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Sends a message to a channel.


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

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


Argument Example Required Description

Authentication token bearing required scopes.


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

textHello worldRequired

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


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.

attachments[{"pretext": "pre-hello", "text": "text-world"}]Optional

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

blocks[{"type": "section", "text": {"type": "plain_text", "text": "Hello world"}}]Optional

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


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.


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.


Find and link channel names and usernames.

mrkdwnfalseOptional, default=true

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


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


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


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


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


Pass false to disable unfurling of media content.

usernameMy BotOptional

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

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.


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.


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 channels.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 groups.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 im.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 im.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, 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.


The as_user parameter may not be used by new Slack apps (i.e., apps installed using our V2 of Oauth 2.0). New Slack apps act on their own behalf, rather than a user's.

For older Slack apps, message authorship and attribution varies. The rest of this Authorship section applies only to classic Slack apps.

The best way to control the authorship of a message is to be explicit with the as_user parameter.

Otherwise, 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.


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.


Value passed for channel was invalid.


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


Channel has been archived.


Message text is too long


No message text provided


A workspace preference prevents the authenticated user from posting.


Cannot post any message into a read-only channel.


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


Cannot post thread replies into a non_threadable channel.


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


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


The as_user parameter does not function with workspace apps.


Administrators have suspended the ability to post a message.


No authentication token provided.


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.


Authentication token is for a deleted user or workspace.


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


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.


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


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


The method was called with invalid arguments.


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.


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.


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.


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.


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


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.


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


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.


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.


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


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.


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.