Sends a message to a channel.

Facts

Method access

HTTP
JavaScript
Python
Java
HTTP
POSThttps://slack.com/api/chat.postMessage
Bolt for Java
app.client().chatPostMessage
Powered by Bolt
Bolt for Python
app.client.chat_postMessage
Powered by Bolt
Bolt for JavaScript
app.client.chat.postMessage
Powered by Bolt

Content types

application/x-www-form-urlencodedapplication/json
  • Rate limits

    Special
  • Arguments

    ArgumentTypeDescription
    tokenRequired

    Authentication token bearing required scopes. Tokens should be passed as an HTTP Authorization header or alternatively, as a POST parameter.

    Examplexxxx-xxxxxxxxx-xxxx
    channelRequired
    string

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

    ExampleC1234567890
    as_user
    boolean

    Pass true to post the message as the authed user, instead of as a bot. Defaults to false. See authorship below.

    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.

    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.

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

    Find and link channel names and usernames.

    Exampletrue
    mrkdwn
    boolean

    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
    boolean

    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
    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
    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.

    unfurl_links
    boolean

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

    Exampletrue
    unfurl_media
    boolean

    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.

    Example responses

    Common successful 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"
        }
    }
    Common error response

    Typical error response if too many attachments are included

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

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

    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.

    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. Links found in blocks will also be unfurled by default.

    If you want to suppress link unfurls in messages containing blocks, set unfurl_links and unfurl_media to false. 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

    Pass the channel's ID (C024BE91L) to the channel parameter 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 multi-person direct message

    As long as the authenticated user is a member of the multi-person direct message (AKA "private group" or MPIM), you can pass the group's 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 a direct message channel

    Posting to direct messages (also known as DMs or IMs) can be a little more complex, depending on what you actually are meaning to accomplish.

    If you simply want your app's bot user to start a 1:1 conversation with another user in a workspace, provide the user's user ID as the channel value and a direct message conversation will be opened, if it hasn't already. Resultant messages and associated direct message objects will have a direct message ID you can use from that point forward, if you'd rather.

    Bot users can't post to a direct message conversation between two users using chat.postMessage. If your app was involved in the conversation, then it would be a multi-person direct message instead. Apps can post to direct message conversations between users when a shortcut or slash command belonging to that app is used in the conversation.

    You might receive a channel_not_found error if your app doesn't have permission to enter into a DM with the intended user.

    Passing a "username" as a channel value is deprecated, along with the whole concept of usernames on Slack. Please always use channel-like IDs instead to make sure your message gets to where it's going.

    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.


    Sending messages as other entities

    Apps can publish messages that appear to have been created by a user in the conversation. The message will be attributed to the user and show their profile photo beside it.

    This is a powerful ability and must only be used when the user themselves gives permission to do so. For this reason, this ability is only available when an app has requested and been granted an additional scope — chat:write.customize.

    Your app should only use this feature in response to an inciting user action. It should never be unexpected or surprising to a user that a message was posted on their behalf, and it should be heavily signposted in advance.

    With all that in mind, the act of authoring a message as a user is relatively simple. With the aforementioned scope, you'll be able to make calls to chat.postMessage and provide:

    • username to specify the username for the published message.
    • icon_url to specify a URL to an image to use as the profile photo alongside the message.
    • icon_emoji to specify an emoji (using colon shortcodes, eg. :white_check_mark:) to use as the profile photo alongside the message.

    This feature works differently for classic Slack apps, see below for more details.


    Legacy concerns

    Information in the section below applies only to classic Slack apps.

    Legacy authorship

    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.

    Legacy identity rules in DMs

    If you're using icon_url, icon_emoji, or username with chat.postMessage and a direct message, some special rules apply to make sure the receiver is crystal clear on just who is sending the message:

    • If as_user is false:
      • Pass the DM channel's ID (D023BB3L2) as the value of channel to post to that DM 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:
      • Pass the DM channel's ID (D023BB3L2) or a user's ID (U0G9QF9C6) as the value of channel to post to that DM 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.

    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.

    restricted_action_thread_locked

    Cannot post replies to a thread that has been locked by admins.

    too_many_attachments

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

    too_many_contact_cards

    Too many contact_cards were provided with this message. A maximum of 10 contact cards 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.

    slack_connect_file_link_sharing_blocked

    Admin has disabled Slack File sharing in all Slack Connect communications

    invalid_blocks

    Blocks submitted with this message are not valid

    invalid_blocks_format

    The blocks is not a valid JSON object or doesn't match the Block Kit syntax.

    team_access_not_granted

    The token used is not granted the specific workspace access required to complete this request.

    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 when using a bot token.

    token_revoked

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

    token_expired

    Authentication token has expired

    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.

    Arguments

    Need a token? Create and install a Slack app to begin.
    This will make a real API request. Beware of using it with live workspaces.

    API response


    Submit your arguments to see the API response
    Calling chat.postMessage
    Java
    JavaScript
    Python
    Java
    import com.slack.api.bolt.App;
    import com.slack.api.bolt.AppConfig;
    import com.slack.api.bolt.jetty.SlackAppServer;
    import com.slack.api.methods.SlackApiException;
    
    import java.io.IOException;
    
    public class ChatPostMessage {
    
        public static void main(String[] args) throws Exception {
            var config = new AppConfig();
            config.setSingleTeamBotToken(System.getenv("SLACK_BOT_TOKEN"));
            config.setSigningSecret(System.getenv("SLACK_SIGNING_SECRET"));
            var app = new App(config); // `new App()` does the same
    
            app.message("hello", (req, ctx) -> {
                var logger = ctx.logger;
                try {
                    var event = req.getEvent();
                    // Call the chat.postMessage method using the built-in WebClient
                    var result = ctx.client().chatPostMessage(r -> r
                        // The token you used to initialize your app is stored in the `context` object
                        .token(ctx.getBotToken())
                        // Payload message should be posted in the channel where original message was heard
                        .channel(event.getChannel())
                        .text("world")
                    );
                    logger.info("result: {}", result);
                } catch (IOException | SlackApiException e) {
                    logger.error("error: {}", e.getMessage(), e);
                }
                return ctx.ack();
            });
    
            var server = new SlackAppServer(app);
            server.start();
        }
    }
    
    JavaScript
    Code to initialize Bolt app
    // Require the Node Slack SDK package (github.com/slackapi/node-slack-sdk) const { WebClient, LogLevel } = require("@slack/web-api"); // WebClient insantiates a client that can call API methods // When using Bolt, you can use either `app.client` or the `client` passed to listeners. const client = new WebClient("xoxb-your-token", { // LogLevel can be imported and used to make debugging simpler logLevel: LogLevel.DEBUG });
    // ID of the channel you want to send the message to const channelId = "C12345"; try { // Call the chat.postMessage method using the WebClient const result = await client.chat.postMessage({ channel: channelId, text: "Hello world" }); console.log(result); } catch (error) { console.error(error); }
    Python
    Code to initialize Bolt app
    import logging import os # Import WebClient from Python SDK (github.com/slackapi/python-slack-sdk) from slack_sdk import WebClient from slack_sdk.errors import SlackApiError # WebClient insantiates a client that can call API methods # When using Bolt, you can use either `app.client` or the `client` passed to listeners. client = WebClient(token=os.environ.get("SLACK_BOT_TOKEN")) logger = logging.getLogger(__name__)
    # ID of the channel you want to send the message to channel_id = "C12345" try: # Call the chat.postMessage method using the WebClient result = client.chat_postMessage( channel=channel_id, text="Hello world" ) logger.info(result) except SlackApiError as e: logger.error(f"Error posting message: {e}")

    Was this page helpful?