Sending Packets

This page covers how to manually send raw packets to clients using the PlayerConnection API. This is an experimental feature for advanced use cases where you need to send data that FourKit doesnt yet wrap in its API.

This API is experimental and may change. You are responsible for constructing valid packets!!! malformed data can crash or disconnect the client.

Also please keep in mind, some of this info may not be accurate! Feel free to improve this by contributing on the Github.

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Overview

Every Minecraft packet on the wire looks like this:

Field	Size	Description
Size	4 bytes (big-endian)	Total length of the remaining data (packet ID + payload). Written automatically by the server.. you do NOT include it.
Packet ID	1 byte	Which packet this is. Only the low byte matters on the wire even though IDs are int in source.
Payload	variable	The rest of the packet data, format depends on the packet ID.

When you call PlayerConnection.send(byte[] data), the server prepends the 4-byte big-endian size header for you. Your byte array should start with the packet ID byte followed by the payload.

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Wire Data Types

All multi-byte values are big-endian (most significant byte first).

Type	Size	Description
byte	1	Unsigned 8-bit integer (0-255).
bool	1	0 = false, non-zero = true.
short	2	Signed 16-bit integer.
int	4	Signed 32-bit integer.
long	8	Signed 64-bit integer.
float	4	IEEE 754 single-precision float.
utf	2 + n	Modified UTF-8 string: short byte-length prefix followed by that many bytes of data. See String Encoding.
item	variable	Item data (item ID, count, damage). See Item Data.
metadata	variable	Entity metadata (SynchedEntityData). See Metadata Encoding.

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String Encoding

Strings use modified UTF-8 encoding:

1. A short (2 bytes, big-endian) containing the byte length of the string data.
2. That many bytes of modified-UTF8 characters.

For most ASCII text (chat messages, names, etc.) this is identical to standard UTF-8. A helper to write a string:

static int WriteUTF(byte[] buffer, int offset, string text)
{
    byte[] utf8 = System.Text.Encoding.UTF8.GetBytes(text);
    WriteShort(buffer, offset, (short)utf8.Length);
    Buffer.BlockCopy(utf8, 0, buffer, offset + 2, utf8.Length);
    return 2 + utf8.Length; // total bytes written
}

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Item Data

Several container packets include serialized item data. The wire format for a single item slot is:

Field	Type	Description
id	short	Item ID. -1 means the slot is empty (no further fields follow).
count	byte	Stack size.
damage	short	Damage/metadata value.

If the item ID is -1, only the short is written (2 bytes for an empty slot). Otherwise all three fields are written (5 bytes).

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Metadata Encoding (SynchedEntityData)

Entity metadata is used in packets like AddMobPacket (24), AddPlayerPacket (20), and SetEntityDataPacket (40). It's a list of typed key-value entries terminated by 0x7F.

Each entry starts with a 1-byte header:

• Bits 5-7 (mask 0xE0): Type ID, shifted right by 5.
• Bits 0-4 (mask 0x1F): Data slot ID (max 31).

So the header byte is (type << 5) | (id & 0x1F).

The value immediately follows, sized based on the type:

Type ID	Name	Value Size
0	Byte	1 byte
1	Short	2 bytes
2	Int	4 bytes
3	Float	4 bytes
4	String	utf (2-byte length prefix + string data)
5	ItemInstance	item (see Item Data)

After all entries, write 0x7F as the EOF marker.

Common Data Slot IDs

These are the data slot IDs used by the entity class hierarchy. When constructing metadata, define these in order and use the correct type.

Entity (base):

ID	Type	Name	Description
0	Byte	DATA_SHARED_FLAGS	Bitfield: bit 0=on fire, 1=sneaking, 3=sprinting, 4=using item, 5=invisible, 6=idle anim
1	Short	DATA_AIR_SUPPLY	Air supply (default 300, max 300)

LivingEntity:

ID	Type	Name	Description
6	Float	DATA_HEALTH	Health value (default 1.0)
7	Int	DATA_EFFECT_COLOR	Potion effect color (default 0)
8	Byte	DATA_EFFECT_AMBIENCE	Potion effect ambience (default 0)
9	Byte	DATA_ARROW_COUNT	Number of arrows stuck in entity (default 0)

Mob:

ID	Type	Name	Description
10	String	DATA_CUSTOM_NAME	Custom name tag (default "")
11	Byte	DATA_CUSTOM_NAME_VISIBLE	Show name tag (0 or 1, default 0)

For example, to write metadata for a basic mob with a custom name:

// helper to write a metadata entry header
static void WriteMetaHeader(byte[] buffer, int offset, int type, int id)
{
    buffer[offset] = (byte)((type << 5) | (id & 0x1F));
}
 
// build metadata for a mob with a visible custom name "booty"
// enity base: flags=0, air=300
// livingentity: health=20.0, effectColor=0, effectAmbience=0, arrowCount=0
// mob: customName="booty", customNameVisible=1
 
byte[] nameBytes = System.Text.Encoding.UTF8.GetBytes("booty");
int metaSize = (1+1) + (1+2) + (1+4) + (1+4) + (1+1) + (1+1)
             + (1 + 2 + nameBytes.Length) + (1+1) + 1; // +1 for EOF
byte[] meta = new byte[metaSize];
int pos = 0;
 
// Entity
WriteMetaHeader(meta, pos, 0, 0); pos++; meta[pos++] = 0; // flags = 0
WriteMetaHeader(meta, pos, 1, 1); pos++; WriteShort(meta, pos, 300); pos += 2; // air supply
 
// LivingEntity
WriteMetaHeader(meta, pos, 3, 6); pos++; WriteFloat(meta, pos, 20.0f); pos += 4; // health
WriteMetaHeader(meta, pos, 2, 7); pos++; WriteInt(meta, pos, 0); pos += 4; // effect color
WriteMetaHeader(meta, pos, 0, 8); pos++; meta[pos++] = 0; // effect ambience
WriteMetaHeader(meta, pos, 0, 9); pos++; meta[pos++] = 0; // arrow count
 
// Mob
WriteMetaHeader(meta, pos, 4, 10); pos++;
pos += WriteUTF(meta, pos, "booty"); // custom name
WriteMetaHeader(meta, pos, 0, 11); pos++; meta[pos++] = 1; // name visible
 
meta[pos] = 0x7F; // EOF marker

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Writing Packet Data

Helper methods for writing big-endian values into a byte[] buffer:

static void WriteByte(byte[] buffer, int offset, int value)
{
    buffer[offset] = (byte)(value & 0xFF);
}
 
static void WriteBool(byte[] buffer, int offset, bool value)
{
    buffer[offset] = (byte)(value ? 1 : 0);
}
 
static void WriteShort(byte[] buffer, int offset, short value)
{
    buffer[offset] = (byte)((value >> 8) & 0xFF);
    buffer[offset + 1] = (byte)(value & 0xFF);
}
 
static void WriteInt(byte[] buffer, int offset, int value)
{
    buffer[offset] = (byte)((value >> 24) & 0xFF);
    buffer[offset + 1] = (byte)((value >> 16) & 0xFF);
    buffer[offset + 2] = (byte)((value >> 8) & 0xFF);
    buffer[offset + 3] = (byte)(value & 0xFF);
}
 
static void WriteFloat(byte[] buffer, int offset, float value)
{
    byte[] bytes = BitConverter.GetBytes(value);
    if (BitConverter.IsLittleEndian)
        Array.Reverse(bytes);
    Buffer.BlockCopy(bytes, 0, buffer, offset, 4);
}
 
static void WriteLong(byte[] buffer, int offset, long value)
{
    buffer[offset] = (byte)((value >> 56) & 0xFF);
    buffer[offset + 1] = (byte)((value >> 48) & 0xFF);
    buffer[offset + 2] = (byte)((value >> 40) & 0xFF);
    buffer[offset + 3] = (byte)((value >> 32) & 0xFF);
    buffer[offset + 4] = (byte)((value >> 24) & 0xFF);
    buffer[offset + 5] = (byte)((value >> 16) & 0xFF);
    buffer[offset + 6] = (byte)((value >> 8) & 0xFF);
    buffer[offset + 7] = (byte)(value & 0xFF);
}
 
static void WriteEmptyItem(byte[] buffer, int offset)
{
    WriteShort(buffer, offset, (short)-1);
}
 
static void WriteItem(byte[] buffer, int offset, short id, byte count, short damage)
{
    WriteShort(buffer, offset, id);
    buffer[offset + 2] = count;
    WriteShort(buffer, offset + 3, damage);
}

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Precision Scaling

Some fields use fixed-point encoding integers on the wire representing floats/doubles with a multiplier applied:

Data Type	Multiplier	Wire Type	Description
Entity position	x 32	int	(int)(position * 32). 1/32 block precision.
Sound position	x 8	int	(int)(position * 8). 1/8 block precision.
Rotation	x 256 / 360	byte	(byte)(angle * 256.0 / 360.0).
Velocity	x 8000	short	(short)(velocity * 8000.0), clamped to +/-3.9 blocks/tick before encoding.

int wireX = (int)(player.getLocation().getX() * 32);
int wireY = (int)(player.getLocation().getY() * 32);
int wireZ = (int)(player.getLocation().getZ() * 32);
 
byte wireYaw = (byte)(player.getLocation().getYaw() * 256.0 / 360.0);
byte wirePitch = (byte)(player.getLocation().getPitch() * 256.0 / 360.0);

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Example: Playing a Sound Effect

Sends a LevelSoundPacket (ID 62) to play a ghast scream at the player's location whenever they chat.

[EventHandler]
public void onPlayerChat(PlayerChatEvent e)
{
    // LevelSoundPacket layout:
    //   [0]      byte   packet ID (62)
    //   [1..4]   int    sound type
    //   [5..8]   int    x * 8
    //   [9..12]  int    y * 8
    //   [13..16] int    z * 8
    //   [17..20] float  volume
    //   [21..24] float  pitch
    byte[] buffer = new byte[25];
    buffer[0] = (byte)62; // packet id
 
    WriteInt(buffer, 1, (int)19);  // eSoundType_MOB_GHAST_SCREAM (Sound.GHAST_SCREAM)
 
    WriteInt(buffer, 5,  (int)(e.getPlayer().getLocation().getX() * 8));
    WriteInt(buffer, 9,  (int)(e.getPlayer().getLocation().getY() * 8));
    WriteInt(buffer, 13, (int)(e.getPlayer().getLocation().getZ() * 8));
 
    WriteFloat(buffer, 17, 10);  // volume
    WriteFloat(buffer, 21, 1);   // pitch
 
    e.getPlayer().getConnection().send(buffer);
}

Sound type IDs correspond to the Sound enum. Cast any Sound value to int to get the wire value, for example (int)Sound.GHAST_SCREAM is 19.

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Example: Changing the Game Mode

GameEventPacket (ID 70) notifies the client of game state changes.

[EventHandler]
public void onJoin(PlayerJoinEvent e)
{
    // layout:
    //   [0]  byte  packet ID (70)
    //   [1]  byte  event type
    //   [2]  byte  parameter
    byte[] buffer = new byte[3];
    buffer[0] = (byte)70;  // packet id
    buffer[1] = (byte)3;   // CHANGE_GAME_MODE
    buffer[2] = (byte)1;   // 0 = Survival, 1 = Creative, 2 = Adventure
    e.getPlayer().getConnection().send(buffer);
}

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Example: Teleporting an Entity (Client-Side)

TeleportEntityPacket (ID 34) moves an entity to an absolute position on the client.

// Teleport entity 42 to (100.5, 64.0, -200.25)
byte[] buffer = new byte[17]
buffer[0] = (byte)34; // packet id
 
WriteShort(buffer, 1, (short)42); // entity id
WriteInt(buffer, 3,  (int)(100.5 * 32)); // x * 32
WriteInt(buffer, 7,  (int)(64.0 * 32)); // y * 32
WriteInt(buffer, 11, (int)(-200.25 * 32)); // z * 32
buffer[15] = (byte)(90.0 * 256.0 / 360.0); // yRot
buffer[16] = (byte)(0.0 * 256.0 / 360.0); // xRot
 
player.getConnection().send(buffer);

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Example: Setting the World Time

SetTimePacket (ID 4) updates the client's world time.

// set time to noon (6000 ticks)
byte[] buffer = new byte[17]
buffer[0] = (byte)4; // packet id
 
WriteLong(buffer, 1, 6000L); // game time (total ticks elapsed)
WriteLong(buffer, 9, 6000L); // day time (time of day, 0-24000)
 
player.getConnection().send(buffer);

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Example: Updating Health Display

SetHealthPacket (ID 8) updates the client's health, food, and saturation display.

// set health to 20 (full), food to 20 (full), saturation to 5.0
byte[] buffer = new byte[12];
buffer[0] = (byte)8; // packet id
 
WriteFloat(buffer, 1, 20.0f); // health
WriteShort(buffer, 5, (short)20); // food
WriteFloat(buffer, 7, 5.0f); // saturation
buffer[11] = (byte)0; // damage source (0 = unknown)
 
player.getConnection().send(buffer);

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Example: Setting Player Abilities

PlayerAbilitiesPacket (ID 202) updates the player's ability flags and speeds.

// enable flying for the player
byte[] buffer = new byte[10];
buffer[0] = (byte)202; // packet id
 
// 0x01=invulnerable, 0x02=flying, 0x04=canFly, 0x08=instabuild (creative)
buffer[1] = (byte)(0x02 | 0x04); // flying + canFly
 
WriteFloat(buffer, 2, 0.05f); // fly speed (default 0.05)
WriteFloat(buffer, 6, 0.1f); // walk speed (default 0.1)
 
player.getConnection().send(buffer);

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Example: Creating an Explosion Effect

ExplodePacket (ID 60) creates a client-side explosion with optional block destruction and knockback.

// create an explosion at (100.0, 64.0, 200.0) with radius 4.0 and no destroyed blocks
byte[] buffer = new byte[46];
buffer[0] = (byte)60; // packet id
 
buffer[1] = (byte)0; // knockbackOnly = false (full explosion with position data)
 
// position (double precision, 8 bytes each)
byte[] xBytes = BitConverter.GetBytes(100.0);
byte[] yBytes = BitConverter.GetBytes(64.0);
byte[] zBytes = BitConverter.GetBytes(200.0);
Buffer.BlockCopy(xBytes, 0, buffer, 2, 8);
Buffer.BlockCopy(yBytes, 0, buffer, 10, 8);
Buffer.BlockCopy(zBytes, 0, buffer, 18, 8);
 
WriteFloat(buffer, 26, 4.0f); // radius
WriteInt(buffer, 30, 0); // destroyed block count (0 = no blocks)
 
// knockback velocity applied to player
WriteFloat(buffer, 34, 0.0f); // knockback X
WriteFloat(buffer, 38, 0.5f); // knockback Y (push player up)
WriteFloat(buffer, 42, 0.0f); // knockback Z
 
player.getConnection().send(buffer);

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Example: Setting the XP Bar

SetExperiencePacket (ID 43) updates the XP bar.

// Set XP bar to 50% progress, level 10, total 300 XP
byte[] buffer = new byte[1 + 4 + 2 + 2]; // 9 bytes
buffer[0] = (byte)43; // packet id
 
WriteFloat(buffer, 1, 0.5f);        // bar progress (0.0 to 1.0)
WriteShort(buffer, 5, (short)10);   // level
WriteShort(buffer, 7, (short)300);  // total XP points
 
player.getConnection().send(buffer);

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Complete packet reference

All server-to-client packet layouts. The packet ID byte is always buffer[0] and is not listed in the field tables below. only the payload after the ID is shown.

General / Connection Packets

Packet 0 - KeepAlivePacket

Connection keepalive. The client echoes this back.

Offset	Type	Field	Description
0	int	id	Keepalive ID. The client should respond with the same value.

Total payload: 4 bytes.

Packet 3 - ChatPacket

Send a chat/system message to the client.

Offset	Type	Field	Description
0	short	messageType	Message type enum value.
2	short	packedCounts	Packed field: high nibble = string arg count, low nibble = int arg count. Computed as (stringCount << 4) \| intCount.
4	utf[]	stringArgs	Variable number of utf strings (the message text, source name, item name, etc).
...	int[]	intArgs	Variable number of int values (for example source entity type).

Total payload: variable. For a simple chat message, messageType = 0, one string arg (the message), zero int args. The packed counts would be (1 << 4) | 0 = 0x0010.

Packet 255 - DisconnectPacket

Disconnect the client.

Offset	Type	Field	Description
0	int	reason	Disconnect reason code.

Total payload: 4 bytes.

World & Environment Packets

Packet 4 - SetTimePacket

Set world time.

Offset	Type	Field	Description
0	long	gameTime	Total game time in ticks (monotonically increasing).
8	long	dayTime	Time of day in ticks (0-24000 range).

Total payload: 16 bytes.

Packet 6 - SetSpawnPositionPacket

Set the world spawn point.

Offset	Type	Field	Description
0	int	x	Spawn X coordinate.
4	int	y	Spawn Y coordinate.
8	int	z	Spawn Z coordinate.

Total payload: 12 bytes.

Packet 9 - RespawnPacket

Sent on respawn or dimension change.

Offset	Type	Field	Description
0	byte	dimension	Dimension ID (0=Overworld, -1=Nether, 1=End).
1	byte	gameType	Game mode ID (0=Survival, 1=Creative, 2=Adventure).
2	short	mapHeight	World height.
4	utf	levelType	Level type name (for example "DEFAULT", "FLAT").
...	long	mapSeed	World seed.
...	byte	difficulty	Difficulty (0=Peaceful, 1=Easy, 2=Normal, 3=Hard).
...	bool	newSeaLevel	Whether the new sea level is active.
...	short	newEntityId	The player's new entity ID.
...	short	xzSize	World XZ size.
...	byte	hellScale	Nether scale factor.

Total payload: variable (depends on level type string length).

Packet 53 - TileUpdatePacket

Update a single block.

Offset	Type	Field	Description
0	int	x	Block X coordinate.
4	byte	y	Block Y coordinate (0-255).
5	int	z	Block Z coordinate.
9	short	block	Block type ID.
11	byte	dataLevel	Block data/metadata value.

Total payload: 12 bytes.

Packet 54 - TileEventPacket

Trigger a block action (note blocks, pistons, chests).

Offset	Type	Field	Description
0	int	x	Block X coordinate.
4	short	y	Block Y coordinate.
6	int	z	Block Z coordinate.
10	byte	b0	Action parameter 1 (depends on block type).
11	byte	b1	Action parameter 2 (depends on block type).
12	short	tile	Block type ID.

Total payload: 14 bytes.

Packet 55 - TileDestructionPacket

Show a block breaking animation (crack overlay).

Offset	Type	Field	Description
0	int	id	Breaker entity ID.
4	int	x	Block X coordinate.
8	int	y	Block Y coordinate.
12	int	z	Block Z coordinate.
16	byte	state	Destroy stage (0-9). Any other value removes the overlay.

Total payload: 17 bytes.

Packet 60 - ExplodePacket

Explosion with optional block destruction and knockback.

Offset	Type	Field	Description
0	bool	knockbackOnly	If true, only knockback fields follow (no position/radius/blocks).

If knockbackOnly is false (typical explosion):

Offset	Type	Field	Description
1	double	x	Explosion center X.
9	double	y	Explosion center Y.
17	double	z	Explosion center Z.
25	float	radius	Explosion radius.
29	int	count	Number of destroyed block offsets.
33	byte[count*3]	offsets	For each block: 3 signed bytes (dx, dy, dz) relative to the center.
...	float	knockbackX	Player knockback velocity X.
...	float	knockbackY	Player knockback velocity Y.
...	float	knockbackZ	Player knockback velocity Z.

If knockbackOnly is true (just apply knockback, no visual explosion):

Offset	Type	Field	Description
1	float	knockbackX	Player knockback velocity X.
5	float	knockbackY	Player knockback velocity Y.
9	float	knockbackZ	Player knockback velocity Z.

Total payload: variable.

Packet 61 - LevelEventPacket

World event (sounds, particles, door effects, etc).

Offset	Type	Field	Description
0	int	type	Event type ID (for example 1000=click sound, 1005=bow sound, 2000=smoke, 2001=break block).
4	int	x	Block X coordinate.
8	byte	y	Block Y coordinate.
9	int	z	Block Z coordinate.
13	int	data	Event-specific data (for example block ID for break effect, direction for smoke).
17	bool	globalEvent	If true, event is global (all players hear it regardless of distance).

Total payload: 18 bytes.

Packet 62 - LevelSoundPacket

Play a sound at a position. Positions use x8 scaling.

Offset	Type	Field	Description
0	int	soundId	Sound type ID. Maps to the Sound enum.
4	int	x	X coordinate * 8.
8	int	y	Y coordinate * 8.
12	int	z	Z coordinate * 8.
16	float	volume	Sound volume (1.0 = normal).
20	float	pitch	Sound pitch (1.0 = normal).

Total payload: 24 bytes.

Packet 63 - LevelParticlesPacket

Spawn particles at a position.

Offset	Type	Field	Description
0	utf	name	Particle name string (for example "flame", "smoke", "heart").
...	float	x	Center X coordinate.
...	float	y	Center Y coordinate.
...	float	z	Center Z coordinate.
...	float	xDist	Random X offset range.
...	float	yDist	Random Y offset range.
...	float	zDist	Random Z offset range.
...	float	maxSpeed	Maximum particle speed.
...	int	count	Number of particles to spawn.

Total payload: variable (depends on particle name string length) + 32 bytes for the fixed fields.

Packet 70 - GameEventPacket

Game state change notification.

Offset	Type	Field	Description
0	byte	event	Event type.
1	byte	param	Event parameter.

Event types:

Value	Name	Parameter
0	No Bed	(unused)
1	Start Rain	(unused)
2	Stop Rain	(unused)
3	Change Game Mode	0=Survival, 1=Creative, 2=Adventure
4	Win Game	0=show credits, 1=just respawn

Total payload: 2 bytes.

Packet 130 - SignUpdatePacket

Update sign text.

Offset	Type	Field	Description
0	int	x	Sign X coordinate.
4	short	y	Sign Y coordinate.
6	int	z	Sign Z coordinate.
10	bool	verified	Whether the sign text has been verified.
11	bool	censored	Whether the sign text has been censored.
12	utf	line1	First line of text.
...	utf	line2	Second line of text.
...	utf	line3	Third line of text.
...	utf	line4	Fourth line of text.

Total payload: variable (12 bytes fixed + 4 * utf strings).

Entity Packets

Packet 8 - SetHealthPacket

Update health, food, and saturation.

Offset	Type	Field	Description
0	float	health	Current health (0.0-20.0, 20 = full).
4	short	food	Food level (0-20).
6	float	saturation	Food saturation level.
10	byte	damageSource	Damage source type (for telemetry).

Total payload: 11 bytes.

Packet 18 - AnimatePacket

Play an entity animation.

Offset	Type	Field	Description
0	int	entityId	Entity ID.
4	byte	action	Animation type (1=swing arm, 2=damage, 3=leave bed, 104=crouch, 105=uncrouch).

Total payload: 5 bytes.

Packet 20 - AddPlayerPacket

Spawn a named player entity.

Offset	Type	Field	Description
0	int	entityId	Entity ID.
4	utf	name	Player name.
...	int	x	X coordinate * 32 (fixed-point).
...	int	y	Y coordinate * 32 (fixed-point).
...	int	z	Z coordinate * 32 (fixed-point).
...	byte	yRot	Yaw (angle * 256 / 360).
...	byte	xRot	Pitch (angle * 256 / 360).
...	byte	yHeadRot	Head yaw (angle * 256 / 360).
...	short	carriedItem	Item ID of held item.
...	playerUID	xuid	Player XUID (8 bytes).
...	playerUID	onlineXuid	Online XUID for splitscreen guests (8 bytes).
...	byte	playerIndex	Local player index.
...	int	skinId	Custom skin ID.
...	int	capeId	Custom cape ID.
...	int	gamePrivileges	Player game privileges bitfield.
...	metadata	entityData	Entity metadata (SynchedEntityData).

Total payload: variable (includes entity metadata).

Packet 23 - AddEntityPacket

Spawn a non-mob entity (minecart, arrow, falling block, etc).

Offset	Type	Field	Description
0	short	entityId	Entity ID.
2	byte	type	Entity type ID (for example 1=boat, 10=minecart, 50=TNT, 60=arrow, 70=falling block).
3	int	x	X coordinate * 32 (fixed-point).
7	int	y	Y coordinate * 32 (fixed-point).
11	int	z	Z coordinate * 32 (fixed-point).
15	byte	yRot	Yaw (angle * 256 / 360).
16	byte	xRot	Pitch (angle * 256 / 360).
17	int	data	Entity-specific data (for example block ID for falling blocks, owner entity ID for projectiles).

If data is non-zero, three additional velocity fields follow:

Offset	Type	Field	Description
21	short	xVel	X velocity * 8000.
23	short	yVel	Y velocity * 8000.
25	short	zVel	Z velocity * 8000.

Total payload: 21 bytes (no velocity) or 27 bytes (with velocity).

Packet 24 - AddMobPacket

Spawn a mob.

Offset	Type	Field	Description
0	short	entityId	Entity ID.
2	byte	mobType	Mob type ID (for example 50=Creeper, 51=Skeleton, 52=Spider, 54=Zombie, 90=Pig, 91=Sheep).
3	int	x	X coordinate * 32 (fixed-point).
7	int	y	Y coordinate * 32 (fixed-point).
11	int	z	Z coordinate * 32 (fixed-point).
15	byte	yRot	Yaw (angle * 256 / 360).
16	byte	xRot	Pitch (angle * 256 / 360).
17	byte	yHeadRot	Head yaw (angle * 256 / 360).
18	short	xVel	X velocity * 8000.
20	short	yVel	Y velocity * 8000.
22	short	zVel	Z velocity * 8000.
24	metadata	entityData	Entity metadata (SynchedEntityData).

Total payload: 24 bytes + variable metadata.

Packet 26 - AddExperienceOrbPacket

Spawn an XP orb.

Offset	Type	Field	Description
0	int	entityId	Entity ID.
4	int	x	X coordinate * 32 (fixed-point).
8	int	y	Y coordinate * 32 (fixed-point).
12	int	z	Z coordinate * 32 (fixed-point).
16	short	value	XP value of the orb.

Total payload: 18 bytes.

Packet 28 - SetEntityMotionPacket

Set entity velocity. Has two encoding modes based on a flag bit in the entity ID field.

The first field is a short combining the entity ID and a flag:

• Bits 0-10 (mask 0x07FF): Entity ID (max 2047).
• Bit 11 (mask 0x0800): If set, velocity uses 3 bytes (lower precision). If clear, 3 shorts (full precision).

Full precision mode (flag clear):

Offset	Type	Field	Description
0	short	idAndFlag	Entity ID (low 11 bits), flag=0.
2	short	xVel	X velocity * 8000.
4	short	yVel	Y velocity * 8000.
6	short	zVel	Z velocity * 8000.

Total payload: 8 bytes.

Compact mode (flag set, bit 11 = 1):

Offset	Type	Field	Description
0	short	idAndFlag	Entity ID (low 11 bits) OR 0x0800.
2	byte	xVel	X velocity / 16 (sign-extended, then multiplied by 16 on read).
3	byte	yVel	Y velocity / 16.
4	byte	zVel	Z velocity / 16.

Total payload: 5 bytes. The server automatically picks compact mode when velocity values fit.

Packet 29 - RemoveEntitiesPacket

Despawn one or more entities.

Offset	Type	Field	Description
0	byte	count	Number of entities to remove.
1	int[count]	entityIds	Array of entity IDs (4 bytes each).

Total payload: 1 + (count * 4) bytes.

Packets 30-33 - MoveEntityPacket

Relative entity movement/rotation updates. Four sub-types:

Packet 30 - MoveEntityPacket (base, no movement): short entityId only. Payload: 2 bytes.

Packet 31 - MoveEntityPacket.Pos (position only):

Offset	Type	Field	Description
0	short	entityId	Entity ID.
2	byte	dx	X delta (signed, in 1/32 block units).
3	byte	dy	Y delta.
4	byte	dz	Z delta.

Payload: 5 bytes.

Packet 32 - MoveEntityPacket.Rot (rotation only):

Offset	Type	Field	Description
0	short	entityId	Entity ID.
2	byte	yRot	New yaw (angle * 256 / 360).
3	byte	xRot	New pitch (angle * 256 / 360).

Payload: 4 bytes.

Packet 33 - MoveEntityPacket.PosRot (position + rotation):

Offset	Type	Field	Description
0	short	entityId	Entity ID.
2	byte	dx	X delta.
3	byte	dy	Y delta.
4	byte	dz	Z delta.
5	byte	yRot	New yaw.
6	byte	xRot	New pitch.

Payload: 7 bytes.

Packet 34 - TeleportEntityPacket

Teleport an entity to an absolute position.

Offset	Type	Field	Description
0	short	entityId	Entity ID.
2	int	x	X coordinate * 32 (fixed-point).
6	int	y	Y coordinate * 32 (fixed-point).
10	int	z	Z coordinate * 32 (fixed-point).
14	byte	yRot	Yaw (angle * 256 / 360).
15	byte	xRot	Pitch (angle * 256 / 360).

Total payload: 16 bytes.

Packet 35 - RotateHeadPacket

Update an entity's head rotation.

Offset	Type	Field	Description
0	int	entityId	Entity ID.
4	byte	yHeadRot	Head yaw (angle * 256 / 360).

Total payload: 5 bytes.

Packet 38 - EntityEventPacket

Trigger an entity event (hurt, death, eating, etc).

Offset	Type	Field	Description
0	int	entityId	Entity ID.
4	byte	eventId	Event type (2=hurt, 3=death, 9=eating finished).

Total payload: 5 bytes.

Packet 39 - SetEntityLinkPacket

Attach or detach entities (leash, riding).

Offset	Type	Field	Description
0	int	sourceId	Entity being attached (the rider/leashed entity).
4	int	destId	Entity being attached to (the vehicle/fence). -1 to detach.
8	byte	type	Link type.

Total payload: 9 bytes.

Packet 40 - SetEntityDataPacket

Update entity metadata. See Metadata Encoding for how to construct the metadata blob.

Offset	Type	Field	Description
0	int	entityId	Entity ID.
4	metadata	data	Packed entity metadata entries.

Total payload: 4 bytes + variable metadata.

Packet 41 - UpdateMobEffectPacket

Apply or update a potion effect.

Offset	Type	Field	Description
0	int	entityId	Entity ID.
4	byte	effectId	Effect ID (1=speed, 2=slowness, 3=haste, 4=mining fatigue, 5=strength, ...).
5	byte	amplifier	Effect level (0 = level I, 1 = level II, etc).
6	short	duration	Duration in ticks.

Total payload: 8 bytes.

Packet 42 - RemoveMobEffectPacket

Remove a potion effect.

Offset	Type	Field	Description
0	int	entityId	Entity ID.
4	byte	effectId	Effect ID to remove.

Total payload: 5 bytes.

Packet 43 - SetExperiencePacket

Update the XP bar.

Offset	Type	Field	Description
0	float	progress	XP bar fill amount (0.0-1.0).
4	short	level	Current level.
6	short	totalXP	Total experience points.

Total payload: 8 bytes.

Packet 71 - AddGlobalEntityPacket

Spawn a global entity (lightning bolt).

Offset	Type	Field	Description
0	int	entityId	Entity ID.
4	byte	type	Entity type (1 = lightning bolt).
5	int	x	X coordinate * 32 (fixed-point).
9	int	y	Y coordinate * 32 (fixed-point).
13	int	z	Z coordinate * 32 (fixed-point).

Total payload: 17 bytes.

Player Packets

Packet 5 - SetEquippedItemPacket

Change the visible held item for an entity.

Offset	Type	Field	Description
0	int	entityId	Entity ID.
4	short	slot	Equipment slot (0=held).
6	item	item	Item data (see Item Data).

Total payload: 6 bytes + item data (2 bytes if empty, 5 bytes if present).

Packet 200 - AwardStatPacket

Award a statistic or achievement.

Offset	Type	Field	Description
0	int	statId	Statistic/achievement ID.
4	int	length	Length of parameter data blob in bytes.
8	byte[length]	data	Parameter data (typically a 4-byte int count).

Total payload: 8 bytes + length bytes. For a simple stat increment, length = 4 and data contains an int count.

Packet 202 - PlayerAbilitiesPacket

Update player abilities.

Offset	Type	Field	Description
0	byte	flags	Bitfield: 0x01=invulnerable, 0x02=flying, 0x04=canFly, 0x08=instabuild (creative).
1	float	flySpeed	Fly speed (default 0.05).
5	float	walkSpeed	Walk speed (default 0.1).

Total payload: 9 bytes.

Container Packets

Packet 100 - ContainerOpenPacket

Open a container window.

Offset	Type	Field	Description
0	byte	containerId	Window ID.
1	byte	type	Container type (0=chest, 1=workbench, 2=furnace, 3=dispenser, 4=enchanting table).
2	byte	size	Number of slots.
3	bool	customName	Whether a custom title follows.

If type == HORSE (type 12):

Offset	Type	Field	Description
4	int	entityId	Horse entity ID.

If customName is true:

Offset	Type	Field	Description
...	utf	title	Custom container title.

Total payload: 4 bytes minimum, variable with conditionals.

Packet 101 - ContainerClosePacket

Close a container window.

Offset	Type	Field	Description
0	byte	containerId	Window ID.

Total payload: 1 byte.

Packet 103 - ContainerSetSlotPacket

Set a single slot in a container.

Offset	Type	Field	Description
0	byte	containerId	Window ID.
1	short	slot	Slot index.
3	item	item	Item data (see Item Data).

Total payload: 3 bytes + item data (2 bytes if empty, 5 bytes if present).

Packet 104 - ContainerSetContentPacket

Set all slots in a container.

Offset	Type	Field	Description
0	byte	containerId	Window ID.
1	short	count	Number of item slots.
3	item[count]	items	Array of item data entries.

Total payload: 3 bytes + count * item data.

All Packet IDs

Every registered packet. S-C = server to client, C-S = client to server.

Just know that some of these packets have no function (such as scoreboards), most should work.

ID	Name	S-C	C-S	Notes
0	KeepAlivePacket	✓	✓	Connection keepalive.
1	LoginPacket	✓	✓	Login handshake.
2	PreLoginPacket	✓	✓	Pre-login handshake.
3	ChatPacket	✓	✓	Chat messages.
4	SetTimePacket	✓		World time.
5	SetEquippedItemPacket	✓		Held item display.
6	SetSpawnPositionPacket	✓		World spawn point.
7	InteractPacket		✓	Player interact with entity.
8	SetHealthPacket	✓		Health/food/saturation.
9	RespawnPacket	✓	✓	Respawn/dimension change.
10	MovePlayerPacket	✓	✓	Player position (base).
11	MovePlayerPacket.Pos	✓	✓	Player position only.
12	MovePlayerPacket.Rot	✓	✓	Player rotation only.
13	MovePlayerPacket.PosRot	✓	✓	Player position + rotation.
14	PlayerActionPacket		✓	Block breaking, item dropping.
15	UseItemPacket		✓	Place block / use item.
16	SetCarriedItemPacket	✓	✓	Hotbar slot selection.
17	EntityActionAtPositionPacket	✓		Sleep in bed.
18	AnimatePacket	✓	✓	Entity animations.
19	PlayerCommandPacket		✓	Sneak, sprint, etc.
20	AddPlayerPacket	✓		Spawn named player.
22	TakeItemEntityPacket	✓		Item pickup animation.
23	AddEntityPacket	✓		Spawn non-mob entity.
24	AddMobPacket	✓		Spawn mob.
25	AddPaintingPacket	✓		Spawn painting.
26	AddExperienceOrbPacket	✓		Spawn XP orb.
27	PlayerInputPacket		✓	Vehicle steering input.
28	SetEntityMotionPacket	✓		Entity velocity.
29	RemoveEntitiesPacket	✓		Despawn entities.
30	MoveEntityPacket	✓		Entity movement (base).
31	MoveEntityPacket.Pos	✓		Entity position delta.
32	MoveEntityPacket.Rot	✓		Entity rotation.
33	MoveEntityPacket.PosRot	✓		Entity pos + rot delta.
34	TeleportEntityPacket	✓		Entity absolute position.
35	RotateHeadPacket	✓		Entity head rotation.
38	EntityEventPacket	✓		Entity events (hurt, death).
39	SetEntityLinkPacket	✓		Leash / riding.
40	SetEntityDataPacket	✓		Entity metadata update.
41	UpdateMobEffectPacket	✓		Apply potion effect.
42	RemoveMobEffectPacket	✓		Remove potion effect.
43	SetExperiencePacket	✓		XP bar update.
44	UpdateAttributesPacket	✓		Entity attributes.
50	ChunkVisibilityPacket	✓		Chunk visibility.
51	BlockRegionUpdatePacket	✓		Chunk data.
52	ChunkTilesUpdatePacket	✓		Multi-block change.
53	TileUpdatePacket	✓		Single block change.
54	TileEventPacket	✓		Block action.
55	TileDestructionPacket	✓		Block breaking animation.
60	ExplodePacket	✓		Explosion.
61	LevelEventPacket	✓		World event (sounds, particles).
62	LevelSoundPacket	✓		Sound effect.
63	LevelParticlesPacket	✓		Particle effect.
70	GameEventPacket	✓		Game state change.
71	AddGlobalEntityPacket	✓		Lightning bolt.
100	ContainerOpenPacket	✓		Open container.
101	ContainerClosePacket	✓	✓	Close container.
102	ContainerClickPacket		✓	Click container slot.
103	ContainerSetSlotPacket	✓	✓	Set container slot.
104	ContainerSetContentPacket	✓		Set all container slots.
105	ContainerSetDataPacket	✓		Container progress bar data.
106	ContainerAckPacket	✓	✓	Transaction acknowledgement.
107	SetCreativeModeSlotPacket	✓	✓	Creative inventory action.
108	ContainerButtonClickPacket		✓	Enchanting / other button.
130	SignUpdatePacket	✓	✓	Sign text update.
131	ComplexItemDataPacket	✓		Map data.
132	TileEntityDataPacket	✓		Tile entity NBT data.
133	TileEditorOpenPacket	✓		Open tile entity editor.
200	AwardStatPacket	✓		Award statistic.
201	PlayerInfoPacket	✓	✓	Player list info.
202	PlayerAbilitiesPacket	✓	✓	Player abilities.
206	SetObjectivePacket	✓		Scoreboard objective.
207	SetScorePacket	✓		Scoreboard score.
208	SetDisplayObjectivePacket	✓		Scoreboard display slot.
209	SetPlayerTeamPacket	✓		Scoreboard team.
255	DisconnectPacket	✓	✓	Disconnect.

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Where to Look

• PlayerConnection - Get it via player.getConnection(). This is what you call send() on.
• Sound - All sound type IDs for LevelSoundPacket (62). Cast to int for the wire value.
• GameMode - Game mode constants for GameEventPacket (70) and PlayerAbilitiesPacket (202).
• Location - Get world coordinates from player.getLocation() for position encoding.
• Packet source files - The definitive reference is the write() method of each packet class in thre code (for example LevelSoundPacket.cpp, TeleportEntityPacket.cpp).

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Extra info

• Packet IDs are a single byte. Only the low byte matters on the wire.
• Position values in entity packets use *32 fixed-point. Sound event positions use *8.
• Rotation angles are a single byte: (byte)(angle * 256.0 / 360.0).
• Velocity is (short)(velocity * 8000.0), clamped to +/-3.9 blocks/tick before encoding.
• Strings use modified UTF-8 with a 2-byte length prefix.
• Item data writes -1 as a short for empty slots (2 bytes), or short ID + byte count + short damage for occupied slots (5 bytes).
• The 4-byte size header is written by the server automatically - don't include it in your byte array.
• FourKit's Sound enum values map directly to the sound IDs used in LevelSoundPacket. VERY USEFUL!!!!
• If you send malformed data, the client will likely disconnect or crash, or do some funny weird stuff. Test carefully.
• Some packets have conditional fields (ExplodePacket, ContainerOpenPacket, SetEntityMotionPacket). Read the wire format tables above carefully.
• Entity metadata - see Metadata Encoding for how to construct SynchedEntityData blobs by hand.