WHOIS is a query and response protocol used to retrieve information about registered Internet resources such as domain names, IP address blocks, and autonomous systems. It allows users to query databases that store details about the registered users or assignees of these resources, providing data in a human-readable format
. The WHOIS protocol operates over TCP, typically using port 43, where a client sends a query (usually a domain name) to a WHOIS server and receives registration information in response. This includes registrant contact details, administrative and technical contacts, registration and expiration dates, and name servers
. The WHOIS database is maintained to provide transparency about domain ownership and is commonly used for domain registration verification, contacting domain owners, legal investigations, network troubleshooting, and market research. However, privacy protection services offered by registrars can mask some registrant details to protect privacy
. WHOIS originated in the early 1970s with the ARPANET Network Information Center and was standardized in the 1980s. It remains a fundamental tool for managing and researching Internet domain registrations
. Several online services and tools, such as who.is, Whois.com, DomainTools, GoDaddy WHOIS, Namecheap Whois, and ICANN Lookup, provide user-friendly interfaces to perform WHOIS lookups and access domain registration data
