GlossaryThe domain name
RDAP
Definition
RDAP, the Registration Data Access Protocol, is the protocol that replaces WHOIS for looking up a domain name's registration data. It returns a structured JSON answer over HTTPS, with field names that are the same at every registry.
Why it matters when you monitor domains
WHOIS gave you text to interpret: every registry laid out its lines its own way, and any program reading them broke the first time a layout changed. RDAP gives you an object where the expiry date is always called expiration, whichever registry you are talking to. That is what makes it possible to track hundreds of domains without rewriting your parser every six months.
It is how DomainVigil reads an expiry date: the registry's own RDAP server where IANA publishes one, an RDAP aggregator otherwise. The other difference is invisible but real — the answer is encrypted, and a registry can return more of it to an identified requester than to an anonymous one, which WHOIS could never do.
The same domain, seen through RDAP
Dates are no longer lines of text to slice apart; they are named events.
{
"objectClassName": "domain",
"ldhName": "example.com",
"status": ["client transfer prohibited"],
"events": [
{ "eventAction": "registration", "eventDate": "2015-03-14T09:12:00Z" },
{ "eventAction": "expiration", "eventDate": "2027-03-14T09:12:00Z" }
],
"nameservers": [{ "ldhName": "ns1.example.net" }]
}Status codes are spelled out in separate words here — “client transfer prohibited” — where WHOIS runs them together. The field names, though, do not move from one registry to the next, and that is the whole point.
The usual mistake
Leaving a monitoring job pointed at text-based WHOIS, and watching it go quiet the day a registry switches its service off. Nothing raises an alarm: the tool gets an empty answer and concludes there is nothing to report.
How to avoid it: Query RDAP first, and keep WHOIS as a fallback only for the ccTLDs that have not moved over yet. And above all, treat “I could not find out” as a state you display, never as a green light.
Source: The protocol is defined by a series of IETF standards, including RFC 9082 and RFC 9083 for queries and responses. ICANN set 28 January 2025 as the end of the WHOIS service requirement for generic extensions, apart from .com, .name and .post.
Related terms
Where to go next
Knowing the words is half the job
The other half is knowing which of your domains is about to become a problem. DomainVigil watches expiry, DNS, certificates and reputation, and tells you before your client does.
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