Find every subdomain
of a domain.

Every hostname under a domain that ever appeared in a public TLS certificate — with certificate counts and first/last seen dates.

7 hosts · 149 ms

HostCertsFirst seenLast seen
staircase.co 19 2026-05-02 2026-10-01
admin.usdata.staircase.co 1 2025-06-18 2025-06-18
admin-dev.usdata.staircase.co 1 2025-06-18 2025-06-18
rate.staircase.co 1 2025-06-19 2025-06-19
register.staircase.co 1 2025-06-19 2025-06-19
client.staircase.co 1 2025-06-19 2025-06-19
www.staircase.co 21 2026-05-01 2026-09-29

Programmatic access: API GET /v1/hosts/staircase.co (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/staircase.co.