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Canon

Vol. VII · Protocols & Tools · VII.3

Agent-to-Agent (A2A)

Google-originated, now Linux Foundation: a protocol for opaque agents to discover, authenticate, and assign tasks across vendors. MCP connects tools. A2A connects firms.

5 min read

a2aproject/A2Agoogle/adk-pythonmodelcontextprotocol/python-sdk

Doctrine

  • Use A2A when the other agent is not in your process — different team, vendor, or trust domain.
  • Inside one process, handoffs or function calls are enough. Do not pay network tax for a crew.
  • Treat remote agents as unreliable tools: timeouts, schemas, auth, budgets.

Interop versus topology

Handoffs are a topology. A2A is a wire protocol for that topology across process boundaries. Google ADK speaks both. If you are not crossing org or vendor lines, stay in-process.

Anti-patterns

  • A2A to two agents that could have been two functions.
  • No identity or audit on cross-agent tasks.

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