Definition
The Agent2Agent Protocol (A2A) is an open standard, introduced by Google in 2025, that defines how autonomous AI agents talk to one another. Where MCP connects an agent to tools and data, A2A connects agents to other agents: discovering what a counterpart can do, delegating a task, streaming status updates, and returning results across organizational and vendor boundaries.
Capability discovery runs through an agent card, a machine-readable description of what an agent offers, how to reach it, and what credentials it requires. Interactions are modeled as tasks with defined lifecycles rather than one-shot API calls, which suits work that takes minutes or hours and needs progress reporting. Other protocols build on this foundation—AP2, for instance, negotiates payment terms over A2A sessions.
A2A matters to GEO because multi-agent systems change how brands are evaluated. When a research agent delegates a subtask to a specialist agent, your content may be assessed by a system you never receive a request from directly, and the brand that reaches the final answer may have been selected several hops upstream. This extends the reasoning behind query fan-out: visibility has to survive not just parallel sub-queries but delegation between agents.
Practically, brands engage with A2A in two ways. Those building agent-facing products publish agent cards so other agents can discover and use their services. Those focused on content treat it as evidence for agent experience optimization: make capabilities, pricing, and facts machine-readable, because the consumer of that information is increasingly another agent rather than a person.
Examples of Agent2Agent Protocol (A2A)
- A travel planning agent delegates hotel availability checks to a specialist booking agent over A2A and streams results back to the user.
- A company publishes an agent card describing its pricing and availability APIs so third-party agents can discover and call them.
- A procurement agent negotiates terms with a supplier agent using A2A messaging before handing settlement to a payments protocol.
- A brand notices AI-driven traffic from agents it never sees directly, because a coordinating agent delegated the retrieval step to another system.
