Slack MCP Server

Instructions

Implementation Reference

• slack_mcp/server.py:747-793 (handler)

  The handler function for the 'send_formatted_message' MCP tool, decorated with @mcp.tool() for automatic registration. It constructs Slack Block Kit blocks based on input parameters and sends the message via SlackClient, returning JSON result or error.

  @mcp.tool()
  async def send_formatted_message(
      channel: str,
      title: Optional[str] = None,
      text: Optional[str] = None,
      fields: Optional[str] = None,
      context: Optional[str] = None,
      thread_ts: Optional[str] = None
  ) -> str:
      """
      Send a formatted message using Block Kit with common elements.
  
      Args:
          channel: Channel ID or name
          title: Header text (optional)
          text: Main message text (optional)
          fields: Comma-separated fields for side-by-side display (optional)
          context: Context text at bottom (optional)
          thread_ts: Thread timestamp for replies (optional)
      """
      try:
          blocks = []
          
          if title:
              blocks.append(BlockKitBuilder.header(title))
          
          if text:
              blocks.append(BlockKitBuilder.section(text))
          
          if fields:
              field_list = [field.strip() for field in fields.split(",")]
              blocks.append(BlockKitBuilder.fields_section(field_list))
          
          if context:
              blocks.append(BlockKitBuilder.context([context]))
          
          if not blocks:
              return json.dumps({"error": "At least one of title, text, fields, or context must be provided"}, indent=2)
          
          fallback_text = title or text or "Formatted message"
          
          client = SlackClient()
          result = await client.send_message(channel, fallback_text, thread_ts, blocks)
          return json.dumps(result, indent=2)
      except Exception as e:
          return json.dumps({"error": str(e)}, indent=2)

• slack_mcp/server.py:747-747 (registration)

  The @mcp.tool() decorator registers the send_formatted_message function as an MCP tool.

  @mcp.tool()

• slack_mcp/server.py:749-754 (schema)

  Input schema defined by function type hints and default values, used by MCP for tool parameter schema.

  channel: str,
  title: Optional[str] = None,
  text: Optional[str] = None,
  fields: Optional[str] = None,
  context: Optional[str] = None,
  thread_ts: Optional[str] = None