chat.postMessage

One of these arguments in addition to text is required to describe the content of the message. When attachments or blocks are included, text will be used as fallback text for notifications only.

attachments

string

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

Example

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

blocks

blocks[] as string

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

Example

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

text

string

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

Example

Hello world

Optional arguments

agent_message_source_type

·Optional

Identify how the message was posted for agentforce BE logging

as_user

boolean

·Optional

(Legacy) Pass true to post the message as the authed user instead of as a bot. Defaults to false. Can only be used by classic apps. See legacy as_user parameter below.

Example

true

icon_emoji

string

·Optional

Emoji to use as the icon for this message. Overrides icon_url.

Example

:chart_with_upwards_trend:

icon_url

string

·Optional

URL to an image to use as the icon for this message.

Example

http://lorempixel.com/48/48

link_names

boolean

·Optional

Find and link user groups. No longer supports linking individual users; use syntax shown in Mentioning Users instead.

Example

true

markdown_text

string

·Optional

Accepts message text formatted in markdown. This argument should not be used in conjunction with blocks or text. Limit this field to 12,000 characters.

Example

**This is bold text**

metadata

string

·Optional

JSON object with event_type and event_payload fields, presented as a URL-encoded string. Metadata you post to Slack is accessible to any app or user who is a member of that workspace.

Example

{"event_type": "task_created", "event_payload": { "id": "11223", "title": "Redesign Homepage"}}

mrkdwn

boolean

·Optional

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

Default

true

Example

false

parse

string

·Optional

Change how messages are treated. See below.

Example

full

reply_broadcast

boolean

·Optional

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

Example

true

thread_ts

string

·Optional

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

·Optional

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

Example

true

unfurl_media

boolean

·Optional

Pass false to disable unfurling of media content.

Example

false

username

string

·Optional

Set your bot's user name.

Example

My Bot

Usage info

This method posts a message to a public channel, private channel, or direct message (DM, or IM) conversation.

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

The `text`, `blocks` and `attachments` fields

The usage of the text field changes depending on whether you're using blocks. If you're 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.

It is expected behavior that screen readers will default to the top-level text field of your post, and will not read the content of any interior blocks in the underlying structure of the message. Therefore, to make an accessible app, you must either:

include all necessary content for screen reader users in the top-level text field of your message, or
do not include a top-level text field if the message has blocks, and allow Slack attempt to build it for you by appending content from supported blocks to be read by the screen reader.

JSON POST support

When POSTing with application/x-www-form-urlencoded data, the optional attachments argument should contain a JSON-encoded array of attachments.

As of October 2017, it's 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.

Messages are formatted as described in the formatting spec. The formatting behavior will change depending on the value of parse.

By default, URLs will be hyperlinked. Set parse to none to remove the hyperlinks.

The behavior of parse is different for text formatted with mrkdwn. By default, or when parse is set to none, mrkdwn formatting is implemented. To ignore mrkdwn formatting, set parse to full.

By default, we unfurl all links in any messages posted by users and Slack apps. We also unfurl links to media-based content within Block kit blocks.

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

For more detailed information about link unfurling, refer to unfurling links in messages.

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.

If using blocks, the limit and truncation of characters will be determined by the specific type of block.

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 threading messages 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, as discussed in the sections below.

Pass the channel name or the channel's ID (C123456) 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.

As long as the authenticated user is a member of the private channel, pass the channel's ID (C123456) to the channel parameter and the message will be posted to that channel. The private channel's ID can be retrieved through the conversations.list API method.

As long as the authenticated user is a member of the multi-person direct message (a "private group" or MPIM), you can pass the group's ID (G123456) and the message will be posted to that group. The private group's ID can be retrieved through the conversations.list API method.

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

If you want your app's bot user to start a 1:1 conversation with another user in a workspace, provide the user's ID as the channel value and a direct message conversation will be opened if it isn't open 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 cannot 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 will 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.

A list of user IDs can be retrieved via the users.list API method.

Start a conversation with users in your App Home.

With the chat:write scope enabled, call chat.postMessage and pass a user's ID (U123456) 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 coversations.open, for instance) instead.

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.

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.

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.

To modify the appearance of the app, make calls to chat.postMessage while providing any of the following parameters:

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.

If the channel parameter is set to a User ID (beginning with U), the message will appear in that user's direct message channel with Slackbot. To post a message to that user's direct message channel with the app, use the DM ID (beginning with D) instead.

The chat.delete method has no accommodations for impersonation. If a message is sent impersonating another user, you will not be able to call chat.delete to delete that same message.

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

Information in the section below applies only to classic apps.

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

Legacy `as_user` parameter

For classic apps, the best way to control the authorship of a message was to be explicit with the legacy as_user parameter. If you didn't use the as_user parameter, chat.postMessage would guess the most appropriate as_user interpretation based on the kind of token you were using. If as_user was not provided at all, the value was inferred based on the scopes granted to the caller: If the caller could post with as_user passed as false, then that was how the method behaved; otherwise, the method behaved as if as_user were passed as true.

When the as_user parameter was set to false, messages were posted as "bot_messages", with message authorship attributed to the user name and icons associated with the classic app.

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

Test tokens inherits the icon and username of the token owner.
Slack App user token with chat:write:user inherits the icon and username of the token owner.
Slack App bot user token inherits Slack App's icon and app's bot username.

If using icon_url, icon_emoji, or username with chat.postMessage and a direct message, some special rules apply to ensure the receiver is crystal clear about who is sending the message:

If the legacy as_user argument was false:
- Pass the DM channel's ID (D123456) 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 the legacy as_user parameter was true:
- Pass the DM channel's ID (D123456) or a user's ID (U123456) 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.

Common successful response

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.

{
    "ok": true,
    "channel": "C123ABC456",
    "ts": "1503435956.000247",
    "message": {
        "text": "Here's a message for you",
        "username": "ecto1",
        "bot_id": "B123ABC456",
        "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 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.

Error	Description
`as_user_not_supported`	The `as_user` parameter does not function with workspace apps.
`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`.
`ekm_access_denied`	Administrators have suspended the ability to post a message.
`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.
`invalid_metadata_format`	Invalid metadata format provided
`invalid_metadata_schema`	Invalid metadata schema provided
`is_archived`	Channel has been archived.
`message_limit_exceeded`	Members on this team are sending too many messages. For more details, see https://slack.com/help/articles/115002422943-Usage-limits-for-free-workspaces
`messages_tab_disabled`	Messages tab for the app is disabled.
`metadata_must_be_sent_from_app`	Message metadata can only be posted or updated using an app-level token
`metadata_too_large`	Metadata exceeds size limit
`msg_blocks_too_long`	Blocks submitted with this message are too long.
`no_text`	No message text provided
`not_in_channel`	Cannot post user messages to a channel they are not in.
`rate_limited`	Application has posted too many messages, read the Rate Limit documentation for more information
`restricted_action`	A workspace preference prevents the authenticated user from posting.
`restricted_action_non_threadable_channel`	Cannot post thread replies into a non_threadable channel.
`restricted_action_read_only_channel`	Cannot post any message into a read-only channel.
`restricted_action_thread_locked`	Cannot post replies to a thread that has been locked by admins.
`restricted_action_thread_only_channel`	Cannot post top-level messages into a thread-only channel.
`slack_connect_canvas_sharing_blocked`	Admin has disabled Canvas File sharing in all Slack Connect communications
`slack_connect_file_link_sharing_blocked`	Admin has disabled Slack File sharing in all Slack Connect communications
`slack_connect_lists_sharing_blocked`	Admin has disabled Lists sharing in all Slack Connect communications
`team_access_not_granted`	The token used is not granted the specific workspace access required to complete this request.
`team_not_found`	This error occurs if, when using an org-wide token, the `channel_name` is passed instead of the `channel_id`.
`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.
`cannot_reply_to_message`	This message type cannot have thread replies.
`missing_file_data`	Attempted to share a file but some required data was missing.
`attachment_payload_limit_exceeded`	Attachment payload size is too long.
`markdown_text_conflict`	Markdown text cannot be used in conjunction with `blocks` or `text` argument
`access_denied`	Access to a resource specified in the request is denied.
`account_inactive`	Authentication token is for a deleted user or workspace when using a `bot` token.
`deprecated_endpoint`	The endpoint has been deprecated.
`enterprise_is_restricted`	The method cannot be called from an Enterprise.
`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.
`method_deprecated`	The method has been deprecated.
`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.
`not_authed`	No authentication token provided.
`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.
`token_expired`	Authentication token has expired
`token_revoked`	Authentication token is for a deleted user or workspace or the app has been removed when using a `user` token.
`two_factor_setup_required`	Two factor setup is required.
`accesslimited`	Access to this method is limited on the current network
`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.
`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_arguments`	The method was either called with invalid arguments or some detail about the arguments passed is invalid, which is more likely when using complex arguments like blocks or attachments.
`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.
`ratelimited`	The request has been ratelimited. Refer to the `Retry-After` header for when to retry the request.
`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
`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.

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.

Warning	Description
`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.

API response

URL

POST body

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 instantiates 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 instantiates 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}")

chat.postMessage

Facts

Method access

Required scopes

Content types

Rate limits

Arguments

Usage info

The `text`, `blocks` and `attachments` fields

Accessibility considerations

JSON POST support

Formatting messages

Unfurling content

Truncating content

Threads and replies

Channels

Post to a public channel

Post to a private channel

Post to a multi-person direct message channel

Post to a direct message channel

Getting a user's ID

Begin a conversation in a user's App Home

Rate limiting

Channel membership

Sending messages as other entities

Legacy concerns

Legacy authorship

Legacy `as_user` parameter

Effect on identity

Legacy identity rules in DMs

Example responses

Common successful response

Common error response

Errors

Warnings

Arguments

API response

chat.postMessage

Facts

Method access

Required scopes

Content types

Rate limits

Arguments

Usage info

The text, blocks and attachments fields

Accessibility considerations

JSON POST support

Formatting messages

Unfurling content

Truncating content

Threads and replies

Channels

Post to a public channel

Post to a private channel

Post to a multi-person direct message channel

Post to a direct message channel

Getting a user's ID

Begin a conversation in a user's App Home

Rate limiting

Channel membership

Sending messages as other entities

Legacy concerns

Legacy authorship

Legacy as_user parameter

Effect on identity

Legacy identity rules in DMs

Example responses

Common successful response

Common error response

Errors

Warnings

Arguments

API response

The `text`, `blocks` and `attachments` fields

Legacy `as_user` parameter