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.

4 hosts · 239 ms

HostCertsFirst seenLast seen
guideline.com 3 2025-08-04 2026-07-14
*.guideline.com 3 2025-08-04 2026-07-14
email1.guideline.com 3 2026-04-14 2026-06-13
image.email.guideline.com 2 2026-01-21 2026-01-21

Programmatic access: API GET /v1/hosts/guideline.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/guideline.com.