Find every subdomain
of a domain.

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

1 host · 176 ms

HostCertsFirst seenLast seen
mta-sts.sophos.hk 6 2026-06-03 2026-10-01

Programmatic access: API GET /v1/hosts/sophos.hk (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/sophos.hk.