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.

23 hosts · 459 ms

HostCertsFirst seenLast seenDNS
theregister.com 22 2025-08-08 2026-09-02 ok
*.theregister.com 20 2025-08-08 2026-08-26 —
feed.theregister.com 5 2026-04-30 2026-10-06 nodata
old.theregister.com 3 2026-05-06 2026-08-20 ok
vendorvoice.theregister.com 4 2026-05-02 2026-07-08 ok
intelligence.theregister.com 3 2026-05-23 2026-09-05 ok
mobile.theregister.com 4 2026-05-04 2026-08-18 nodata
search.theregister.com 4 2026-04-27 2026-10-06 ok
gcp.search.theregister.com 2 2026-07-08 2026-08-31 ok
m.theregister.com 3 2026-05-04 2026-08-22 nodata
abm.theregister.com 1 2026-08-20 2026-08-20 ok
cdn.theregister.com 3 2026-05-05 2026-08-23 ok
go.theregister.com 3 2026-04-29 2026-08-19 ok
gcp.go.theregister.com 2 2026-07-08 2026-08-31 ok
nir.theregister.com 5 2026-04-29 2026-10-06 ok
preferences.theregister.com 1 2026-09-24 2026-09-24 ok
forums.theregister.com 4 2026-04-28 2026-10-06 ok
gcp.forums.theregister.com 2 2026-07-08 2026-09-01 ok
assets.theregister.com 2 2026-07-10 2026-09-05 ok
comments.theregister.com 4 2026-04-28 2026-08-14 nodata
tollbit.theregister.com 14 2026-04-19 2026-09-19 ok
comment.theregister.com 4 2026-04-30 2026-08-19 nodata
www.theregister.com 3 2026-05-03 2026-08-26 ok

Programmatic access, with DNS A records: API GET /v1/hosts/theregister.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/theregister.com.