message

A message is delivered from several sources:

• They are sent via the Real Time Messaging API when a message is sent to a channel to which you subscribe. This message should immediately be displayed in the client.
• They are returned via calls to conversations.history

A basic message:

{
	"type": "message",
	"channel": "C123ABC456",
	"user": "U123ABC456",
	"text": "Hello world",
	"ts": "1355517523.000005"
}

The channel property is the ID of the channel, private group or DM channel this message is posted in. The user property is the ID of the user speaking, the text property is the text spoken, and ts is the unique (per-channel) timestamp.

Messages can also include an attachments property, containing a list of attachment objects.

If the message has been edited after posting it will include an edited property, including the user ID of the editor, and the timestamp the edit happened. The original text of the message is not available. For example:

{
	"type": "message",
	"channel": "C123ABC456",
	"user": "U123ABC456",
	"text": "Hello, world!",
	"ts": "1355517523.000005",
	"edited": {
		"user": "U123ABC456",
		"ts": "1355517536.000001"
	}
}

Message subtypes

Unlike other event types, message events can have a subtype. For example, this is a channel join message:

{
	"type": "message",
	"subtype": "channel_join",
	"text": "<@U123ABC456|bobby> has joined the channel",
	"ts": "1403051575.000407",
	"user": "U123ABC456"
}

They are structured in this way so that clients can either support them fully by having distinct behavior for each different subtype, or can fallback to just displaying the text of the message.

The full list of message subtypes is:

Hidden subtypes

Some subtypes have a special hidden property. These indicate messages that are part of the history of a channel but should not be displayed to users. Examples include records of message edits or deletes:

{
	"type": "message",
	"subtype": "message_deleted",
	"hidden": true,
	"channel": "C123ABC456",
	"ts": "1358878755.000001",
	"deleted_ts": "1358878749.000002",
	"event_ts": "1358878755.000002"
}

Hidden messages will not appear as the latest property on channel, group or im objects. They will also not return in calls to conversations.history.

Stars, pins, and reactions

Messages can have several extra properties depending on whether or not they have been starred, pinned, or reacted to:

{
	"type": "message",
	"channel": "C123ABC456",
	"user": "U123ABC456",
	"text": "Hello world",
	"ts": "1355517523.000005",
	"is_starred": true,
	"pinned_to": ["C024BE7LT", ...],
	"reactions": [
		{
			"name": "astonished",
			"count": 3,
			"users": [ "U1", "U2", "U3" ]
		},
		{
			"name": "facepalm",
			"count": 1034,
			"users": [ "U1", "U2", "U3", "U4", "U5" ]
		}
	]
}

The is_starred property is present and true if the calling user has starred the message, else it is omitted.

The pinned_to array, if present, contains the IDs of any channels to which the message is currently pinned.

The reactions property, if present, contains any reactions that have been added to the message and gives information about the type of reaction, the total number of users who added that reaction and a (possibly incomplete) list of users who have added that reaction to the message. The users array in the reactions property might not always contain all users that have reacted (we limit it to X users, and X might change), however count will always represent the count of all users who made that reaction (i.e. it may be greater than users.length). If the authenticated user has a given reaction then they are guaranteed to appear in the users array, regardless of whether count is greater than users.length or not.

Message events in the Events API

This exact event type is defined differently in the Events API. Depending on your associated OAuth scope or the channels your bot user belongs to, you must subscribe to one of the following events instead:

• message.channels - for messages appearing within channels
• message.im - for messages appearing within direct messages
• message.groups - for messages appearing within private channels
• message.mpim - for messages appearing within multiparty direct messages

The semantics for the events are the same as those described here — you're still receiving an event of type message.

Not all message subtypes are deliverable in the Events API.