ADK Protocols: MCP and A2A

One ADK agent, two integration surfaces — MCP consumes tools, A2A calls remote agents

ADK Protocols: MCP and A2A One ADK agent, two integration surfaces — MCP consumes tools, A2A calls remote agents MCP surface — tools A2A surface — agents User · prompt · Architecture component User prompt ADK Agent · LlmAgent · Architecture component · tools + peers ADK Agent LlmAgent tools + peers MCPToolset · tool adapter · MCP surface — tools · list / call MCPToolset tool adapter list / call MCP Server · stdio / SSE · MCP surface — tools · tools MCP Server stdio / SSE tools A2A Client · agent card · A2A surface — agents · discovery A2A Client agent card discovery Remote Agent · A2A / HTTP · A2A surface — agents · peer Remote Agent A2A / HTTP peer prompt call tool send task Legend External Backend Security

MCP — for tools

  • • MCPToolset mounts an external tool server
  • • Tools are discovered and invoked as function calls
  • • Transport is stdio or SSE, outside the agent process

A2A — for agents

  • • The agent discovers a peer via its agent card
  • • Work is delegated to a remote agent over HTTP
  • • The peer runs its own model and tools independently

Two surfaces

  • • MCP integrates capabilities; A2A integrates agents
  • • Both hang off the same ADK agent
  • • Each boundary can fail or scale on its own

Architecture diagram • Built with Archify • Create yours ↗ • Hover to trace • R route • Click to focus • +/− zoom • M radar • [/] views • P play story • T theme • E export