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.

14 hosts · 409 ms

Download CSV
HostCertsFirst seenLast seen
rfm.io 8 2026-05-09 2026-09-04
b.rfm.io 2 2026-10-03 2026-10-03
app.staging.rfm.io 1 2026-06-17 2026-06-17
waybook.rfm.io 5 2026-05-18 2026-09-16
app.rfm.io 2 2026-02-15 2026-07-08
mta-sts.rfm.io 5 2026-05-08 2026-09-03
chat.rfm.io 1 2026-09-03 2026-09-03
app.uat.rfm.io 1 2026-06-17 2026-06-17
support.rfm.io 3 2025-09-12 2026-07-24
trust.rfm.io 3 2025-09-09 2026-07-21
app.dev.rfm.io 1 2026-06-17 2026-06-17
www.rfm.io 10 2026-05-08 2026-09-04
notify.www.rfm.io 1 2026-05-26 2026-05-26
*.notify.www.rfm.io 1 2026-05-26 2026-05-26

Programmatic access: API GET /v1/hosts/rfm.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/rfm.io.