What is WHOIS and RDAP?
WHOIS is a long-running protocol (originally defined in **RFC 3912**) for looking up domain registration data over a plain-text query. It returns who registered a domain, with which registrar, when, when it expires, and which name servers serve it. RDAP (Registration Data Access Protocol, **RFC 7480-7484**) is the modern successor: same data, but as structured JSON over HTTPS with consistent privacy redaction.
Most registries now respond with RDAP, with WHOIS preserved as a compatibility layer. Personal contact data is redacted under GDPR and ICANN's privacy specifications for most domains, but the operational fields — registrar, dates, name servers, status codes — remain public.
Why check WHOIS data?
1Domain age affects deliverability
Brand-new domains are treated as suspicious by mailbox providers — confirm age before launching a campaign
2Catch expiry before it bites
An expired domain takes everything with it — mail, sites, certificates — monitor the expiry date proactively
3Verify a domain hasn't changed hands
WHOIS updates reveal registrar transfers and ownership changes that may signal trouble
4Audit operational status codes
Codes like `pendingDelete` or `clientHold` warn that the domain is on its way out — act before it disappears
How a WHOIS / RDAP lookup works
You submit a domain to the checker.
The checker first tries RDAP — it asks IANA's bootstrap service which RDAP server is authoritative for the TLD.
It queries that RDAP server over HTTPS and parses the structured JSON response.
If RDAP is unavailable, it falls back to the legacy WHOIS protocol on TCP port 43.
Registrar, creation / update / expiry dates, name servers, and status codes are extracted and normalised — contact data is omitted to respect privacy redaction.
Sample WHOIS query
whois example.com
# or with RDAP via curl
curl https://rdap.org/domain/example.com | jq .Common WHOIS fields
registrar— company that registered the domaincreated— first registration dateupdated— last change to the WHOIS recordexpires— current registration end datename servers— authoritative DNS serversstatus codes— operational flags set by registrar / registryCommon WHOIS issues and fixes
Domain in `redemptionPeriod`
Registration lapsed but is still recoverable — pay your registrar's restore fee immediately
Expiry under 30 days
Renew now to avoid losing mail flow, certificates, and search reputation
Registrar transfer locked
`clientTransferProhibited` is a good security setting — unlock only when initiating a planned transfer
Contact data missing
GDPR redaction hides registrant data — operational fields remain public, which is what matters for deliverability
よくある質問 (FAQ)
WHOIS is a long-running protocol for looking up domain registration data: who registered it, when, with which registrar, and when it expires. RDAP (Registration Data Access Protocol) is its modern successor — same data, but returned as structured JSON over HTTPS with consistent privacy redaction. Most registries now return RDAP; the checker shows whichever source was used.
Mailbox providers and anti-spam services weight domain age heavily — brand-new domains are treated as suspicious by default. Confirming your domain's registration age, registrar, and that the WHOIS data isn't about to expire is part of pre-warmup hygiene and explains many cold-start deliverability problems.
It is the number of days until the registration lapses. Once a domain expires it enters a redemption grace period, and after that it can be reclaimed by anyone — including spammers who buy expired domains to abuse their residual reputation. Renew well before expiry and treat a value below 30 as urgent.
GDPR and ICANN's temporary specification require registrars to redact personal contact data for most domains. The checker still shows the registrar, registration and expiry dates, name servers, and status codes — all of which are public — but the registrant's name, email, and phone are usually hidden behind a privacy proxy.
Status codes describe operational restrictions on the domain. 'clientTransferProhibited' means the registrar has blocked transfers to another registrar — usually a good security setting. Codes prefixed with 'server' are set by the registry itself. Codes like 'pendingDelete' or 'redemptionPeriod' warn that the domain is on its way to deletion.
Almost. Public WHOIS / RDAP works for every generic TLD (.com, .net, .io, etc.) and most country-code TLDs. A few country registries publish minimal data — only registrar and expiry — and some restrict programmatic lookups. The checker handles those gracefully and reports whichever fields were available.