slack_post_message
Send messages to Slack channels using the MCP Server for Slack. This tool enables AI assistants to communicate directly within Slack workspaces by posting text content to specified channels.
Instructions
Post a new message to a Slack channel
Input Schema
TableJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| channel_id | Yes | The ID of the channel to post to | |
| text | Yes | The message text to post |
Implementation Reference
- index.ts:433-447 (handler)The main handler for the slack_post_message tool within the CallToolRequest switch statement. It validates the required arguments (channel_id and text), calls SlackClient.postMessage, and returns the API response.case "slack_post_message": { const args = request.params.arguments as unknown as PostMessageArgs; if (!args.channel_id || !args.text) { throw new Error( "Missing required arguments: channel_id and text", ); } const response = await slackClient.postMessage( args.channel_id, args.text, ); return { content: [{ type: "text", text: JSON.stringify(response) }], }; }
- index.ts:74-91 (schema)Tool schema definition for slack_post_message, specifying name, description, input properties (channel_id, text), and required fields.const postMessageTool: Tool = { name: "slack_post_message", description: "Post a new message to a Slack channel", inputSchema: { type: "object", properties: { channel_id: { type: "string", description: "The ID of the channel to post to", }, text: { type: "string", description: "The message text to post", }, }, required: ["channel_id", "text"], }, };
- index.ts:273-284 (helper)Helper method in SlackClient class that performs the actual Slack API call to post a message using chat.postMessage endpoint.async postMessage(channel_id: string, text: string): Promise<any> { const response = await fetch("https://slack.com/api/chat.postMessage", { method: "POST", headers: this.botHeaders, body: JSON.stringify({ channel: channel_id, text: text, }), }); return response.json(); }
- index.ts:567-582 (registration)Registration of the tool via inclusion of postMessageTool in the tools list returned by the ListToolsRequest handler.server.setRequestHandler(ListToolsRequestSchema, async () => { console.log("Received ListToolsRequest"); return { tools: [ listChannelsTool, postMessageTool, replyToThreadTool, addReactionTool, getChannelHistoryTool, getThreadRepliesTool, getUsersTool, getUserProfileTool, lookupUserByEmailTool, ], }; });
- index.ts:17-20 (schema)TypeScript interface defining the input arguments for the slack_post_message tool.interface PostMessageArgs { channel_id: string; text: string; }