Slack MCP Server

Instructions

Implementation Reference

• slack_mcp/server.py:310-327 (handler)

  MCP tool handler implementation for 'update_message'. Creates a SlackClient instance, parses optional blocks JSON, calls the client's update_message method, and returns the JSON-formatted result or error.

  @mcp.tool()
  async def update_message(channel: str, ts: str, text: str, blocks: Optional[str] = None) -> str:
      """
      Update an existing Slack message.
  
      Args:
          channel: Channel ID where the message exists
          ts: Timestamp of the message to update
          text: New message text (fallback text for notifications)
          blocks: JSON string of Block Kit blocks for rich formatting
      """
      try:
          client = SlackClient()
          blocks_data = json.loads(blocks) if blocks else None
          result = await client.update_message(channel, ts, text, blocks_data)
          return json.dumps(result, indent=2)
      except Exception as e:
          return json.dumps({"error": str(e)}, indent=2)

• slack_mcp/server.py:116-125 (helper)

  SlackClient helper method that constructs the request payload and calls Slack API endpoint 'chat.update' via _make_request to update the message.

  async def update_message(
      self, channel: str, ts: str, text: str, blocks: Optional[List[Dict[str, Any]]] = None
  ) -> Dict[str, Any]:
      """Update an existing message."""
      data = {"channel": channel, "ts": ts, "text": text}
  
      if blocks:
          data["blocks"] = blocks
  
      return await self._make_request("POST", "chat.update", json_data=data)

• slack_mcp/server.py:310-310 (registration)

  The @mcp.tool() decorator registers the update_message function as an MCP tool with FastMCP instance.

  @mcp.tool()