How the registry lookup works
Every top-level domain is run by a registry that keeps the authoritative list of registered names. RDAP, the Registration Data Access Protocol (RFC 9082 and RFC 9083), is the HTTPS and JSON successor to WHOIS, and gTLD registries have been required to offer it since 2019. IANA publishes a bootstrap file that maps each TLD to its registry's RDAP server, and the tool reads that file to know where to ask.
The query is a plain request for the domain object, for example /domain/mybrand.dev on the registry's server. An HTTP 404 means the registry has no such name, and the card reads Available. A 200 response carries the registration record, from which the tool takes the registrar name and the expiration event. Up to six registries are queried at a time, each with a timeout of a few seconds.
What happens when the registry cannot answer
Some registries, mostly country-code ones that are not bound by ICANN contracts, publish no RDAP server, and any server can be slow or refuse a burst of queries. In those cases the tool falls back to DNS and asks public resolvers for the domain's NS records. A delegated name is certainly registered, so the card reads Registered, without registrar or expiry lines because DNS does not carry them.
If DNS says the name does not exist, the card reads Unconfirmed with a note that it is probably available. The hedge is deliberate. Registries publish a delegation only for names that have nameservers, so a domain that is registered but has none, or is on hold, is invisible in DNS. If neither the registry nor DNS gave a usable answer, the note says the registry could not be reached.
Reading the cards
A keyword search adds a line above the grid saying how many of the 12 extensions appear to be available. Available cards have a green border and a note reminding you to confirm at a registrar. Registered cards list Registrar and Expires when the registry returned them, plus a View WHOIS link that opens WHOIS Lookup for the same name.
Keywords may contain letters, digits and hyphens, cannot start or end with a hyphen and are limited to 63 characters, the DNS limit for one label. A name with accents or non-Latin script has to be entered in its xn-- form, which Punycode Converter produces. Entering a full domain checks only that name, and it can use an extension outside the list of 12.
Why an available name may still be out of reach
Registries keep some unregistered names for themselves. Reserved names cannot be bought at all, and premium names carry a price set by the registry that can be many times the standard fee. Both can come back as not found in a lookup. Only a registrar's checkout shows the real price and whether the order will go through.
Timing matters too. Availability is a snapshot, and a name that is free now can be registered a minute later by someone else. Nothing here reserves a name for you. If it is the name you want and the registrar confirms it, register it then instead of coming back next week.
Taken names, expiry dates and drops
An expiry date is not a release date. For gTLDs, a domain that is not renewed usually stays with its registrar through an auto-renew grace period of up to 45 days, then spends 30 days in redemption, when only the previous owner can restore it, and five days in pending delete before the registry releases it. Sought-after names are often caught by backorder services the moment they drop.
If the name you want is taken, find out whether it is in use before planning around it. DNS Lookup shows whether it has address and mail records, and the WHOIS record shows when it was created and through which registrar. A long-held, actively used domain is unlikely to lapse, so a different name or extension is the practical route.