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.

6 hosts · 261 ms

HostCertsFirst seenLast seenDNS
runsystem.net 26 2025-10-28 2026-09-19 ok
*.runsystem.net 21 2025-10-28 2026-09-19 —
we20.runsystem.net 9 2026-05-29 2026-09-25 ok
bpo.runsystem.net 11 2026-06-04 2026-08-30 ok
mail.bct.runsystem.net 3 2026-06-19 2026-09-01 ok
testnew.runsystem.net 5 2026-05-03 2026-08-29 ok

Programmatic access, with DNS A records: API GET /v1/hosts/runsystem.net (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/runsystem.net.