Plugin channels

Plugin channels allow client mods and server plugins to communicate without cluttering up chat. This post by Dinnerbone is a good introduction and basic documentation.

Definitions

Data Types

PathEntity

Represents calculated path of entity.

Name	Type	Notes
Current path index	Int	Index in the points array that the entity is currently targeting.
Target	PathPoint
Number of points	Int	Number of elements in the following array
Points array	Array of PathPoint	The actual points on the path
Open set length	Int	Number of elements in the following array
Open set	Array of PathPoint
Closed set length	Int	Number of elements in the following array
Closed set	Array of PathPoint

You can read more here[1].

PathPoint

Represents single point in path

Name	Type	Notes
X	Int
Y	Int
Z	Int
Distance from origin	Float
Cost	Float
Cost malus	Float	Number that is rendered
Has been visited	Boolean
Node type	Int Enum	See below
Distance to target	Float

Values for node type:

• 0: BLOCKED
• 1: OPEN
• 2: WALKABLE
• 3: TRAPDOOR
• 4: FENCE
• 5: LAVA
• 6: WATER
• 7: WATER_BORDER
• 8: RAIL
• 9: DANGER_FIRE
• 10: DAMAGE_FIRE
• 11: DANGER_CACTUS
• 12: DAMAGE_CACTUS
• 13: DANGER_OTHER
• 14: DAMAGE_OTHER
• 15: DOOR_OPEN
• 16: DOOR_WOOD_CLOSED
• 17: DOOR_IRON_CLOSED
• 18: BREACH
• 19: LEAVES
• 20: STICKY_HONEY
• 21: COCOA

Reserved channels

minecraft:register

Two-way

Allows the client or server to register for one or more custom channels, indicating that data should be sent on those channels if the receiving end supports it too. Payload is a null (0x00) separated list of strings.

This channel was renamed from REGISTER in 1.13.

minecraft:unregister

Two-way

Allows the client or server to unregister from one or more custom channels, indicating that the receiving end should stop sending data on those channels. Payload is a null-separated list of strings. This is only useful if plugins are disabled/unloaded while the client is connected.

This channel was renamed from UNREGISTER in 1.13.

Channels internal to Minecraft

Since 1.3, Minecraft itself uses several plugin channels to implement new features. These internal channels use the minecraft namespace. They are not formally registered using the register channel. The vanilla Minecraft server will send these packets regardless, and the vanilla client will accept them.

Note that there were originally more channels included, but most of these were removed in 1.13. See this revision of the article for the original list. As of 1.14, the only remaining channels other than the brand one are debugging-related channels, which are not normally sent.

minecraft:brand

Two-way

For version 1.12.2(protocol version 340) and below, channel name is: MC|Brand

Announces the server and client implementation name right after a player has logged in. For the Notchian client and server, this is "vanilla" (which is chosen using the function net.minecraft.client.ClientBrandRetriever.getClientModName() and encoded as a UTF-8 string).

These brands are used in crash reports and a few other locations. It's recommended that custom clients and servers use their own brand names for the purpose of identification (for the Notchian client, the class used to get the brand is one of the few non-obfuscated classes). The brand is not processed in any other way, and Notchian clients will connect to servers with different brands with no issue (the brand is not used to validate).

The Notchian server sends a minecraft:brand packet right after it sends a Login (play) packet, and the Notchian client sends it right after receiving a Login (play) packet. However, some modified clients and servers will not send this packet (or will take longer to send it than normal), so it is important to not crash if the brand has not been sent. Additionally, the brand may change at any time (for instance, if connected through a BungeeCord instance, you may switch from a server with one brand to a server with another brand without receiving a Login (play) packet).

minecraft:debug/path

Server to client

What appears to be the purpose of minecraft:debug/path as seen in the snapshot 16w14a announcement. This is not found in the normal game.

Never sent, but does something with pathfinding debugging. The client reads the data and stores it, but its renderer cannot be enabled without modifications.

Name	Type	Notes
Unknown 1	Int	Used as a key in the mapping that stores this data; might be an entity ID?
Unknown 2	Float	Appears to be the "radius" of the squares for each pathpoint
Entity	PathEntity	See Data Types above

PathEntity's index point is rendered red; the others are rendered blue. PathEntity's target PathPoint is rendered as a green cube. PathPoint's closed set is rendered red, and open set is rendered green.

minecraft:debug/neighbors_update

Server to client

Never sent, but used to debug block updates. Does not render without modifying the client.

Name	Type	Notes
Time	VarLong	World timestamp at which the update occurred. 200 ticks after this timestamp, the given update stops rendering.
Location	Position	Location of the block that updated.

minecraft:debug/structures

Server to client

Never sent, but (presumably) used to debug structures. Does not render without modifying the client.

Adds a single new structure, which will always be rendered if the player is in the same dimension.

Field name		Field type		Notes
Dimension		Int		The dimension the structure is in.
Bounding box minX		Int		Main box for the structure (rendered in white). min must be less than max
Bounding box minY		Int
Bounding box minZ		Int
Bounding box maxX		Int
Bounding box maxY		Int
Bounding box maxZ		Int
Count		Int		Number of elements in the following array
Sub-boxes	Bounding box minX	Array	Int	min must be less than max
	Bounding box minY		Int
	Bounding box minZ		Int
	Bounding box maxX		Int
	Bounding box maxY		Int
	Bounding box maxZ		Int
	Flag		Boolean	If true, the sub-box is rendered in green, otherwise in blue.

minecraft:debug/worldgen_attempt

Server to client

Never sent, but (presumably) used to debug something with world generation. Does not render without modifying the client.

Adds a colored cube of the list of things to render. This cube is never removed.

Field name	Field type	Notes
Location	Position	The center of the location to render.
Size	Float	Diameter/side length of a cube to render.
Red	Float	Red value to render, from 0.0 to 1.0.
Green	Float	Green value to render, from 0.0 to 1.0.
Blue	Float	Blue value to render, from 0.0 to 1.0.
Alpha	Float	Alpha value to render, from 0.0 to 1.0.

minecraft:debug/poi_ticket_count

Server to client

Never sent, but used to set amount of free tickets for POI

Field name	Field type
Location of POI	Position
Num of tickets	VarInt

minecraft:debug/poi_added

Server to client

Never sent, but used to add debugging POI. Does not render without modifying the client.

Field name	Field type	Notes
Location	Positon	Location of POI
POI Type	String (x)	Type of POI, see the POI article
Tickets	VarInt	Amount of free tickets

minecraft:debug/poi_removed

Server to client

Never sent, but used to remove debugging POI. Does not render without modifying the client.

Field name	Field type	Notes
Location	Positon	Location of POI

minecraft:debug/village_sections

Server to client

Never sent, but used to add/remove debugging VilliageSections. Does not render without modifying the client.

Field name	Field type	Notes
Num of VillageSection locations to be added	VarInt	Number of VillageSection locations in following fields.
Location of VillageSection	Array of Position	Locations of VillageSections
Num of VillageSection locations to be removed	VarInt	Number of VillageSection locations in following fields.
Location of VillageSection	Array of Position	Locations of VillageSections

minecraft:debug/goal_selector

Server to client

Never sent, but (presumably) used to debug goal selectors. Does not render without modifying the client.

Adds multiple lines of text on the given location, spaced by 0.25 units upward on the Y-axis.

Field name		Field type		Notes
Location		Position		The location of the goal selector.
Unknown		Int		Key for the goal selector mapping, possibly entity ID.
Count		Int		Number of elements in the following array.
Goals	Priority	Array	Int	Currently unused
	Is running		Boolean	Defines the color of the text. #00FF00 if true, #CCCCCC otherwise
	Name		String (255)

minecraft:debug/brain

Server to client

Never sent. Used to debug villager's brain. Doesn't render without modifying the client.

Field name	Field type	Notes
X	Double	X coordinate of villager's position
Y	Double	Y coordinate of villager's position
Z	Double	Z coordinate of villager's position
Unique ID	UUID	Villager's Unique ID
Entity ID	EID	Villager's Entity ID
Name	String (x)	Villager's name
Profession	String (x)	Villager's profession
XP	VarInt	Villager's experience points
Inventory	String (x)	Villager's inventory (need more research on that)
Has path	Boolean	Indicates whether the next field is Path
Path	PathEntity	Movement path
Wants golem	Boolean	Indicates whether the villager in need of Golem.

minecraft:debug/bee

Server to client

Never sent, but (presumably) used to debug bee pathfinding to hives and flowers. Does not render without modifying the client.

Field name	Field type	Notes
X	Double	X coordinate of rendering location
Y	Double	Y coordinate of rendering location
Z	Double	Z coordinate of rendering location
Unique ID	UUID	Bee's unique ID
EID	VarInt	EID of the Bee
Has hive position	Boolean	True if following field value is location of bee hive.
Location of hive	Position	Optional position of bee hive.
Has flower position	Boolean	True if following field value is location of flower.
Location of flower	Position	Optional position of flower.
Travel ticks	VarInt	Purpose unknown.
Has path	Boolean	True if following field value is path.
Path	PathEntity	Serialized path.
Num of goals	VarInt	Number of goals in following fields.
Goal	Array of String (x)	Probably string name of goal
Num of blacklisted hives	VarInt	Number of blacklisted hives in following fields.
Blacklisted hive	Array of Position	Position of blacklisted hive.

minecraft:debug/hive

Server to client

Never sent, but (presumably) used to debug hives. Does not render without modifying the client.

Field name	Field type	Notes
Location	Position	Rendering location. If a player is more than 30 blocks away, rendering is skipped.
Hive type	String	Name of hive type
Occupant count	VarInt	Number of bees inside this hive
Honey level	VarInt	Level of honey inside this hive
Sedated	Boolean	True if bees are sedated, false otherwise
Last seen	VarLong	Never used in debug renderer?

minecraft:debug/game_test_add_marker

Server to client

Never sent, but used to set different debug markers in the world. Does not render for vanilla clients below version 1.16.5.

Field name	Field type	Notes
Location	Position	Location of the marker.
Color	VarInt	Encoded ARGB color (Read below about encoding).
Name	String (x)	Name of marker
Lifetime	VarInt	Time in milliseconds, after which the marker will be destroyed

Color can be encoded as following:

int encoded = 0;
encoded = encoded | ((int) blueChannel);
encoded = encoded | ((int) greenChannel << 8);
encoded = encoded | ((int) redChannel << 16);
encoded = encoded | ((int) alphaChannel << 24);
return encoded;

Note that color is normalized by client.

minecraft:debug/game_test_clear

Clears all debug markers.

minecraft:debug/raids

Server to client

Never sent, but used to set debug raid centers. Does not render without modifying the client.

Field name	Field type	Notes
Num of locations	VarInt	Number of locations provided by following array
Locations	Array of Position	Locations of raid centers

minecraft:debug/game_event

Server to client

Never sent, but used to debug game events. Does not render without modifying the client.

Field name	Field type	Notes
Game event identifier	String (x)
Game event location	Position

minecraft:debug/game_event_listeners

Server to client

Never sent, but used to track game event listeners. Does not render without modifying the client.

Field name	Field type	Notes
Position source type	Identifier
Listener data	Byte Array
Listener range	VarInt

Position source type	Identifier	Data
Block position source	minecraft:block	Data contain single block position
Entity position source	minecraft:entity	Data contain single EID

MC|PingHost

Client to server

Sent after a Server list ping in Minecraft 1.6. More information on Server List Ping#1.6. In 1.7 and above, the Request (Status, 0x00, serverbound) packet is instead sent before the ping.

Since this plugin channel is only sent for the legacy server list ping, it uses the older packet structure.

Notable community plugin channels

Channels listed in this section are not used by the vanilla Minecraft client or server. This is just a likely-incomplete list of channels used by mods/plugins popular within the Minecraft community.

bungeecord:main

Formerly BungeeCord; additionally, note that the channel name is remapped by spigot so that the old name can still be used in plugins.

See here

fml:handshake, fml:play

Main article: Minecraft Forge Handshake

Previously FML|HS, FML

Used by Minecraft Forge to negotiate required mods, among other things. fml:handshake and fml:play

ML|OpenTE

Server to client

Used by ModLoader to support custom GUI windows. Does not use the REGISTER channel.

WECUI

Main article: /WorldEditCUI

Used by the server-side WorldEdit and the client-side WorldEditCUI to coordinate selections.

wdl:init, wdl:control, wdl:request

Main article: /World downloader

Used by the client-side World Downloader mod to get permission information and perform permission requests.

world_info, world_id, worldinfo:world_id

Used by VoxelMap and JourneyMap (1.16.5+) to query the world ID, which is useful on BungeeCord-style server networks to keep maps unique.