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.

4 hosts · 235 ms

HostCertsFirst seenLast seenDNS
21tech.io 2 2025-07-14 2026-06-14 nodata
*.21tech.io 2 2025-07-14 2026-06-14 —
qa.21tech.io 1 2025-07-14 2025-07-14 nodata
*.qa.21tech.io 1 2025-07-14 2025-07-14 —

Programmatic access, with DNS A records: API GET /v1/hosts/21tech.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/21tech.io.