What Is RDAP and How Do You Look Up a Domain, IP Address, or ASN?

Updated

RDAP (Registration Data Access Protocol) is the structured, HTTPS-based replacement for WHOIS. You use it to look up registration data for a domain name, an IP address or CIDR block, or an Autonomous System Number (ASN), and you get back a JSON record instead of free-form text. A private RDAP lookup tool such as client.rdap.org sends your query directly from your browser to the relevant registry's RDAP server over an encrypted HTTPS connection, so only that registry sees the query.

What RDAP is and why it replaces WHOIS

WHOIS returns unstructured text that varies by registry, which makes it hard to parse reliably and hard to extend. RDAP standardizes both the transport and the data model:

  • Transport: HTTPS requests instead of a plain-text protocol on port 43.
  • Format: JSON with defined fields, so responses can be parsed and validated programmatically.
  • Access control: Because responses are structured, registries can return different levels of detail depending on who is asking, rather than exposing everything to everyone.

The practical effect for you: the same query type returns a consistent shape of answer across registries that support RDAP.

How RDAP differs from WHOIS

Dimension WHOIS RDAP
Protocol Plain text, typically port 43 HTTPS
Output Free-form text, varies by registry JSON with defined fields
Parsing Fragile, registry-specific Structured and machine-readable
Access control Limited, largely uniform exposure Can vary detail by requester
Coverage Broad, long-established All generic TLDs; only some ccTLDs so far

The coverage gap matters in practice. All generic TLDs now support RDAP, but only a few country-code TLDs (ccTLDs) have deployed it. If a ccTLD has not deployed RDAP, an RDAP lookup for that domain will not return a registry record.

What you can look up

An RDAP lookup tool supports several query types:

  • Domain — registration data for a domain name.
  • TLD — information about a top-level domain.
  • IP / CIDR — allocation data for an IP address or a CIDR block.
  • AS Number — data for an Autonomous System Number.
  • Entity — a registered entity such as a contact or organization handle.
  • Registrar — registrar records.

Note one structural limitation: there is currently no bootstrap registry for ICANN-accredited registrars, so registrar queries are sent to the registrars.rdap.org server rather than resolved through a bootstrap mechanism.

How to run a lookup and read the response

  1. Choose the query type that matches what you have — domain, IP/CIDR, ASN, entity, or registrar.
  2. Enter the value and submit. Your browser connects directly to the registry's RDAP server over HTTPS.
  3. Read the JSON response. The record contains the registration data for that object, with fields defined by the RDAP data model.
  4. Decide whether to follow the referral. If the "Follow referral to registrar's RDAP record" checkbox is checked, the sponsoring registrar may also see your query — but only if the registry provides a referral.

The privacy point is the reason to care about step 4. With the referral option off, only the relevant registry sees your query. Turning it on can add the registrar as a second party that sees it. If you want the narrowest exposure, leave the referral option unchecked and accept that you may not see the registrar's portion of the record.

When a lookup fails or looks wrong

Two distinct problems come up:

  • No RDAP record for a ccTLD. This is a coverage issue, not an error in your query. The ccTLD has not deployed RDAP, so there is no registry RDAP server to answer. There is no RDAP equivalent to fall back on for that TLD.
  • A response that looks incorrect. RDAP responses are the registry's or registrar's content. If something in the response is wrong, contact the relevant registry or registrar — the lookup tool is only relaying the query. To check whether a response is malformed rather than merely unexpected, you can run it through an RDAP Validator.

Quick reference

  • RDAP = structured, HTTPS, JSON replacement for WHOIS.
  • Supported queries: domain, TLD, IP/CIDR, ASN, entity, registrar.
  • Privacy: your browser connects directly to the registry over HTTPS; only the registry sees the query unless you follow the referral to the registrar.
  • Coverage: all generic TLDs support RDAP; only some ccTLDs do.
  • Registrar queries: no bootstrap registry exists, so they go to registrars.rdap.org.
  • Bad response content: report it to the registry or registrar, and validate it with an RDAP Validator first.