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Agent card

For every verified site, Sill publishes a signed, A2A-compatible agent card at its edge. The agent card is the canonical, machine-readable identity + capability statement for the site’s Sill surface.

Endpoint

Section titled “Endpoint”
GET https://edge.sill.so/v1/agent-card/{site_key}.json

The card is A2A-compatible: A2A’s discovery convention is the well-known path /.well-known/agent-card.json. Sill’s edge serves the per-site card at the URL above; you can publish the per-site URL anywhere an A2A client will accept a card location.

What it contains

Section titled “What it contains”
  • protocol_version: "a2a/1.2"
  • skills[]: the site’s exposed agent skills, in the A2A-conformant per-skill shape. The skill set is backing-filtered — only skills the site actually exposes through a wired backing appear here. No overclaim.
  • capabilities: A2A transport-flags object.
  • signing.algorithm: "ed25519".
  • signing.signing_key_id: the public key alias (matches the kid in the JWKS).
  • signing.issued_at / signing.expires_at: ISO-8601 UTC timestamps.
  • signing.envelope_signature: ed25519 signature over the JCS-canonical form of the card with envelope_signature removed (every other field, including the signing.* timestamps and key id, is bound by the signature).

Signing

Section titled “Signing”

The agent card is signed with an ed25519 key. The same public key is published in Sill’s JWKS as {kty: "OKP", crv: "Ed25519", alg: "EdDSA", use: "sig", kid: "foyer/edge/card-signing-v1"}. The kid in the JWKS matches the signing.signing_key_id on the card, so a verifier can resolve key → public bytes → verify in one step.

The JWKS endpoint:

GET https://edge.sill.so/.well-known/jwks.json

Any third party can fetch the JWKS and verify the agent card’s signature without any Sill-specific code. See Verify a signature.

Scope of claim

Section titled “Scope of claim”
  • The signed card advertises capabilities — it is a discovery surface, not a guarantee that every advertised skill is dispatchable today.
  • Transactional skill execution (money-movement skills) remains the Phase-2 mandate path. The card surface does not claim per-skill availability or SLA.
  • Sill claims no uptime SLA for this endpoint.

See also

Section titled “See also”