held Item Change (clientbound)	Current	(unchanged)
0x40 0x48	Update View Position	Current	(unchanged)
0x41 0x49	Update View Distance	Current	(unchanged)
0x42 0x4A	Spawn Position	Current	Pre
0x43 0x4B	Display Scoreboard	Current	(unchanged)
0x44 0x4C	Entity Metadata	Current	(unchanged)
0x45 0x4D	Attach Entity	Current	(unchanged)
0x46 0x4E	Entity Velocity	Current	(unchanged)
0x47 0x4F	Entity Equipment	Current	(unchanged)
0x4F	Title	Current
0x48 0x50	Set Experience	Current	(unchanged)
0x49 0x51	Update Health	Current	(unchanged)
0x4A 0x52	Scoreboard Objective	Current	(unchanged)
0x4B 0x53	Set Passengers	Current	(unchanged)
0x4C 0x54	Teams	Current	(unchanged)
0x4D 0x55	Update Score	Current	(unchanged)
0x56	Set Title SubTitle		Pre
0x4E 0x57	Time Update	Current	(unchanged)
0x58	Set Title Text		Pre
0x59	Set Title Time		Pre
0x50 0x5A	Entity Sound Effect	Current	(unchanged)
0x51 0x5B	Sound Effect	Current	(unchanged)
0x52 0x5C	Stop Sound	Current	(unchanged)
0x53 0x5D	Player List Header And Footer	Current	(unchanged)
0x54 0x5E	NBT Query Response	Current	(unchanged)
0x55 0x5F	Collect Item	Current	(unchanged)
0x56 0x60	Entity Teleport	Current	(unchanged)
0x57 0x61	Advancements	Current	(unchanged)
0x58 0x62	Entity Properties	Current	Pre
0x59 0x63	Entity Effect	Current	(unchanged)
0x5A 0x64	Declare Recipes	Current	(unchanged)
0x5B 0x65	Tags	Current	Pre
Play serverbound
0x05	Client Settings	Current	Pre
Handshaking serverbound
0x00	Handshake	Current	Pre

New/modified data types

No changes so far.

Entity Metadata

Note that other entities have had metadata shifts due to these changes, not shown here.

Entity

The base class.

Index	Type	Meaning		Default
0	Byte	Bit mask	Meaning	0
		0x01	Is on fire
		0x02	Is crouching
		0x04	Unused (previously riding)
		0x08	Is sprinting
		0x10	Is swimming
		0x20	Is invisible
		0x40	has glowing effect
		0x80	Is flying with an elytra
1	VarInt	Air ticks		300
2	OptChat	Custom name		empty
3	Boolean	Is custom name visible		false
4	Boolean	Is silent		false
5	Boolean	Has no gravity		false
6	Pose	Pose		STANDING
7	VarInt	Ticks frozen in powdered snow		0

Block Actions

No changes so far.

Inventories

No changes so far.

Plugin Channels

No changes so far.

Play

Clientbound

Sculk Vibration Signal

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x05	Play	Client	Source Position	Position	Source position for the vibration.
			Destination Identifier	Identifier	Identifier of the destination codec type.
			Destination	Varies	Vanilla default destinations are a block position encoded as a Position for "block" or an entity id encoded as a VarInt for "entity".
			Arrival Ticks	VarInt	Ticks for the signal to arrive at the destination.

This packet shows a permanent particle.

Clear Titles

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x10	Play	Client
			Reset	Boolean

Initialize World Border

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x20	Play	Client	X	Double
			Z	Double
			Old Diameter	Double	Current length of a single side of the world border, in meters.
			New Diameter	Double	Target length of a single side of the world border, in meters.
			Speed	VarLong	Number of real-time milliseconds until New Diameter is reached. It appears that Notchian server does not sync world border speed to game ticks, so it gets out of sync with server lag. If the world border is not moving, this is set to 0.
			Portal Teleport Boundary	VarInt	Resulting coordinates from a portal teleport are limited to ±value. Usually 29999984.
			Warning Blocks	VarInt	In meters.
			Warning Time	VarInt	In seconds as set by /worldborder warning time.

The Notchian client determines how solid to display the warning by comparing to whichever is higher, the warning distance or whichever is lower, the distance from the current diameter to the target diameter or the place the border will be after warningTime seconds. In pseudocode:

distance = max(min(resizeSpeed * 1000 * warningTime, abs(targetDiameter - currentDiameter)), warningDistance);
if (playerDistance < distance) {
    warning = 1.0 - playerDistance / distance;
} else {
    warning = 0.0;
}

Chunk Data

Main article: Chunk Format

See also: #Unload Chunk

	The following information needs to be added to this page:
	How do biomes work now? The biome change happened at the same time as the seed change, but it's not clear how/if biomes could be computed given that it's not the actual seed... (/r/mojira discussion which notes that it seems to be some kind of interpolation, and 3D biomes are only used in the nether)

The server only sends skylight information for chunk pillars in the Overworld, it's up to the client to know in which dimension the player is currently located. You can also infer this information from the primary bitmask and the amount of uncompressed bytes sent. This packet also sends all block entities in the chunk (though sending them is not required; it is still legal to send them with Update Block Entity later).

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x20 0x22	Play	Client	Chunk X	Int	Chunk coordinate (block coordinate divided by 16, rounded down)
			Chunk Z	Int	Chunk coordinate (block coordinate divided by 16, rounded down)
			Full chunk	Boolean	See Chunk Format
			Primary Bit Mask	VarInt	Bitmask with bits set to 1 for every 16×16×16 chunk section whose data is included in Data. The least significant bit represents the chunk section at the bottom of the chunk column (from y=0 to y=15).
			Bit Mask Length	VarInt	Length of the following array
			Primary Bit Mask	Array of Long	BitSet with bits (world height in blocks / 16) set to 1 for every 16×16×16 chunk section whose data is included in Data. The least significant bit represents the chunk section at the bottom of the chunk column (from the lowest y to 15 blocks above).
			Heightmaps	NBT	Compound containing one long array named MOTION_BLOCKING, which is a heightmap for the highest solid block at each position in the chunk (as a compacted long array with 256 entries at 9 bits per entry totaling 36 longs). The Notchian server also adds a WORLD_SURFACE long array, the purpose of which is unknown, but it's not required for the chunk to be accepted.
			Biomes length	Optional VarInt	Size of the following array; should always be 1024. Not present if full chunk is false.
			Biomes	Optional Array of VarInt	1024 biome IDs, ordered by x then z then y, in 4×4×4 blocks. Not present if full chunk is false. See Chunk Format § Biomes.
			Size	VarInt	Size of Data in bytes
			Data	Byte array	See data structure in Chunk Format
			Number of block entities	VarInt	Number of elements in the following array
			Block entities	Array of NBT Tag	All block entities in the chunk. Use the x, y, and z tags in the NBT to determine their positions.

Note that the Notchian client requires an Update View Position packet when it crosses a chunk border, otherwise it'll only display render distance + 2 chunks around the chunk it spawned in.

The compacted array format has been adjusted so that individual entries no longer span across multiple longs, affecting the main data array and heightmaps.

New format, 5 bits per block, containing the following references to blocks in a palette (not shown): 122344566480743131516914101202

0020863148418841 0000000000100000100001100011000101001000010000011000100001000001
01018A7260F68C87 0000000100000001100010100111001001100000111101101000110010000111

Entity Movement

This packet may be used to initialize an entity.

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	State	Bound To	Field Name	Field Type	Notes
0x2A	Play	Client	Entity ID	VarInt

Update Light

Updates light levels for a chunk.

Packet ID	State	Bound To	Field Name		Field Type		Notes
0x23 0x25	Play	Client	Chunk X		VarInt		Chunk coordinate (block coordinate divided by 16, rounded down)
			Chunk Z		VarInt		Chunk coordinate (block coordinate divided by 16, rounded down)
			Trust Edges		Boolean		If edges should be trusted for light updates.
			Sky Light Mask		VarInt		Mask containing 18 bits, with the lowest bit corresponding to chunk section -1 (in the void, y=-16 to y=-1) and the highest bit for chunk section 16 (above the world, y=256 to y=271)
			Block Light Mask		VarInt		Mask containing 18 bits, with the same order as sky light
			Empty Sky Light Mask		VarInt		Mask containing 18 bits, which indicates sections that have 0 for all their sky light values. If a section is set in both this mask and the main sky light mask, it is ignored for this mask and it is included in the sky light arrays (the notchian server does not create such masks). If it is only set in this mask, it is not included in the sky light arrays.
			Empty Block Light Mask		VarInt		Mask containing 18 bits, which indicates sections that have 0 for all their block light values. If a section is set in both this mask and the main block light mask, it is ignored for this mask and it is included in the block light arrays (the notchian server does not create such masks). If it is only set in this mask, it is not included in the block light arrays.
			Length 1		VarInt		Length of the following array
			Sky Light Mask		Array of Long		BitSet containing bits for each sections in the world + 2 (lowest bit 16-1 blocks below min world height, highest 1-16 above max world height)
			Length 2		VarInt		Length of the following array
			Block Light Mask		Array of Long		BitSet containing bits for each sections in the world + 2, same order as sky light
			Length 3		VarInt		Length of the following array
			Empty Sky Light Mask		Array of Long		BitSet containing a variable amount of bits (see sky/block light) which indicates sections that have 0 for all their sky light values
			Length 4		VarInt		Length of the following array
			Empty Block Light Mask		Array of Long		BitSet containing a variable amount of bits (see sky/block light) which indicates sections that have 0 for all their block light values
			Sky Light array count		VarInt		Number of entries in the following array
			Sky Light arrays	Length	Array	VarInt	Length of the following array in bytes (always 2048)
				Sky Light array		Array of 2048 bytes	There is 1 array for each bit set to true in the sky light mask, starting with the lowest value. Half a byte per light value.
			Block Light array count		VarInt		Number of entries in the following array
			Block Light arrays	Length	Array	VarInt	Length of the following array in bytes (always 2048)
				Block Light array		Array of 2048 bytes	There is 1 array for each bit set to true in the block light mask, starting with the lowest value. Half a byte per light value.

Map Data

Updates a rectangular area on a map item.

Packet ID	State	Bound To	Field Name		Field Type		Notes
0x25 0x27	Play	Client	Map ID		VarInt		Map ID of the map being modified
			Scale		Byte		From 0 for a fully zoomed-in map (1 block per pixel) to 4 for a fully zoomed-out map (16 blocks per pixel)
			Tracking Position		Boolean		Specifies whether player and item frame icons are shown
			Locked		Boolean		True if the map has been locked in a cartography table
			Tracking Position		Boolean		Specifies whether player and item frame icons are shown
			Icon Count		VarInt		Number of elements in the following array. Only present if "Tracking Position" is true.
			Icon	Type	Array	VarInt enum	See below
				X		Byte	Map coordinates: -128 for furthest left, +127 for furthest right
				Z		Byte	Map coordinates: -128 for highest, +127 for lowest
				Direction		Byte	0-15
				Has Display Name		Boolean
				Display Name		Optional Chat	Only present if previous Boolean is true
			Columns		Unsigned Byte		Number of columns updated
			Rows		Optional Byte		Only if Columns is more than 0; number of rows updated
			X		Optional Byte		Only if Columns is more than 0; x offset of the westernmost column
			Z		Optional Byte		Only if Columns is more than 0; z offset of the northernmost row
			Length		Optional VarInt		Only if Columns is more than 0; length of the following array
			Data		Optional Array of Unsigned Byte		Only if Columns is more than 0; see Map item format

For icons, a direction of 0 is a vertical icon and increments by 22.5° (360/16).

Types are based off of rows and columns in map_icons.png:

Icon type	Result
0	White arrow (players)
1	Green arrow (item frames)
2	Red arrow
3	Blue arrow
4	White cross
5	Red pointer
6	White circle (off-map players)
7	Small white circle (far-off-map players)
8	Mansion
9	Temple
10	White Banner
11	Orange Banner
12	Magenta Banner
13	Light Blue Banner
14	Yellow Banner
15	Lime Banner
16	Pink Banner
17	Gray Banner
18	Light Gray Banner
19	Cyan Banner
20	Purple Banner
21	Blue Banner
22	Brown Banner
23	Green Banner
24	Red Banner
25	Black Banner
26	Treasure marker

Combat Event

Originally used for metadata for twitch streaming circa 1.8. Now only used to display the game over screen (with enter combat and end combat completely ignored by the Notchain client)

Packet ID	State	Bound To	Field Name		Field Type	Notes
0x31	Play	Client	Event		VarInt Enum	Determines the layout of the remaining packet.
			Event	Field Name
			0: enter combat	no fields	no fields
			1: end combat	Duration	VarInt	Length of the combat in ticks.
				Entity ID	Int	ID of the primary opponent of the ended combat, or -1 if there is no obvious primary opponent.
			2: entity dead	Player ID	VarInt	Entity ID of the player that died (should match the client's entity ID).
				Entity ID	Int	The killing entity's ID, or -1 if there is no obvious killer.
				Message	Chat	The death message.

End Combat Event

Unused by the Notchain client.

Packet ID	State	Bound To	Field Name		Field Type	Notes
0x32	Play	Client	Duration	VarInt	Length of the combat in ticks.
			Entity ID	Int	ID of the primary opponent of the ended combat, or -1 if there is no obvious primary opponent.

Enter Combat Event

Unused by the Notchain client.

Packet ID	State	Bound To	Field Name		Field Type	Notes
0x33	Play	Client

Death Combat Event

Used to send a respawn screen.

Packet ID	State	Bound To	Field Name		Field Type	Notes
0x34	Play	Client	Player ID	VarInt	Entity ID of the player that died (should match the client's entity ID).
			Entity ID	Int	The killing entity's ID, or -1 if there is no obvious killer.
			Message	Chat	The death message.

Player Position And Look (clientbound)

Updates the player's position on the server. This packet will also close the “Downloading Terrain” screen when joining/respawning.

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 meters, the client will be 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.

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x34 0x38	Play	Client	X	Double	Absolute or relative position, depending on Flags.
			Y	Double	Absolute or relative position, depending on Flags.
			Z	Double	Absolute or relative position, depending on Flags.
			Yaw	Float	Absolute or relative rotation on the X axis, in degrees.
			Pitch	Float	Absolute or relative rotation on the Y axis, in degrees.
			Flags	Byte	Bit field, see below.
			Teleport ID	VarInt	Client should confirm this packet with Teleport Confirm containing the same Teleport ID.
			Dismount Vehicle	Boolean	True if the player should dismount their vehicle.

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.

Field	Bit
X	0x01
Y	0x02
Z	0x04
Y_ROT	0x08
X_ROT	0x10

Destroy Entity

Sent by the server when a list of entities an entity is to be destroyed on the client.

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x36	Play	Client
			Count	VarInt	Number of elements in the following array.
			Array of VarInt	The list of entities of destroy.
			Entity ID	VarInt

Resource Pack Send

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x38 0x3B	Play	Client	URL	String (32767)	The URL to the resource pack.
			Hash	String (40)	A 40 character hexadecimal and lowercase SHA-1 hash of the resource pack file. (must be lower case in order to work) If it's not a 40 character hexadecimal string, the client will not use it for hash verification and likely waste bandwidth — but it will still treat it as a unique id
			Forced	Boolean	The notchian client will be forced to use the resource pack from the server. If they decline they will be kicked from the server.
			Forced Message	Chat	This is sent with the force resourcepack popup.

Title

Packet ID	State	Bound To	Field Name		Field Type	Notes
0x4F	Play	Client	Action		VarInt Enum
			Action	Field Name
			0: set title	Title Text	Chat
			1: set subtitle	Subtitle Text	Chat
			2: set action bar	Action bar text	Chat	Displays a message above the hotbar (the same as position 2 in Chat Message (clientbound).
			3: set times and display	Fade In	Int	Ticks to spend fading in.
				Stay	Int	Ticks to keep the title displayed.
				Fade Out	Int	Ticks to spend out, not when to start fading out.
			4: hide	no fields	no fields
			5: reset	no fields	no fields

“Hide” makes the title disappear, but if you run times again the same title will appear. “Reset” erases the text.

The title is visible on screen for Fade In + Stay + Fade Out ticks.

Action Bar

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x40	Play	Client	Action bar text	Chat	Displays a message above the hotbar (the same as position 2 in Chat Message (clientbound).

World Border Center

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x41	Play	Client	X	Double
			Z	Double

World Border Lerp Size

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x42	Play	Client	Old Diameter	Double	Current length of a single side of the world border, in meters.
			New Diameter	Double	Target length of a single side of the world border, in meters.
			Speed	VarLong	Number of real-time milliseconds until New Diameter is reached. It appears that Notchian server does not sync world border speed to game ticks, so it gets out of sync with server lag. If the world border is not moving, this is set to 0.

World Border Size

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x43	Play	Client	Diameter	Double	Length of a single side of the world border, in meters.

World Border Warning Delay

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x44	Play	Client	Warning Time	VarInt	In seconds as set by /worldborder warning time.

World Border Warning Reach

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x45	Play	Client	Warning Blocks	VarInt	In meters.

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	State	Bound To	Field Name	Field Type	Notes
0x42 0x4B	Play	Client	Location	Position	Spawn location.
			Angle	Float

Set Title SubTitle

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x56	Play	Client	Subtitle Text	Chat

Set Title Text

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x58	Play	Client	Title Text	Chat

Set Title Time

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x59	Play	Client	Fade In	Int	Ticks to spend fading in.
			Stay	Int	Ticks to keep the title displayed.
			Fade Out	Int	Ticks to spend out, not when to start fading out.

Entity Properties

Sets attributes on the given entity.

Packet ID	State	Bound To	Field Name		Field Type		Notes
0x58 0x63	Play	Client	Entity ID		VarInt
			Number Of Properties		Int VarInt		Number of elements in the following array.
			Property	Key	Array	Identifier	See below.
				Value		Double	See below.
				Number Of Modifiers		VarInt	Number of elements in the following array.
				Modifiers		Array of Modifier Data	See Attribute#Modifiers. Modifier Data defined below.

Known Key values (see also Attribute#Modifiers):

Key	Default	Min	Max	Label
generic.max_health	20.0	0.0	1024.0	Max Health.
generic.follow_range	32.0	0.0	2048.0	Follow Range.
generic.knockback_resistance	0.0	0.0	1.0	Knockback Resistance.
generic.movement_speed	0.7	0.0	1024.0	Movement Speed.
generic.attack_damage	2.0	0.0	2048.0	Attack Damage.
generic.attack_speed	4.0	0.0	1024.0	Attack Speed.
generic.flying_speed	0.4	0.0	1024.0	Flying Speed.
generic.armor	0.0	0.0	30.0	Armor.
generic.armor_toughness	0.0	0.0	20.0	Armor Toughness.
generic.attack_knockback	0.0	0.0	5.0	—
generic.luck	0.0	-1024.0	1024.0	Luck.
horse.jump_strength	0.7	0.0	2.0	Jump Strength.
zombie.spawn_reinforcements	0.0	0.0	1.0	Spawn Reinforcements Chance.
generic.reachDistance	5.0	0.0	1024.0	Player Reach Distance (Forge only).
forge.swimSpeed	1.0	0.0	1024.0	Swimming Speed (Forge only).

Unknown attributes will cause a game crash (MC-150405) due to the default minimum being larger than the default value.

Modifier Data structure:

Field Name	Field Type	Notes
UUID	UUID
Amount	Double	May be positive or negative.
Operation	Byte	See below.

The operation controls how the base value of the modifier is changed.

• 0: Add/subtract amount
• 1: Add/subtract amount percent of the current value
• 2: Multiply by amount percent

All of the 0's are applied first, and then the 1's, and then the 2's.

Tags

Packet ID	State	Bound To	Field Name		Field Type		Notes
0x5B 0x65	Play	Client
			Block Tags		(See below)		IDs are block IDs
			Item Tags		(See below)		IDs are item IDs
			Fluid Tags		(See below)		IDs are fluid IDs
			Entity Tags		(See below)		IDs are entity IDs
			Length of the array		VarInt
			Array of tags	Tag type	Array	Identifier	Tag identifier (Vanilla required tags are minecraft:block, minecraft:item, minecraft:fluid, minecraft:entity_type, and minecraft:game_event)
				Array of Tag		(See below)

Tags look like:

Field Name		Field Type		Notes
Length		VarInt		Number of elements in the following array
Tags	Tag name	Array	Identifier
	Count		VarInt	Number of elements in the following array
	Entries		Array of VarInt	Numeric ID of the given type (block, item, etc.).

Serverbound

Client Settings

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

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x05	Play	Server	Locale	String (16)	e.g. en_GB.
			View Distance	Byte	Client-side render distance, in chunks.
			Chat Mode	VarInt Enum	0: enabled, 1: commands only, 2: hidden. See processing chat for more information.
			Chat Colors	Boolean	“Colors” multiplayer setting.
			Displayed Skin Parts	Unsigned Byte	Bit mask, see below.
			Main Hand	VarInt Enum	0: Left, 1: Right.
			Disable text filtering	Boolean	Disables filtering of text on signs and written book titles. Currently always true (i.e. the filtering is disabled)

Displayed Skin Parts flags:

• Bit 0 (0x01): Cape enabled
• Bit 1 (0x02): Jacket enabled
• Bit 2 (0x04): Left Sleeve enabled
• Bit 3 (0x08): Right Sleeve enabled
• Bit 4 (0x10): Left Pants Leg enabled
• Bit 5 (0x20): Right Pants Leg enabled
• Bit 6 (0x40): Hat enabled

The most significant bit (bit 7, 0x80) appears to be unused.

Window Confirmation (serverbound)

If a confirmation sent by the client was not accepted, the server will reply with a Window Confirmation (clientbound) packet with the Accepted field set to false. When this happens, the client must send this packet to apologize (as with movement), otherwise the server ignores any successive confirmations.

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x07	Play	Server	Window ID	Byte	The ID of the window that the action occurred in.
			Action Number	Short	Every action that is to be accepted has a unique number. This number is an incrementing integer (starting at 1) with separate counts for each window ID.
			Accepted	Boolean	Whether the action was accepted.

Handshaking

Clientbound

There are no clientbound packets in the Handshaking state, since the protocol immediately switches to a different state after the client sends the first packet.

Serverbound

Handshake

This causes the server to switch into the target state.

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x00	Handshaking	Server	Protocol Version	VarInt	See protocol version numbers (currently 754 Snapshot 15)
			Server Address	String	Hostname or IP, e.g. localhost or 127.0.0.1, that was used to connect. The Notchian server does not use this information. Note that SRV records are a complete simple redirect, e.g. if _minecraft._tcp.example.com points to mc.example.org, users connecting to example.com will provide mc.example.org as server address in addition to connecting to it.
			Server Port	Unsigned Short	Default is 25565. The Notchian server does not use this information.
			Next State	VarInt Enum	1 for status, 2 for login

Status

Clientbound

No changes so far.

Serverbound

No changes so far.

Login

Clientbound

No changes so far.

Serverbound

No changes so far.