What is WHOIS, and why does it matter?
WHOIS is the public record system for domain names — it tells you who registered a domain, when it was created and when it expires, and which registrar and name servers it uses. It's the first thing to check before trying to register, buy, or transfer any domain.
Available vs. taken. A clean WHOIS lookup for an available domain usually returns a clear "no match" response. A registered domain returns full record details instead — though exactly how much is public depends on the registry and any privacy protection in place.
Why results can vary. Different registries run their own WHOIS servers with their own response formats, and some enforce strict rate limits or block automated lookups outright. That's why a reliable checker cross-references multiple sources (RDAP, WHOIS, and registrar-level lookups) rather than trusting a single server's raw text — a premium or reserved domain, for example, can return wording that looks like "available" at a glance but isn't.