An A2A Agent Card published at /.well-known/agent-card.json is how one agent discovers another's identity, skills, and capabilities — and it's the layer AP2 and x402 ride on. This tool validates the card against the A2A v1.0 shape, checks the signed-card signatures block, and confirms an AP2 / x402 extension is declared correctly. Produces a §4 compliance_control OpenChainGraph artifact.
/.well-known/agent-card.json. An example is pre-loaded; the second button loads a signed card.