TLD Lookup

Check whether a domain extension supports RDAP or WHOIS lookups, and find its registry information.

Enter a bare extension (e.g. io) or a full domain — either works.

What is a TLD lookup?

A TLD lookup checks a top-level domain, the part after the last dot such as .com, .io or .de, and tells you how its registration data can be looked up. Not every extension works the same way: some publish data through the modern RDAP protocol, some only through classic WHOIS, and a few through neither.

Knowing this in advance saves time. It explains why a lookup for one extension shows rich, structured data while another shows less, or nothing at all.

How the TLD lookup works

The tool checks two official sources run by IANA, the organisation that coordinates the root of the domain name system. First, the RDAP bootstrap registry, a published file that lists which top-level domains have an RDAP service and where it lives. Second, the IANA WHOIS service, which refers each extension to the WHOIS server operated by its registry.

The result shows whether RDAP is supported, with the server address, and whether a WHOIS referral exists. Both answers reflect the current published data rather than a fixed list.

How to use the TLD lookup

  1. Enter a bare extension such as io, or a full domain such as example.io; both work.
  2. Run the lookup.
  3. Check "RDAP supported" to see whether structured lookups are available for that extension.
  4. Check "WHOIS referral available" to see whether a classic WHOIS server is listed.

What the TLD lookup results mean

RDAP supported

The extension appears in the IANA bootstrap registry, so our WHOIS Lookup and RDAP Lookup can return structured data for its domains. All generic top-level domains are required to offer RDAP; many country-code domains have added it too.

WHOIS referral available

IANA lists a WHOIS server for the extension. Our tools use it as a fallback when RDAP is not available.

Neither available

The registry offers no public lookup path we can use. Domains under that extension can still exist and work normally; you will need the registry's own website to look them up.

Generic and country-code domains

Generic top-level domains (gTLDs) such as .com, .org and newer ones like .shop operate under ICANN contracts, which require RDAP. Country-code domains (ccTLDs) such as .uk, .de or .jp are run by national registries under their own rules, so their lookup services and privacy policies vary widely.

Why some domain extensions behave differently

Each top-level domain is run by its own registry, and each registry sets its own rules. Some country-code registries only accept registrations from people or businesses with a local address. Some publish very little registration data, especially about individuals, for privacy reasons. Others run their own WHOIS servers with a unique format. Knowing how an extension can be looked up explains why one domain returns a detailed record while another returns only a few fields.

The lookup method also affects our other tools. Domain age, expiry and availability checks all rely on the same registration data, so an extension with neither RDAP nor WHOIS will give limited results everywhere.

Common uses

  • Understanding why a WHOIS result for a domain looks limited.
  • Checking an extension before building software that relies on RDAP.
  • Researching a new or unfamiliar extension before registering a domain under it.

Common problems and fixes

The extension is not recognised. Check the spelling and leave out the dot; for example enter co.uk or uk rather than a misspelled ending.

RDAP says no, but I expected yes. Support is read from the live bootstrap file. Some registries add RDAP later than others, so check again after a while.

Related tools

Frequently asked questions

What is a TLD?

TLD stands for top-level domain, the last part of a domain name after the final dot, such as .com, .org, .io or .de. Each TLD is run by a registry that keeps the records for every domain under it. There are generic TLDs and country-code TLDs, and each follows its own registration rules.

What is the difference between a gTLD and a ccTLD?

A gTLD is a generic top-level domain such as .com, .net or .shop, operated under contracts with ICANN. A ccTLD is a two-letter country-code domain such as .uk, .fr or .jp, run by a national registry under local policies. That is why lookup services and privacy rules vary more among ccTLDs.

How do I know if an extension supports RDAP?

Enter the extension in this TLD lookup. It checks the IANA RDAP bootstrap registry, the official list of extensions that have an RDAP service and where that service is located. If the extension is listed, structured RDAP lookups are available for its domains.

Why does WHOIS not work for some country-code domains?

Country-code registries decide for themselves whether to offer public lookups. Some only provide a search form on their own website, some restrict access, and a few offer no public service at all. When neither RDAP nor a WHOIS referral is available, our lookup tools cannot query that extension.

Can I enter a full domain in the TLD lookup?

Yes. You can enter a bare extension such as io or a full domain such as example.io. The tool works out the extension and checks it, so you can paste a domain straight from the address bar without trimming it first.

What is IANA?

IANA, the Internet Assigned Numbers Authority, coordinates key internet registries, including the root zone of the domain name system. It publishes which registry runs each top-level domain, the RDAP bootstrap file and a WHOIS service that points to each registry's own WHOIS server.

Are all generic domain extensions required to support RDAP?

Yes. ICANN's agreements require generic top-level domain registries and accredited registrars to provide RDAP, and since January 2025 RDAP has been the official source of their registration data. Country-code domains are run under national rules rather than these agreements, so whether they offer RDAP, WHOIS or neither varies from one extension to the next.