You must enable javascript in order to use Slack. You can do this in your browser settings.

chat.postMessage

Sends a message to a channel.

Facts

Method URL:https://slack.com/api/chat.postMessage
Preferred HTTP method:POST
Accepted content types:application/x-www-form-urlencoded, application/json
Rate limiting:Special
Works with:
Token typeRequired scope(s)
botchat:write 
userchat:write  chat:write:user  chat:write:bot 
classic botbot

This method posts a message to a public channel, private channel, or direct message/IM channel.

Arguments

token

Authentication token bearing required scopes.

Examplexxxx-xxxxxxxxx-xxxx
channel

Channel, private group, or IM channel to send message to. Can be an encoded ID, or a name. See below for more details.

ExampleC1234567890
text

How this field works and whether it is required depends on other fields you use in your API call. See below for more detail.

ExampleHello world
as_user

Pass true to post the message as the authed user, instead of as a bot. Defaults to false. See authorship below. This argument may not be used with newer bot tokens.

Exampletrue
attachments

A JSON-based array of structured attachments, presented as a URL-encoded string.

Example[{"pretext": "pre-hello", "text": "text-world"}]
blocks

A JSON-based array of structured blocks, presented as a URL-encoded string.

Example[{"type": "section", "text": {"type": "plain_text", "text": "Hello world"}}]
icon_emoji

Emoji to use as the icon for this message. Overrides icon_url. Must be used in conjunction with as_user set to false, otherwise ignored. See authorship below. This argument may not be used with newer bot tokens.

Example:chart_with_upwards_trend:
icon_url

URL to an image to use as the icon for this message. Must be used in conjunction with as_user set to false, otherwise ignored. See authorship below. This argument may not be used with newer bot tokens.

Examplehttp://lorempixel.com/48/48
link_names

Find and link channel names and usernames.

Exampletrue
mrkdwn

Disable Slack markup parsing by setting to false. Enabled by default.

Default: true

Examplefalse
parse

Change how messages are treated. Defaults to none. See below.

Examplefull
reply_broadcast

Used in conjunction with thread_ts and indicates whether reply should be made visible to everyone in the channel or conversation. Defaults to false.

Exampletrue
thread_ts

Provide another message's ts value to make this message a reply. Avoid using a reply's ts value; use its parent instead.

Example1234567890.123456
unfurl_links

Pass true to enable unfurling of primarily text-based content.

Exampletrue
unfurl_media

Pass false to disable unfurling of media content.

Examplefalse
username

Set your bot's user name. Must be used in conjunction with as_user set to false, otherwise ignored. See authorship below.

ExampleMy Bot

This method supports application/json via HTTP POST. Present your token in your request's Authorization header. Learn more.

Please note that the as_user parameter may not be used by new Slack apps. Read more about Authorship to understand how as_user works for classic Slack apps.

Using text with blocks or attachments

The usage of the text field changes depending on whether you're using blocks. If you are using blocks, this is used as a fallback string to display in notifications. If you aren't, this is the main body text of the message. It can be formatted as plain text, or with mrkdwn.

The text field is not enforced as required when using blocks or attachments. However, we highly recommended that you include text to provide a fallback when using blocks, as described above.

JSON POST support

As of October 2017, it's now possible to send a well-formatted application/json POST body to chat.postMessage and other Web API write methods. No need to carefully URL-encode your JSON attachments and present all other fields as URL encoded key/value pairs; just send JSON instead.

Now you can send messages lovingly authored with the message builder to chat.postMessage without further modification.

Learn more about this support in the Web API docs or this changelog.

Response

Typical success response

{
    "ok": true,
    "channel": "C1H9RESGL",
    "ts": "1503435956.000247",
    "message": {
        "text": "Here's a message for you",
        "username": "ecto1",
        "bot_id": "B19LU7CSY",
        "attachments": [
            {
                "text": "This is an attachment",
                "id": 1,
                "fallback": "This is an attachment's fallback"
            }
        ],
        "type": "message",
        "subtype": "bot_message",
        "ts": "1503435956.000247"
    }
}

Typical error response if too many attachments are included

{
    "ok": false,
    "error": "too_many_attachments"
}

The response includes the "timestamp ID" (ts) and the channel-like thing where the message was posted. It also includes the complete message object, as parsed by our servers. This may differ from the provided arguments as our servers sanitize links, attachments, and other properties. Your message may mutate.

Formatting messages

Messages are formatted as described in the formatting spec. You can specify values for parse and link_names to change formatting behavior.

When POSTing with application/x-www-form-urlencoded data, the optional attachments argument should contain a JSON-encoded array of attachments. Make it easy on yourself and send your entire messages as application/json instead.

For more information, see the attachments spec. If you're using a Slack app, you can also use this method to attach message buttons.

By default links to media are unfurled, but links to text content are not. For more information on the differences and how to control this, see the the unfurling documentation.

Use the Message Builder to preview your message formatting and attachments in real time! It's easy to translate your JSON examples to the parameters understood by chat.postMessage.

For best results, limit the number of characters in the text field to 4,000 characters. Ideally, messages should be short and human-readable. Slack will truncate messages containing more than 40,000 characters.

If you need to post longer messages, please consider uploading a snippet instead.

Consider reviewing our message guidelines, especially if you're using attachments or message buttons.

Threads and replies

Provide a thread_ts value for the posted message to act as a reply to a parent message. Sparingly set reply_broadcast to true if your reply is important enough for everyone in the channel to receive.

See message threading for a more in depth look at message threading.

Channels

You must specify a public channel, private channel, or an IM channel with the channel argument. Each one behaves slightly differently based on the authenticated user's permissions and additional arguments:

Post to a public channel

You can either pass the channel's name (#general) or encoded ID (C024BE91L), and the message will be posted to that channel. The channel's ID can be retrieved through the conversations.list API method.

Post to a private group

As long as the authenticated user is a member of the private group, you can either pass the group's name (secret-group) or encoded ID (G012AC86C), and the message will be posted to that group. The private group's ID can be retrieved through the conversations.list API method.

Post to an IM channel

Warning: here be dragons. Posting to an IM channel is a little more complex depending on the value of as_user and the type of token associated with your app.

  • If as_user is false:
    • Pass the IM channel's ID (D023BB3L2) as the value of channel to post to that IM channel as the app, bot, or user associated with the token. You can change the icon and username that go with the message using the icon_url and username parameters. The IM channel's ID can be retrieved through the conversations.list API method.
  • If as_user is true (for workspace apps, this is always the case):
    • Pass the IM channel's ID (D023BB3L2) or a user's ID (U0G9QF9C6) as the value of channel to post to that IM channel as the app, bot, or user associated with the token. The IM channel's ID can be retrieved through the conversations.list API method. When as_user is true, the caller may not manipulate the icon and username on the message. You might receive a channel_not_found error if your app doesn't have permission to enter into an IM with the intended user.

To send a direct message to the user owning the token used in the request, provide the channel field with a conversation/IM ID value found in a method like im.list.

We are phasing out support for ambiguously passing a "username" as a channel value. Please always use channel-like IDs instead.

Begin a conversation in a user's App Home

Start a conversation with users in your App Home.

With the chat:write scope enabled, call chat.postMessage and pass a user's ID (U0G9QF9C6) as the value of channel to post to that user's App Home channel. You can use their direct message channel ID (as found with im.open, for instance) instead.

Rate limiting

chat.postMessage has special rate limiting conditions. It will generally allow an app to post 1 message per second to a specific channel. There are limits governing your app's relationship with the entire workspace above that, limiting posting to several hundred messages per minute. Generous burst behavior is also granted.

Channel membership

New Slack apps do not begin life with the ability to post in all public channels.

For your new Slack app to gain the ability to post in all public channels, request the chat:write.public scope.

Authorship

It's not just copy-paste: new Slack apps also do not begin life with the ability to customize their messages' usernames and icons.

Message authorship refers to who's sending the message: specifically, their username and icon.

New Slack apps customize authorship of their messages by requesting the chat:write.customize scope.

Once you've got permission, provide a username to explicitly specify the username for a message, along with icon_url or icon_emoji.

A helpful hint: new Slack apps don't use the as_user parameter.

The rest of this section only applies to classic Slack apps.

Classic Slack apps using the umbrella bot scope can't request additional scopes to adjust message authorship.

For classic Slack apps, the best way to control the authorship of a message is to be explicit with the as_user parameter.

If you don't use the as_user parameter, chat.postMessage will guess the most appropriate as_user interpretation based on the kind of token you're using.

If as_user is not provided at all, then the value is inferred, based on the scopes granted to the caller: If the caller could post with as_user passed as false, then that is how the method behaves; otherwise, the method behaves as if as_user were passed as true.

When as_user is false

When the as_user parameter is set to false, messages are posted as "bot_messages", with message authorship attributed to the user name and icons associated with the Slack App.

With as_user set to false, you may also provide a username to explicitly specify the bot user's identity for this message, along with icon_url or icon_emoji.

Effect on identity

Token types provide varying default identity values for username, icon_url, and icon_emoji.

Errors

This table lists the expected errors that this method could return. However, other errors can be returned in the case where the service is down or other unexpected factors affect processing. Callers should always check the value of the ok params in the response.

ErrorDescription
channel_not_found

Value passed for channel was invalid.

duplicate_channel_not_found

Channel associated with client_msg_id was invalid.

duplicate_message_not_found

No duplicate message exists associated with client_msg_id.

not_in_channel

Cannot post user messages to a channel they are not in.

is_archived

Channel has been archived.

msg_too_long

Message text is too long

no_text

No message text provided

restricted_action

A workspace preference prevents the authenticated user from posting.

restricted_action_read_only_channel

Cannot post any message into a read-only channel.

restricted_action_thread_only_channel

Cannot post top-level messages into a thread-only channel.

restricted_action_non_threadable_channel

Cannot post thread replies into a non_threadable channel.

too_many_attachments

Too many attachments were provided with this message. A maximum of 100 attachments are allowed on a message.

rate_limited

Application has posted too many messages, read the Rate Limit documentation for more information

as_user_not_supported

The as_user parameter does not function with workspace apps.

ekm_access_denied

Administrators have suspended the ability to post a message.

not_authed

No authentication token provided.

invalid_auth

Some aspect of authentication cannot be validated. Either the provided token is invalid or the request originates from an IP address disallowed from making the request.

account_inactive

Authentication token is for a deleted user or workspace.

token_revoked

Authentication token is for a deleted user or workspace or the app has been removed.

no_permission

The workspace token used in this request does not have the permissions necessary to complete the request. Make sure your app is a member of the conversation it's attempting to post a message to.

org_login_required

The workspace is undergoing an enterprise migration and will not be available until migration is complete.

missing_scope

The token used is not granted the specific scope permissions required to complete this request.

not_allowed_token_type

The token type used in this request is not allowed.

method_deprecated

The method has been deprecated.

deprecated_endpoint

The endpoint has been deprecated.

two_factor_setup_required

Two factor setup is required.

enterprise_is_restricted

The method cannot be called from an Enterprise.

invalid_arguments

The method was either called with invalid arguments or some detail about the arguments passed are invalid, which is more likely when using complex arguments like blocks or attachments.

invalid_arg_name

The method was passed an argument whose name falls outside the bounds of accepted or expected values. This includes very long names and names with non-alphanumeric characters other than _. If you get this error, it is typically an indication that you have made a very malformed API call.

invalid_array_arg

The method was passed an array as an argument. Please only input valid strings.

invalid_charset

The method was called via a POST request, but the charset specified in the Content-Type header was invalid. Valid charset names are: utf-8 iso-8859-1.

invalid_form_data

The method was called via a POST request with Content-Type application/x-www-form-urlencoded or multipart/form-data, but the form data was either missing or syntactically invalid.

invalid_post_type

The method was called via a POST request, but the specified Content-Type was invalid. Valid types are: application/json application/x-www-form-urlencoded multipart/form-data text/plain.

missing_post_type

The method was called via a POST request and included a data payload, but the request did not include a Content-Type header.

team_added_to_org

The workspace associated with your request is currently undergoing migration to an Enterprise Organization. Web API and other platform operations will be intermittently unavailable until the transition is complete.

ratelimited

The request has been ratelimited. Refer to the Retry-After header for when to retry the request.

accesslimited

Access to this method is limited on the current network

request_timeout

The method was called via a POST request, but the POST data was either missing or truncated.

service_unavailable

The service is temporarily unavailable

fatal_error

The server could not complete your operation(s) without encountering a catastrophic error. It's possible some aspect of the operation succeeded before the error was raised.

internal_error

The server could not complete your operation(s) without encountering an error, likely due to a transient issue on our end. It's possible some aspect of the operation succeeded before the error was raised.

Warnings

This table lists the expected warnings that this method will return. However, other warnings can be returned in the case where the service is experiencing unexpected trouble.

WarningDescription
message_truncated

The text field of a message should have no more than 40,000 characters. We truncate really long messages.

missing_charset

The method was called via a POST request, and recommended practice for the specified Content-Type is to include a charset parameter. However, no charset was present. Specifically, non-form-data content types (e.g. text/plain) are the ones for which charset is recommended.

superfluous_charset

The method was called via a POST request, and the specified Content-Type is not defined to understand the charset parameter. However, charset was in fact present. Specifically, form-data content types (e.g. multipart/form-data) are the ones for which charset is superfluous.

Was this page helpful?