What is an A2A agent card?
An A2A agent card is a JSON document that describes an AI agent built on the Agent2Agent (A2A) protocol: its name, what it can do, the URL to reach it and how to authenticate, so other agents can find it and hand it work. The A2A specification puts it at https://{your-domain}/.well-known/agent-card.json.
From our data: As of 3 Nov 2026, 7 of the 214 software vendors in our rankings publish an A2A agent card, against 90 that run a remote MCP server.
Who needs one
Only sites that run an agent other agents should talk to, like a support agent, a booking agent or a procurement agent. If what you offer is data and actions rather than an agent, an MCP server or an API with an OpenAPI spec is the better fit, and most of the vendors we scan choose that.
A2A vs MCP
MCP connects an agent to tools and data: your product becomes a set of tools a model can call. A2A connects agents to each other: your agent takes a task from someone else's agent and works on it, possibly for a while, then reports back. They're complementary, and both now sit under the Linux Foundation.
Publishing one
Serve it at /.well-known/agent-card.json
Return JSON with a 200. Some early implementations used /.well-known/agent.json; current versions of the spec use agent-card.json.
Describe skills plainly
Each skill gets a name, a description and examples. A calling agent decides whether to use yours from those words.
Declare auth
Say which security schemes the agent accepts, so a caller knows how to get a token before it tries.
Sign it if it matters
The spec allows signed cards, so callers can verify the card really came from you.
Check it yourself
You should get JSON describing the agent. An HTML page or a 404 means there's no card at the standard path.
curl -s https://example.com/.well-known/agent-card.json | head -c 600
Questions
Is agent.json the same as agent-card.json?
They're the same idea at different paths. Early A2A implementations used /.well-known/agent.json; the current specification uses /.well-known/agent-card.json. Our scanner checks both.
Do I need an agent card to be found by ChatGPT or Claude?
No. Assistants find you through search and your web pages. An agent card is for agent-to-agent calls.
Should I build A2A or MCP first?
For most products, MCP: it puts your actions inside the assistants people already use. Add A2A when you have an agent of your own that other agents should delegate to.