A2A
A2A — the Agent2Agent Protocol — is an open standard that lets independent AI agents find each other and work together, and an agent announces itself with an agent card published at a fixed address on its domain.
Google launched it in April 2025 and it joined the Agentic AI Foundation in August 2026, the same body that governs MCP. Unlike MCP, it does define a file you publish on a domain, which is why it matters to anyone thinking about what their site tells agents.
What is an agent card?
The specification defines it as «a JSON metadata document published by an A2A Server, describing its identity, capabilities, skills, service endpoint, and authentication requirements». It is how one agent finds out what another can do before asking it to do anything.
The recommended location is «/.well-known/agent-card.json» on the server's own domain, which follows RFC 8615, the standard that reserves the `.well-known` path for exactly this kind of declaration.
How is A2A different from MCP?
They solve adjacent problems and are often confused. MCP connects a model to tools and data; A2A connects agents to each other, including agents built by different companies on different stacks that cannot see inside one another.
The specification calls them «independent, potentially opaque AI agent systems», and that word opaque is the point: A2A exists so two agents can cooperate without either revealing how it works.
It took 16 months to make the same move MCP made: launched in April 2025, handed to the foundation in August 2026. Both ended up in the same place, and that convergence is the strongest signal either of them carries.
Does my website need an agent card?
Only if your site offers an agent that other agents should be able to call. A shop, a newspaper or a consultancy does not need one, and publishing an empty one would be worse than publishing none.
It is worth knowing about for a different reason: it is one of the few files in this field that a settled specification actually defines. Most of what gets proposed for `.well-known` has nothing like that behind it.
Where does this come from?
The specification, its repository and the standard that governs the address it uses. All three public.
- A2A specification
The primary source. Both quotations above —the definition of an agent card and the phrase about opaque agent systems— come from here.
- A2A repository
Apache 2.0, version 1.0.0. Useful for checking what changed between versions rather than trusting a summary.
- RFC 8615, Well-Known Uniform Resource Identifiers
The standard that reserves `/.well-known/` for declarations like this one. It is what separates a considered proposal from a file someone invented at a domain root.
Frequently asked questions about A2A
Is A2A a Google protocol?
- A2A started as one, launched in April 2025, and stopped being one in August 2026 when it joined the Agentic AI Foundation under the Linux Foundation. That transition is verifiable and it matters: a protocol governed by a consortium and one owned by a vendor carry different risk.
Does an agent card help AI cite my content?
- No. An agent card declares what an agent can do, not what a page says. Citation depends on whether a crawler can reach your content and quote it, which is a separate layer entirely. Publishing one when you have no agent adds nothing.