A2A Explained: The Agent-to-Agent Protocol
Depth · Core
Good for: Builders
A2A, the Agent-to-Agent protocol, is an open standard for AI agents to communicate and delegate tasks to one another. It originated at Google and is now stewarded under the Linux Foundation. In the context of agentic commerce it is best understood as a coordination layer: it is not a commerce protocol in itself, but the substrate that buyer and merchant agents use to talk, and that payment standards build on.
Its role in commerce
A2A shows up underneath the payment layer rather than at the checkout. Two connections matter. First, AP2, the payment-authorization standard, is built as an extension of A2A, so the signed-mandate machinery rides on top of agent-to-agent messaging. Second, an A2A x402 extension brings x402-style stablecoin payments to agent-to-agent interactions, built by Google with Coinbase, the Ethereum Foundation, and MetaMask. In both cases A2A handles how the agents coordinate, and the commerce or payment specifics live in an extension on top.
How to hold it in your head
Keep the layers separate: A2A is how agents talk and delegate, MCP is how an agent discovers tools, and the commerce and payment protocols (ACP, UCP, AP2, x402, MPP) run the actual transaction on top. A2A is the most behind-the-scenes of the agentic commerce acronyms, which is why it usually appears as a foundation other protocols extend rather than something a merchant integrates directly. For the full map, see the protocol stack.
FAQ
What is A2A? An open standard for agents to communicate and delegate to one another, originated at Google and now under the Linux Foundation. It is a coordination layer, not a commerce protocol.
What does it have to do with agentic commerce? It is the substrate payment extensions build on: AP2 is an A2A extension, and an A2A x402 extension adds stablecoin payments. A2A handles agent coordination; commerce rides on top.
Is A2A a payment protocol? No. Payments ride on top of A2A through extensions like AP2 and the A2A x402 extension, rather than being part of A2A itself.