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Sends a message to a channel.

An MCP tool from the Slack API server, hosted on mcp.hjlabs.in.

Sends a message to a channel. [POST /chat.postMessage]

Name on the gateway: slack_api__chat_post_message · may change things.

Parameters

Name	Type	Description
`as_user`	`string`	Pass true to post the message as the authed user, instead of as a bot.…
`attachments`	`string`	A JSON-based array of structured attachments, presented as a URL-encoded string.
`blocks`	`string`	A JSON-based array of structured blocks, presented as a URL-encoded string.
`channel` required	`string`	Channel, private group, or IM channel to send message to. Can be an encoded…
`icon_emoji`	`string`	Emoji to use as the icon for this message. Overrides icon_url. Must be used in…
`icon_url`	`string`	URL to an image to use as the icon for this message. Must be used in…
`link_names`	`boolean`	Find and link channel names and usernames.
`mrkdwn`	`boolean`	Disable Slack markup parsing by setting to false. Enabled by default.
`parse`	`string`	Change how messages are treated. Defaults to none. See below.
`reply_broadcast`	`boolean`	Used in conjunction with thread_ts and indicates whether reply should be made…
`text`	`string`	How this field works and whether it is required depends on other fields you…
`thread_ts`	`string`	Provide another message's ts value to make this message a reply. Avoid using a…
`unfurl_links`	`boolean`	Pass true to enable unfurling of primarily text-based content.
`unfurl_media`	`boolean`	Pass false to disable unfurling of media content.
`username`	`string`	Set your bot's user name. Must be used in conjunction with as_user set to…

Through the Smart Gateway, any client can run it by name with call_tool, or let the gateway find it with search_tools:

call_tool arguments

{
  "name": "slack_api__chat_post_message",
  "arguments": {
    "channel": "…"
  }
}

Or connect the Slack API server directly, which lists 174 tools including this one:

Run in your terminal

claude mcp add --transport http hj-slack-api https://mcp.hjlabs.in/mcp/slack-api \
  --header "Authorization: Bearer YOUR_API_KEY"

Use the sends a message to a channel. tool with as_user set to ….