Whois is a lookup system used to retrieve registration information about a domain name. Depending on the extension and privacy rules, it can show registrar, dates, nameservers, status and sometimes contact details.
Today many registries also use RDAP, a modern protocol designed to provide structured registration data. Privacy regulations may limit the personal information displayed publicly.
This guide explains what Whois is, how to use it from websites or command line tools, how privacy works and how historical Whois can help evaluate a domain.