Whois

WHOIS is a query-and-response protocol used for querying databases that store registered users or assignees of Internet resources, such as domain names, IP address blocks, and autonomous systems. It is widely used by network operators, registrars, law enforcement, security researchers, and system administrators to obtain contact information and status data about a resource.

A client sends a text query to a WHOIS server (traditionally on TCP port 43). The server responds with a human-readable record containing fields such as the registrant or organization name, administrative and technical contact details, the registrar, the creation and expiration dates, domain status, and the authoritative name servers.

In practice, there are separate WHOIS services for domain names and for IP addresses. Domain WHOIS records are maintained by registries and registrars; many top-level domains use registries managed under ICANN frameworks. The information provided can vary by TLD and jurisdiction, and may be subject to privacy controls.

Privacy and policy: The EU General Data Protection Regulation and other privacy laws have led many registries to redact or limit personal data or to rely on privacy or proxy services. In response, RDAP (Registration Data Access Protocol) has emerged as a modern alternative, offering structured data and access controls, but adoption is uneven.

Limitations: Data accuracy depends on the registrant-provided information; records are not always up to date. Not all registries publish complete data, and some use rate limiting or blocking. Privacy measures have reduced public visibility of personal details in some cases.