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A2A MCP Server

Enables Claude to connect and interact with A2A Protocol agents, allowing discovery of agent capabil...

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Updated Jan 31, 2026
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Enables Claude to connect and interact with A2A Protocol agents, allowing discovery of agent capabilities, sending messages to remote agents, managing multi-turn conversations, and viewing artifacts returned by agents.

  1. Open the FastMCP connection interface

    • Click the "Install Now" button to open the FastMCP / connection UI where environment variables (ENVs) are entered.

  2. Add the required environment variable: A2A_AGENT_CARDS

    • In the FastMCP ENVs panel add a variable named A2A_AGENT_CARDS.
    • The value must be a JSON-stringified list of objects; each object must include a url key (the full Agent Card URL) and may include an optional custom_headers object for authentication headers. Example value (paste this whole string as the ENV value): 
      [{"url":"https://example.com/.well-known/agent-card.json","custom_headers":{"X-API-Key":"YOUR_API_KEY"}}]
    • You can include multiple agents by adding multiple objects in the list (comma-separated). (Format is described in the project README.)

  3. How to obtain an Agent Card URL

    • Option A — Use a public agent: copy the Agent Card URL provided by the agent registry or provider (for example a2anet listings or a demo repository).
    • Option B — If you run the agent yourself: the agent must publish its Agent Card JSON at a well-known path such as https://<your-domain>/.well-known/agent-card.json. Ensure your agent service is reachable at that URL. (a2a-protocol.org)

  4. If the agent requires authentication (API key / token)

    • Get the API key or token from the agent provider (their dashboard or account settings).
    • Place it inside custom_headers in the A2A_AGENT_CARDS list, e.g. 
      [{"url":"https://example.com/.well-known/agent-card.json","custom_headers":{"Authorization":"Bearer YOUR_TOKEN"}}]
    • Use the exact header name the agent expects (e.g., X-API-Key, Authorization).

  5. Verify the Agent Card URL before saving

    • From your terminal, run:
      • curl: curl -sS https://example.com/.well-known/agent-card.json
      • (optional) format with jq: curl -sS https://example.com/.well-known/agent-card.json | jq .
    • The returned JSON should contain top-level metadata such as name, description, url, and a skills array (this confirms the card is valid). (a2a-protocol.org)

  6. Paste the JSON value into FastMCP and save

    • In the FastMCP ENVs UI (opened from "Install Now"), paste the JSON-stringified list as the value for A2A_AGENT_CARDS.
    • Save / Apply the settings in the FastMCP interface.

  7. Start or restart the MCP server

    • Use the FastMCP UI’s install/start action (or restart the MCP) so the server picks up the new ENV.
    • After startup, use the MCP tools list_available_agents to confirm the agent(s) are discoverable.

  8. Troubleshooting tips

    • If list_available_agents fails to show the agent, re-check:
      • The Agent Card URL is reachable from the host (curl from the host).
      • Any custom_headers are correct and accepted by the agent endpoint.
      • The Agent Card JSON is valid and contains skills and url. (a2a-protocol.org)

  9. (Optional) Multiple agents

    • Provide a list with multiple agent objects in the same A2A_AGENT_CARDS value: 
      [{"url":"https://agent1.example/.well-known/agent-card.json"},{"url":"https://agent2.example/.well-known/agent-card.json","custom_headers":{"X-API-Key":"KEY2"}}]
    • Save and restart as above.

  10. Done

    • Once the env is saved and the MCP restarted, use list_available_agents and send_message_to_agent to interact with the configured agents.

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