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RDAP is an HTTP-based protocol for registration-data lookups. For domain names, clients can use IANA bootstrap data to discover which RDAP service is authoritative for a TLD. RDAP is not DNS; it serves registration data rather than resolving hostnames.
What RDAP is for
RDAP stands for Registration Data Access Protocol. It defines HTTP-based services for querying registration data about objects such as domain names, nameservers and entities.
That makes it conceptually different from DNS. DNS answers questions required to resolve names. RDAP answers questions about registration data.
How bootstrap discovery works
A client needs to know which RDAP server to ask. IANA publishes bootstrap registries that map namespaces to the RDAP services responsible for them.
RDAP and WHOIS
WHOIS is the older registration-data query system. RDAP was standardized with structured responses, HTTP semantics and clearer mechanisms for internationalization and access control.
| Property | RDAP | WHOIS |
|---|---|---|
| Transport | HTTP / HTTPS | Traditionally TCP text service |
| Response shape | Structured JSON | Human-oriented text, format varies |
| Discovery | Standardized bootstrap registries | Historically varied |
How this site should use RDAP
A TLD reference page can safely show the RDAP base URL published through authoritative IANA data. It should not imply that the presence of an endpoint says anything about a domain's availability, price or registration policy.
Primary sources
These are the primary references this guide is designed around. When implementation data disagrees with editorial copy, the primary source wins.