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.

5 hosts · 258 ms

HostCertsFirst seenLast seenDNS
helsing.ai 5 2026-04-22 2026-08-25 ok
blog.helsing.ai 5 2026-05-05 2026-09-03 ok
developer.helsing.ai 5 2026-05-11 2026-09-10 ok
mta-sts.helsing.ai 2 2026-02-03 2026-06-20 ok
www.helsing.ai 4 2026-04-20 2026-08-21 ok

Programmatic access, with DNS A records: API GET /v1/hosts/helsing.ai (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/helsing.ai.