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WHOIS vs RDAP: where the data comes from

Every domain lookup tool — including ours — gets its data from one of two public protocols: the venerable WHOIS and its modern replacement, RDAP. Knowing the difference helps you judge how much to trust what any checker tells you.

WHOIS: 1982 calling

WHOIS is a plain-text protocol from the early internet: you open a connection to a registry server on port 43, send a domain name, and get back free-form text. Every registry formats that text differently — "Registry Expiry Date", "Expiry date", "paid-till", "renewal date" all mean the same thing at different registries. Tools have to parse these formats with pattern-matching, which is where lookup errors usually creep in.

RDAP: the structured successor

RDAP (Registration Data Access Protocol) was standardised in 2015 and has been mandatory for all gTLDs since 2019. In January 2025, ICANN formally retired the WHOIS port-43 requirement for gTLDs — RDAP is now the authoritative source. It's a simple HTTPS+JSON API:

• Dates come as proper machine-readable timestamps — no parsing guesswork.
• Status codes (like redemptionPeriod) come as a clean list.
• IANA publishes a "bootstrap" registry mapping every TLD to its official RDAP server, so a tool always knows where to ask.
• A 404 response means, authoritatively, "this domain is not registered".

What about country-code domains?

ccTLDs aren't bound by ICANN's RDAP mandate, but many have adopted it anyway — Nominet (.uk), AFNIC (.fr), SWITCH (.ch), DENIC (.de) and others run RDAP servers. The stragglers still answer on classic WHOIS, which is why a good checker speaks both.

How our checker uses them

When you check a domain, we:

• Look up the TLD's official RDAP server in the IANA bootstrap file and query it first.
• Fall back to port-43 WHOIS (following registrar referrals) if the TLD has no RDAP coverage.
• Normalise the result — expiry date, status codes, registrar — and run it through our lifecycle model to estimate the actual drop date.