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 · 293 ms

HostCertsFirst seenLast seenDNS
mta-sts.serko.co.nz 2 2026-10-01 2026-10-01 ok

Programmatic access, with DNS A records: API GET /v1/hosts/serko.co.nz (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/serko.co.nz.