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.

2 hosts · 217 ms

HostCertsFirst seenLast seen
email.cats.org.uk 26 2026-04-22 2026-10-03
*.email.cats.org.uk 13 2026-06-04 2026-10-03

Programmatic access: API GET /v1/hosts/email.cats.org.uk (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/email.cats.org.uk.