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.

8 hosts · 309 ms

HostCertsFirst seenLast seenDNS
railboard.com 6 2026-05-03 2026-08-29 ok
link.railboard.com 6 2026-06-02 2026-09-26 ok
hello.railboard.com 4 2026-06-03 2026-09-25 ok
refunds.railboard.com 4 2026-04-09 2026-08-07 ok
receipts.railboard.com 5 2026-05-22 2026-09-19 ok
dev.railboard.com 6 2026-06-04 2026-09-27 ok
linkdev.railboard.com 6 2026-06-02 2026-09-27 ok
www.railboard.com 6 2026-04-14 2026-08-10 ok

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