Slack MCP Server

Instructions

Implementation Reference

• src/index.ts:40-52 (handler)

  Handler for the slack_post_message tool within the CallToolRequest switch statement. It validates the input arguments, calls slackClient.postMessage, and returns the JSON-stringified 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) }],
    };
  }

• src/slack/messages.ts:8-25 (schema)

  Tool definition including name, description, and input schema for slack_post_message.

  export 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 Channel ID to post the message to",
        },
        text: {
          type: "string",
          description: "The message text to post",
        },
      },
      required: ["channel_id", "text"],
    },
  };

• src/index.ts:25-29 (registration)

  Registration of the slack_post_message tool (via postMessageTool) in the ListToolsRequest handler.

  server.setRequestHandler(ListToolsRequestSchema, async () => {
    return {
      tools: [getUsersTool, postMessageTool],
    };
  });

• src/slack/client.ts:34-45 (helper)

  Core helper function in SlackClient that performs the HTTP POST to Slack's chat.postMessage API.

  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();
  }

• src/slack/messages.ts:3-6 (schema)

  TypeScript interface defining the input arguments for the slack_post_message tool.

  export interface PostMessageArgs {
    channel_id: string;
    text: string;
  }