Pre-release protocol

This page documents the changes from release 1.21.1 (protocol 767) to the current release (1.21.3, protocol 768). The stable protocol documentation is currently lagging behind, and the changes documented here will be merged soon, once they are complete. The current pre-release (snapshot 24w44a) is not yet 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

Name	Size (bytes)	Encodes	Notes
ID Set	Varies	Set of registry IDs specified either inline or as a reference to a tag.	See #ID Set

ID Set

Represents a set of IDs in a certain registry (implied by context), either directly (enumerated IDs) or indirectly (tag name).

Name	Type	Description
Type	VarInt	Identifier used to determine the data that follows. It can be either: 0 - Represents a named set of IDs defined by a tag. Anything else - Represents an ad-hoc set of IDs enumerated inline.
Tag Name	Optional Identifier	The registry tag defining the ID set. Only present if Type is 0.
IDs	Optional Array of VarInt	An array of registry IDs. Only present if Type is not 0. The size of the array is equal to Type - 1.

Packets

ID	Packet name	Documentation
Play clientbound
0x20	Synchronize Entity Position		Pre
0x31	Move Minecart Along Track		Pre
0x41	Update Recipe Book	Current
0x43	Player Rotation		Pre
0x44	Recipe Book Add		Pre
0x45	Recipe Book Remove		Pre
0x46	Recipe Book Settings		Pre
0x53 0x63	Set Held Item	Current	(unchanged)
0x5a	Set Cursor Item		Pre
0x66	Set Player Inventory Slot		Pre
Play serverbound
0x02	Bundle Item Selected		Pre
0x0b	Client Tick End		Pre

Handshake

No changes so far.

Status

No changes so far.

Login

No changes so far.

Configuration

No changes so far.

Play

Clientbound

Synchronize Entity Position

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x20	Play	Client	Entity ID	VarInt
			X	Double
			Y	Double
			Z	Double
			Velocity X	Double
			Velocity Y	Double
			Velocity Z	Double
			Yaw	Float	Rotation on the X axis, in degrees.
			Pitch	Float	Rotation on the Y axis, in degrees.
			On Ground	Boolean

Move Minecart Along Track

Packet ID	State	Bound To	Field Name		Field Type		Notes
0x31	Play	Client	Entity ID		VarInt
			Step Count		VarInt		Number of elements in the following array.
			Steps	X	Array	Double
				Y		Double
				Z		Double
				Velocity X		Double
				Velocity Y		Double
				Velocity Z		Double
				Yaw		Angle
				Pitch		Angle
				Weight		Float

Player Rotation

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x43	Play	Client	Yaw	Float	Rotation on the X axis, in degrees.
			Pitch	Float	Rotation on the Y axis, in degrees.

Recipe Book Add

Packet ID	State	Bound To	Field Name		Field Type		Notes
0x44	Play	Client	Recipe Count		VarInt		Number of elements in the following array.
			Recipes	Recipe ID	Array	VarInt	ID to assign to the recipe.
				Display ID		VarInt	ID in the minecraft:recipe_display registry.
				Group ID		VarInt
				Category ID		VarInt	ID in the minecraft:recipe_book_category registry.
				Has Ingredients		Boolean
				Ingredient Count		Optional VarInt	Number of elements in the following array. Only present if Has Ingredients is true.
				Ingredients		Optional Array of ID Set	Only present if Has Ingredients is true.
			Flags		Byte		0x01: show notification; 0x02: highlight as new

Recipe Book Remove

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x45	Play	Client	Recipe Count	VarInt	Number of elements in the following array.
			Recipes	Array of VarInt	IDs of recipes to remove.

Recipe Book Settings

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x46	Play	Client	Crafting Recipe Book Open	Boolean	If true, then the crafting recipe book will be open when the player opens its inventory.
			Crafting Recipe Book Filter Active	Boolean	If true, then the filtering option is active when the players opens its inventory.
			Smelting Recipe Book Open	Boolean	If true, then the smelting recipe book will be open when the player opens its inventory.
			Smelting Recipe Book Filter Active	Boolean	If true, then the filtering option is active when the players opens its inventory.
			Blast Furnace Recipe Book Open	Boolean	If true, then the blast furnace recipe book will be open when the player opens its inventory.
			Blast Furnace Recipe Book Filter Active	Boolean	If true, then the filtering option is active when the players opens its inventory.
			Smoker Recipe Book Open	Boolean	If true, then the smoker recipe book will be open when the player opens its inventory.
			Smoker Recipe Book Filter Active	Boolean	If true, then the filtering option is active when the players opens its inventory.

Set Cursor Item

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x5A	Play	Client	Slot Data	Slot

Set Player Inventory Slot

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x66	Play	Client	Slot	VarInt
			Slot Data	Slot

Serverbound

Bundle Item Selected

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x02	Play	Server	Slot of Bundle	VarInt
			Slot in Bundle	VarInt

Client Tick End

Packet ID	State	Bound To	Field Name	Field Type	Notes
0x0B	Play	Server	no fields