Many websites allow Whois or RDAP lookups directly from a browser. They are useful when you need a quick check without installing command line tools.
Registrar websites, registry websites and independent domain tools can show registration dates, expiration dates, nameservers, status codes and sometimes historical or SEO-related data.
For official information, prefer the registry or registrar source. Third-party tools can be convenient, but they may cache data or combine information from multiple sources.
When evaluating a domain for purchase, use more than one source: Whois or RDAP, DNS checks, archived snapshots, backlink tools and marketplace history all help build a more complete picture.