Slack: Sends a message to a channel

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Operation slack.chat_postmessage

Provider route: POST /chat.postMessage. Alter supplies the connection’s credentials and routing.

Call through Alter

Install @alter-ai/sdk @alter-ai/slack with npm, or alter-sdk-slack with pip. Supply your connected customer’s grant ID and the arguments described below.

import { App } from "@alter-ai/sdk";
import { SlackIntegration } from "@alter-ai/slack";

async function execute(input: Parameters<SlackIntegration["chat"]["postMessage"]>[0]) {
  const app = new App({ apiKey: process.env.ALTER_API_KEY! });
  try {
    const provider = new SlackIntegration(app, { grantId: process.env.PROVIDER_GRANT_ID! });
    const call = await provider.chat.postMessage(input);
    const result = await call.wait();
    return result.bodyJson();
  } finally {
    await app.close();
  }
}

import os
from alter_sdk import App
from alter_sdk_slack import SlackIntegration

async def execute(arguments):
    async with App(api_key=os.environ["ALTER_API_KEY"]) as app:
        provider = SlackIntegration(app, {"grant_id": os.environ["PROVIDER_GRANT_ID"]})
        call = await provider.chat.post_message(arguments)
        result = await call.wait()
        return result.body_json()

Input

Field	Type	Presence	Description and constraints
$	object	Root	Additional keys: not allowed
body	object	Required within parent
body.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.
body.attachments	string	Optional	A JSON-based array of structured attachments, presented as a URL-encoded string.
body.blocks	string	Optional	A JSON-based array of structured blocks, presented as a URL-encoded string.
body.channel	string	Required within parent	An encoded ID or channel name that represents a channel, private group, or IM channel to send the message to.
body.current_draft_last_updated_ts	string	Optional	This field represents the timestamp of the draft’s last update at the time this API is called. If the current message is a draft, this field can be provided to ensure synchronization with the server.
body.icon_emoji	string	Optional	Emoji to use as the icon for this message. Overrides `icon_url`.
body.icon_url	string	Optional	URL to an image to use as the icon for this message.
body.link_names	boolean	Optional	Find and link user groups. No longer supports linking individual users; use syntax shown in Mentioning Users instead.
body.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.
body.metadata	string	Optional	JSON object with event_type and event_payload fields, presented as a URL-encoded string. You can also provide Work Object entity metadata using this parameter. Metadata you post to Slack is accessible to any app or user who is a member of that workspace.
body.mrkdwn	boolean	Optional	Disable Slack markup parsing by setting to `false`. Enabled by default.
body.parse	string	Optional	Change how messages are treated.
body.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`.
body.text	string	Optional	How this field works and whether it is required depends on other fields you use in your API call.
body.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.
body.unfurl_app_links	boolean	Optional	Pass true to unfurl links from installed apps, or false to prevent app links from unfurling. When omitted, app links follow the `unfurl_links` setting.
body.unfurl_links	boolean	Optional	Pass true to enable unfurling of primarily text-based content.
body.unfurl_media	boolean	Optional	Pass false to disable unfurling of media content.
body.username	string	Optional	Set your bot’s user name.

Response

Response media type: application/json. The table describes the pinned successful response. Referenced models link to their complete fields.

Field	Type	Presence	Description and constraints
$	object	Root	Schema for successful response of chat.postMessage method
channel	string	Optional
message	Model	Optional	Expand Sends a message to a channel — response body — message
ok	boolean	Required within parent	Must equal: true
ts	string	Optional

Referenced models: Sends a message to a channel — response body — message

Schemas

2 more schemas are linked from the tables above, on the schema pages.

Sends a message to a channel — response body — message

Field	Type	Presence	Description and constraints
$	object	Root
attachments	array	Optional
attachments[]	object	Each item
attachments[].fallback	string	Optional
attachments[].id	JSON	Optional
attachments[].id (anyOf 1)	integer	Alternative
attachments[].id (anyOf 2)	string	Alternative	Pattern: ^-?[0-9]+(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?$
attachments[].image_bytes	JSON	Optional
attachments[].image_bytes (anyOf 1)	integer	Alternative
attachments[].image_bytes (anyOf 2)	string	Alternative	Pattern: ^-?[0-9]+(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?$
attachments[].image_height	JSON	Optional
attachments[].image_height (anyOf 1)	integer	Alternative
attachments[].image_height (anyOf 2)	string	Alternative	Pattern: ^-?[0-9]+(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?$
attachments[].image_url	string	Optional
attachments[].image_width	JSON	Optional
attachments[].image_width (anyOf 1)	integer	Alternative
attachments[].image_width (anyOf 2)	string	Alternative	Pattern: ^-?[0-9]+(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?$
blocks	Model	Optional	Expand Sends a message to a channel — response body — message blocks
bot_id	JSON	Optional
bot_id (anyOf 1)	string	Alternative
bot_id (anyOf 2)	null	Alternative
bot_profile	Model	Optional	Expand Sends a message to a channel — response body — message bot profile
client_msg_id	string	Optional
comment	Model	Optional	Expand Sends a message to a channel — response body — message comment
display_as_bot	boolean	Optional
file	Model	Optional	Expand Gets information about a file — response body — file
files	array	Optional
files[]	Model	Each item	Expand Gets information about a file — response body — file
icons	object	Optional
icons.emoji	string	Optional
icons.image_64	string	Optional	Format: uri
inviter	string	Optional
is_delayed_message	boolean	Optional
is_intro	boolean	Optional
is_starred	boolean	Optional
last_read	string	Optional
latest_reply	string	Optional
name	string	Optional
old_name	string	Optional
parent_user_id	string	Optional
permalink	string	Optional	Format: uri
pinned_to	array	Optional
pinned_to[]	string	Each item
purpose	string	Optional
reactions	array	Optional
reactions[]	Model	Each item	Expand Gets information about a file — response body — file reactions item
reply_count	JSON	Optional
reply_count (anyOf 1)	integer	Alternative
reply_count (anyOf 2)	string	Alternative	Pattern: ^-?[0-9]+(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?$
reply_users	array	Optional
reply_users[]	string	Each item
reply_users_count	JSON	Optional
reply_users_count (anyOf 1)	integer	Alternative
reply_users_count (anyOf 2)	string	Alternative	Pattern: ^-?[0-9]+(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?$
source_team	string	Optional
subscribed	boolean	Optional
subtype	string	Optional
team	string	Optional
text	string	Optional
thread_ts	string	Optional
topic	string	Optional
ts	string	Optional
type	string	Optional
unread_count	JSON	Optional
unread_count (anyOf 1)	integer	Alternative
unread_count (anyOf 2)	string	Alternative	Pattern: ^-?[0-9]+(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?$
upload	boolean	Optional
user	string	Optional
user_profile	Model	Optional	Expand Sends a message to a channel — response body — message user profile
user_team	string	Optional
username	string	Optional

Referenced models: Sends a message to a channel — response body — message blocks, Sends a message to a channel — response body — message bot profile, Sends a message to a channel — response body — message comment, Gets information about a file — response body — file, Gets information about a file — response body — file reactions item, Sends a message to a channel — response body — message user profile

Sends a message to a channel — response body — message blocks

Field	Type	Presence	Description and constraints
$	array	Root	This is a very loose definition, in the future, we'll populate this with deeper schema in this definition namespace.
$[]	object	Each item	Additional keys: allowed
$[].type	string	Optional

Sends a message to a channel — response body — message bot profile

Field	Type	Presence	Description and constraints
$	object	Root
app_id	string	Optional
deleted	boolean	Optional
icons	object	Optional
icons.image_36	string	Optional	Format: uri
icons.image_48	string	Optional	Format: uri
icons.image_72	string	Optional	Format: uri
id	string	Optional
name	string	Optional
team_id	string	Optional
updated	JSON	Optional
updated (anyOf 1)	integer	Alternative
updated (anyOf 2)	string	Alternative	Pattern: ^-?[0-9]+(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?$

Sends a message to a channel — response body — message comment

Field	Type	Presence	Description and constraints
$	object	Root
comment	string	Optional
created	JSON	Optional
created (anyOf 1)	integer	Alternative
created (anyOf 2)	string	Alternative	Pattern: ^-?[0-9]+(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?$
id	string	Optional
is_intro	boolean	Optional
is_starred	boolean	Optional
num_stars	JSON	Optional
num_stars (anyOf 1)	integer	Alternative
num_stars (anyOf 2)	string	Alternative	Pattern: ^-?[0-9]+(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?$
pinned_info	Model	Optional	Expand Gets information about a file — response body — file pinned info
pinned_to	array	Optional
pinned_to[]	string	Each item
reactions	array	Optional
reactions[]	Model	Each item	Expand Gets information about a file — response body — file reactions item
timestamp	JSON	Optional
timestamp (anyOf 1)	integer	Alternative
timestamp (anyOf 2)	string	Alternative	Pattern: ^-?[0-9]+(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?$
user	string	Optional

Referenced models: Gets information about a file — response body — file pinned info, Gets information about a file — response body — file reactions item

Gets information about a file — response body — file reactions item

Field	Type	Presence	Description and constraints
$	object	Root	Additional keys: allowed
count	JSON	Optional
count (anyOf 1)	integer	Alternative
count (anyOf 2)	string	Alternative	Pattern: ^-?[0-9]+(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?$
name	string	Optional
users	array	Optional
users[]	string	Each item

Gets information about a file — response body — file pinned info

Field	Type	Presence	Description and constraints
$	object	Root

Policy, approvals and errors

SDK function policy ID: slack.chat_postmessage. Catalog operation: chat_postMessage. Rules can name either ID; function rules distinguish managed calls and conservatively cover raw calls sharing the route. Existing grant permissions and policy rules apply. wait() returns an immediate result or waits for a required approval; it never approves the request itself. Persist the approval ID to resume after a restart.

Provider errors retain their response; JSON decoding raises ProviderAPIError for provider failures. ManagedOperationError identifies contract/input/retention errors. See error handling and provider-specific behavior. Sensitive input may be refused before approval storage. A decoding error never resubmits a write.

Required provider scopes: ["chat:write"]

Official provider source