How DomainFinch Checks Domain Availability

The short version

When you type a name into DomainFinch, your browser asks public DNS resolvers whether the domain has nameservers. If the answer is NXDOMAIN (the domain does not exist in DNS), the name is probably unregistered. Your browser then asks the official registry for that extension, using the Registration Data Access Protocol (RDAP), for the domain's registration record. A 404 Not Found confirms the name is not registered; a 200 OK means it is registered, and the response tells us the registrar, the key dates and the nameservers.

There is no DomainFinch backend in that loop. We do not proxy, log or store your queries, and we never see the names you check.

Step 1: a fast DNS lookup

DNS is the internet's address book. Every registered domain that is in use is "delegated" by its registry, meaning the registry's zone points to nameservers for it. We look for those nameservers using DNS-over-HTTPS (DoH), which lets a web page make DNS queries over an ordinary encrypted HTTPS connection.

• Primary resolver: Cloudflare's public 1.1.1.1 resolver, via its JSON API.
• Fallback resolver: Google Public DNS, used automatically if the first request fails or times out.

For each domain we request its NS (nameserver) records and read the response code:

DNS is extremely fast and is cached all over the world, which is what makes it possible to check a dozen extensions while you are still typing. It is also an indirect signal: DNS tells us whether a name is delegated, not whether it is registered. That distinction is why there is a second step.

Step 2: confirming with RDAP

RDAP is the modern, standardised replacement for the old WHOIS protocol. It returns structured JSON over HTTPS, and ICANN requires generic top-level domain registries and registrars to support it. Many country-code registries offer it too.

To know which server to ask, we read the IANA RDAP bootstrap file, a public registry published by IANA that maps each top-level domain to its RDAP service. For a .com name, for example, the bootstrap points to Verisign's RDAP server. Your browser then requests the domain record directly from that server:

• HTTP 404: the registry has no record. The domain is not registered, and we mark it available.
• HTTP 200: the domain is registered. We display the registrar, creation, last-updated and expiry dates, status codes and nameservers. The same data powers our WHOIS lookup.
• Rate limit or error: we fall back to the DNS result and label it "likely", so you know it has not been confirmed.

Accuracy limits you should know about

No free availability checker is perfect, and we would rather tell you where ours can be wrong than overstate it. The final word always belongs to the registrar at checkout.

Premium and reserved names

Registries hold back some names as reserved (for example, certain short strings or names blocked by policy) and sell others as premium at a higher price. These names are often unregistered, so DNS returns NXDOMAIN and RDAP returns 404, yet you cannot buy them at the standard price, or at all. When a registrar quotes a premium price, it is the registrar's quote that counts.

Registries without browser-accessible RDAP

Some extensions, mostly country codes, do not publish an RDAP server in the IANA bootstrap file, or publish one that does not allow requests from web pages (a browser security feature called CORS). For those extensions we can only use DNS, and we label results as "likely available" rather than confirmed.

Registered but not delegated

A small number of domains are registered but have no nameservers, for instance names on hold, suspended for a dispute, or registered and never configured. DNS says NXDOMAIN for these even though they are taken. This is rare, but it is exactly the case that a DNS-only checker gets wrong, and it is the main reason we confirm every DNS "available" result with RDAP whenever the registry allows it.

Timing

Registrations, deletions and drops happen continuously. A name that was available a minute ago can be registered by someone else, and recently deleted names may still be cached by resolvers for a short time. If a name matters to you, register it rather than leaving it in a tab.

Privacy: why we never store searches

Domain searches are sensitive. A list of names someone is checking can reveal an unannounced product, a company rebrand or an acquisition. There is also a long-standing worry in the domain industry about front-running: the suspicion that names people search for get registered by someone else shortly afterwards, so they can be resold. Whatever the truth of any specific case, the safest design is one where the search data never exists in the first place.

That is how DomainFinch is built:

• No backend for searches. Lookups go straight from your browser to the public resolvers and registry RDAP servers. We have no server that receives the names.
• No accounts. You never need to sign up or give us an email address.
• Local shortlist. Names you save are kept in your browser's localStorage on your device. Clearing your browser data removes them.
• No search terms in analytics. We do not record what you type.

Two honest caveats. First, the DNS resolvers and registries you query necessarily see the requests, just as they do for any normal web browsing; Cloudflare and Google publish their own privacy policies for their public resolvers. Second, if you click a registrar link to buy a name, the name is passed to that registrar so it can show you the price, which is the point of the click.

How we make money

DomainFinch is free. It is funded by affiliate links to registrars and hosting providers, and by advertising. Affiliate commissions never change availability results: the checker reports what DNS and RDAP say, regardless of where you choose to buy. See our editorial policy for how we keep recommendations independent.

For developers and journalists

You are welcome to link to this page as a description of the method. The building blocks are all public: DNS-over-HTTPS JSON APIs from Cloudflare and Google, the IANA RDAP bootstrap registry for domain names, and the RDAP standards published by the IETF. If you find a case where DomainFinch reports the wrong result, please tell us; reproducible reports are how we improve the edge cases above.

FAQ