What Is A2A (Agent2Agent)? Definition

What is A2A (Agent2Agent)?

A2A stands for Agent2Agent, an open protocol that defines how AI agents communicate with each other. It sets out how one agent discovers another, addresses it and delegates tasks to it, no matter which vendor or framework the agents come from.

Google started A2A and later handed it over to the Linux Foundation, so it can develop further as a vendor-neutral open standard. Technically, A2A is built on JSON-RPC, an established, lightweight format for remote function calls.

Example: a travel assistant needs a hotel room. Its agent reads the hotel's agent card, sees that the hotel's own agent can check availability and take bookings, and sends it the request over JSON-RPC. The hotel's agent replies with the available rooms.

How does A2A work?

At the center of A2A is the agent card, a machine-readable description of an agent. It usually sits at the path /.well-known/agent-card.json and describes who the agent is and what it can do. The process:

• Discovery – an agent reads another agent's card and learns its capabilities.
• Communication – tasks are handed over and results are returned via JSON-RPC.
• Delegation – complex tasks are coordinated across several specialized agents.

What role does A2A play in the agentic web?

A2A is one of the core protocols of the agentic web. The Model Context Protocol (MCP) governs how an agent accesses the tools and data of an application. A2A governs how agents talk to each other. The two complement each other.

For companies, this means: if you publish your own agent card at /.well-known/agent-card.json, other agents can find you and give you tasks. That is a core part of agent readiness (AAO), and it is the reason A2A matters for AI search: an agent can only recommend or contact a business it can discover and understand. Our guide on optimizing your website for AI agents covers the practical steps.

A2A in practice at SEOX

At SEOX, we use A2A as part of our agent readiness work, both on our own website and in client projects. The goal is that a company is found in the agentic web, and also understood correctly and addressed in a useful way.