The Registration Data Access Protocol (RDAP) is the successor to WHOIS, standardized by the IETF (RFC 7480-7484 and later updates). It returns domain, IP and ASN registration data as structured JSON over HTTPS.
Advantages over WHOIS include consistent machine-readable output, standardized error codes, internationalization support, a bootstrap system that finds the correct server for any TLD automatically, and the ability to offer differentiated access (for example, more data to authenticated, authorized requesters).
ICANN requires gTLD registries and registrars to run RDAP services, and it became the definitive source for gTLD registration data in 2025. Tools like DomainFinch can use RDAP to check whether a domain is registered.
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Related terms
- DNS (Domain Name System)
- DNS is the internet's distributed directory that translates domain names into IP addresses and other records so browsers and mail servers can connect.
- Nameserver
- A nameserver is a DNS server that holds and answers queries for a domain's records; you set which nameservers are authoritative at your registrar.
- A record
- An A record is a DNS record that maps a domain or subdomain to an IPv4 address, telling browsers which server hosts the site.
- CNAME record
- A CNAME record makes one hostname an alias of another, such as www.example.com pointing to example.com or to a hosting provider's hostname.