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 · 193 ms

HostCertsFirst seenLast seen
mta-sts.mail.rmu.edu 2 2026-02-18 2026-07-09

Programmatic access: API GET /v1/hosts/mail.rmu.edu (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/mail.rmu.edu.