Find every subdomain
of a domain.

Every hostname under a domain that ever appeared in a public TLS certificate — with certificate counts, first/last seen and live DNS status.

1 host · 368 ms

HostCertsFirst seenLast seenDNS
hello.synthesiahq.com 3 2026-04-15 2026-04-29 nodata

Programmatic access, with DNS A records: API GET /v1/hosts/synthesiahq.com (API key for paging).

Shown here: hostnames with a certificate that is valid now or expired within the last 90 days. The full history since 2013 — hostnames whose last certificate expired earlier — is a Pro plan method: GET /v1/hosts-history/synthesiahq.com.