A2A MCP Server

Instructions

List available agents with their agent cards.

Returns:
    Dict with agents and their cards

Implementation Reference

• a2a_mcp_server/server.py:152-188 (handler)

  The main handler function for the 'list_agents' tool. It iterates over registered A2A servers, fetches agent cards using fetch_agent_card, and returns a dictionary with agent names and their card data.

  async def list_agents() -> Dict[str, Any]:
      """
      List available agents with their agent cards.
      
      Returns:
          Dict with agents and their cards
      """
      try:
          logger.debug("list_agents called")
          logger.debug(f"Current registry: {state.registry}")
          
          # Use the A2ACardResolver to fetch agent cards
          agents = {}
          
          for name, url in state.registry.items():
              try:
                  logger.debug(f"Fetching card for {name} from {url}")
                  card = await fetch_agent_card(url)
                  
                  if card:
                      # Store the card data in a format suitable for JSON response
                      agents[name] = card.model_dump()
                      # Update the cache with the fetched card
                      state.cache[name] = card
                  else:
                      logger.error(f"Failed to fetch agent card for {name}")
              except Exception as e:
                  logger.exception(f"Error fetching card for {name}: {e}")
          
          logger.info(f"Listing {len(agents)} agents")
          return {
              "agent_count": len(agents),
              "agents": agents
          }
      except Exception as e:
          logger.exception(f"Error in list_agents: {str(e)}")
          return {"status": "error", "message": f"Error: {str(e)}"}

• a2a_mcp_server/server.py:152-152 (registration)

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

  async def list_agents() -> Dict[str, Any]:

• a2a_mcp_server/server.py:152-158 (schema)

  The function signature (no input parameters) and docstring define the tool's input/output schema.

  async def list_agents() -> Dict[str, Any]:
      """
      List available agents with their agent cards.
      
      Returns:
          Dict with agents and their cards
      """

• a2a_mcp_server/server.py:46-64 (helper)

  Helper function used by list_agents to fetch an AgentCard from a given A2A server URL.

  async def fetch_agent_card(url: str) -> Optional[AgentCard]:
      """Fetch agent card from an A2A server using A2ACardResolver."""
      try:
          logger.debug(f"Fetching agent card from {url}")
          
          # Use the A2ACardResolver from a2a_min to get the agent card
          card_resolver = A2ACardResolver(url)
          try:
              card = card_resolver.get_agent_card()
              logger.debug(f"Received agent card: {card}")
              return card
          except Exception as e:
              logger.error(f"Failed to fetch agent card: {str(e)}")
              return None
                  
      except Exception as e:
          logger.exception(f"Error fetching agent card from {url}: {e}")
          return None

• a2a_mcp_server/server.py:8-8 (schema)

  Tool description in the module docstring.

  - list_agents: List available agents with their agent cards