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.

2 hosts · 241 ms

HostCertsFirst seenLast seenDNS
syntr.io 18 2026-04-30 2026-09-21 ok
*.syntr.io 38 2026-03-26 2026-09-21 —

Programmatic access, with DNS A records: API GET /v1/hosts/syntr.io (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/syntr.io.