RDAP, WHOIS or DNS: which answer to trust

RDAP asks the registry directly

RDAP is the successor to WHOIS and behaves like a public API: you ask about one name and get either its registration record or a plain statement that no such domain exists. The answer comes from the database that registration itself runs on, so it is binding.

This is the best result available anywhere. The catch is that not every registry runs the service.

Only 70 of 248 country registries offer it

We checked the IANA bootstrap file, the official directory of RDAP servers: of 248 country-code extensions, 70 have an entry and 66 actually answer. The rest of the world offers nothing comparable.

RDAP is available for .pl, .uk, .fr, .nl, .cz, .no, .fi, .ca, .au, .br, .ua and every large generic extension including .com, .net, .org and .info. It is missing for .de, .eu, .it, .es, .ch, .at, .se, .dk, .io, .co and .me — which happen to be among the most asked-about names in Europe.

WHOIS still works, awkwardly

Several registries without RDAP publish a classic WHOIS service. The answer can be just as reliable, but every registry formats it differently, many rate-limit requests and some redact the data entirely. Checking at scale is painful.

DNS is the fallback, and it guesses

When neither service exists, the only remaining question is whether the name has name servers. If it does, the domain is certainly taken.

The reverse is not safe. A domain someone registered and never used has no name servers and looks exactly like a free one. That is why a DNS-based result should read as probably available rather than available.

What this means in practice

For .pl, .com or .uk you can treat the answer as final and plan around it. For .de, .eu or .io, treat it as a strong hint and confirm with a registrar before you print anything.

The only fully authoritative moment is when a registration request reaches the registry. Everything before that is a photograph of a moment that has already passed.