A2A Client MCP Server

Instructions

Implementation Reference

• index.ts:246-282 (handler)

  Handler function for the 'a2a_agent_info' tool. Retrieves and returns agent card information for specified or all connected agents.
  case "a2a_agent_info": { const { agentId } = args as { agentId?: string }; if (agentId) { const client = agentManager.getClientById(agentId); if (!client) { throw new Error(`No agent found with ID ${agentId}`); } const card = await client.agentCard(); return { content: [ { type: "text", text: JSON.stringify(card, null, 2), }, ], }; } else { const results = []; for (const [id, client] of agentManager.getAllClients()) { try { const card = await client.agentCard(); results.push({ agentId: id, card }); } catch (error) { results.push({ agentId: id, error: error instanceof Error ? error.message : String(error) }); } } return { content: [ { type: "text", text: JSON.stringify(results, null, 2), }, ], }; } }
• index.ts:117-129 (schema)

  Schema definition for the 'a2a_agent_info' tool, including input schema.
  { name: "a2a_agent_info", description: "Get information about the connected A2A agents", inputSchema: { type: "object", properties: { agentId: { type: "string", description: "Optional agent ID. If not provided, information for all agents will be returned", }, }, }, },
• index.ts:31-131 (registration)

  The tool is registered by being included in the ListToolsRequestHandler response.
  server.setRequestHandler(ListToolsRequestSchema, async () => ({ tools: [ { name: "a2a_send_task", description: "Send a task to an A2A agent", inputSchema: { type: "object", properties: { message: { type: "string", description: "Message to send to the agent", }, taskId: { type: "string", description: "Optional task ID. If not provided, a new UUID will be generated", }, agentId: { type: "string", description: "Optional agent ID. If not provided, the first available agent will be used", }, }, required: ["message"], }, }, { name: "a2a_get_task", description: "Get the current state of a task", inputSchema: { type: "object", properties: { taskId: { type: "string", description: "ID of the task to retrieve", }, agentId: { type: "string", description: "ID of the agent that handled the task", }, }, required: ["taskId", "agentId"], }, }, { name: "a2a_cancel_task", description: "Cancel a running task", inputSchema: { type: "object", properties: { taskId: { type: "string", description: "ID of the task to cancel", }, agentId: { type: "string", description: "ID of the agent that is handling the task", }, }, required: ["taskId", "agentId"], }, }, { name: "a2a_send_task_subscribe", description: "Send a task and subscribe to updates (streaming)", inputSchema: { type: "object", properties: { message: { type: "string", description: "Message to send to the agent", }, taskId: { type: "string", description: "Optional task ID. If not provided, a new UUID will be generated", }, agentId: { type: "string", description: "Optional agent ID. If not provided, the first available agent will be used", }, maxUpdates: { type: "number", description: "Maximum number of updates to receive (default: 10)", }, }, required: ["message"], }, }, { name: "a2a_agent_info", description: "Get information about the connected A2A agents", inputSchema: { type: "object", properties: { agentId: { type: "string", description: "Optional agent ID. If not provided, information for all agents will be returned", }, }, }, }, ], }));
• a2a-client.ts:342-378 (helper)

  The agentCard method in A2AClient class, which fetches the agent card from the A2A server endpoint. This is called by the tool handler.
  async agentCard(): Promise<AgentCard> { try { // First try the well-known endpoint try { const response = await fetch(`${this.baseUrl}/.well-known/agent.json`); if (response.ok) { return response.json(); } } catch (e) { // Ignore and try the next approach } // Then try the traditional endpoint const cardUrl = `${this.baseUrl}/agent-card`; const response = await fetch(cardUrl, { method: "GET", headers: { Accept: "application/json", }, }); if (!response.ok) { throw new Error( `HTTP error ${response.status} fetching agent card from ${cardUrl}: ${response.statusText}` ); } return response.json(); } catch (error) { console.error("Failed to fetch or parse agent card:", error); throw new Error( `Could not retrieve agent card: ${ error instanceof Error ? error.message : String(error) }` ); } }
• a2a-client.ts:101-113 (schema)

  TypeScript interface defining the structure of the AgentCard, which is the output type of the tool.
  export interface AgentCard { name: string; description?: string | null; url: string; provider?: AgentProvider | null; version: string; documentationUrl?: string | null; capabilities: AgentCapabilities; authentication?: AgentAuthentication | null; defaultInputModes?: string[]; defaultOutputModes?: string[]; skills: AgentSkill[]; }