Agent Card
Before one agent can hand work to another, it has to know what that other agent can actually do and how to reach it. An Agent Card is the small machine-readable document that answers precisely that.
What the card declares
Defined by the Agent2Agent (A2A) protocol, the card is a JSON document published at a well-known address on the agent's own domain, so discovery needs no central registry. It states:
- Identity — name, version and a human-readable description of purpose.
- Skills: the discrete jobs the agent accepts, with example inputs.
- The service endpoint, the transports it speaks, and the content types it can exchange.
- Authentication requirements — what credential a caller must present.
How it is used during a run
A client agent fetches the card, matches the task in hand against the advertised skills, and only then opens a task with that agent; if nothing matches it looks elsewhere or does the work itself. The card plays the role an OpenAPI document plays for web APIs, or a tool listing plays for a Model Context Protocol server — with the difference that the counterparty is another autonomous loop rather than a fixed function.
Why it matters
Without cards, every multi-agent system is wired by hand and re-wired whenever a peer changes. With them, delegation becomes late-bound: agents built by different teams on different frameworks find each other at run time. The matching failure mode is a stale or over-claiming card — work gets routed to an agent that cannot complete it, and the caller discovers this only after the task fails.
An Agent Card is the machine-readable descriptor an agent publishes under the Agent2Agent protocol, declaring its identity, endpoint, skills, and authentication requirements. It is served at a well-known URL so other agents can discover what a peer can do before delegating work to it. Without such a descriptor, inter-agent collaboration requires hard-coded knowledge of every participant, which does not scale beyond a fixed set.
When tradespeople meet on a job they swap business cards: here is my name, here is what I do, here is how to reach me. An Agent Card is that card, written for software.
As more AI helpers start working on their own, they need to pass jobs to each other — one handles travel bookings, another handles expenses. The card is a small file each helper publishes, saying which jobs it takes on, where requests should be sent, and what permission a caller needs to have.
It means these helpers can find each other instead of being wired together by hand, much as a phone directory saves you from memorising numbers.