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 · 264 ms

HostCertsFirst seenLast seenDNS
protectsystems.com 5 2026-04-16 2026-09-03 ok
mta-sts.protectsystems.com 1 2026-05-23 2026-05-23 ok
www.protectsystems.com 5 2026-04-16 2026-09-03 ok
pay.protectsystems.com 2 2026-04-16 2026-06-16 ok
www.pay.protectsystems.com 2 2026-04-16 2026-06-16 nxdomain

Programmatic access, with DNS A records: API GET /v1/hosts/protectsystems.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/protectsystems.com.