Whois

WHOIS is the traditional name of a service and protocol used to query information associated with domain names and Internet resources. The name is pronounced “who is” and is not formally an acronym. A response may include the registrar, registration and expiration dates, nameservers, and contact details, although what is displayed depends on the TLD, registrar, privacy rules, and current policies. Public data is not always complete, and a WHOIS result alone does not constitute definitive legal proof of ownership or actual use.

How to Query

The traditional WHOIS protocol uses a text-based request and response model, often on TCP port 43, with web services offering more accessible interfaces. The person querying a server—managed by either a registry or registrar—receives information according to service rules. Historically, results had inconsistent formats and could be difficult to parse automatically. Frequency limits, CAPTCHAs, obfuscation, and variations between extensions affect availability. Rate limits, CAPTCHAs, redaction, and differences between extensions affect what a particular query can reveal.

The response may indicate the reference registrar, nameservers, and domain status, but not necessarily the DNS operator, website host, or content user. If registrant data is protected by a proxy service or redacted for privacy reasons, substitute contacts or unavailable fields may appear. A negative search does not prove a name is free: registries or registrars may maintain reserved statuses or withhold certain information publicly.

WHOIS and RDAP

RDAP, the Registration Data Access Protocol, is the modern standard developed to provide structured access to registration data. It offers uniform responses, international support, and differentiated access based on permissions. For gTLDs, RDAP has been the required authoritative source for registration data since January 28, 2025; WHOIS may remain available in some exceptions or as a fallback. The transition and service availability vary by TLD, so it is advisable to use official registry lookups or ICANN resources and verify which source generated the result.

RDAP does not make all personal data public. Display is limited by ICANN policies and applicable laws; some data may only be accessible to requesters with legitimate and proportionate purposes through specific procedures. Results can originate from either the registry or registrar, and it is not always clear which field was provided by each. For current data, an official source and query date are essential. This distinction ensures that users interpret results accurately and respect legal boundaries in data access.

Privacy and Responsible Use

Registration data may include personal information. Using it for spam, unwanted marketing, or harassment can violate terms and regulations. The mere visibility of a datum does not authorize its collection or redistribution. Users should review policies, limits, and permitted purposes. For non-public data disclosure requests, follow the registrar’s process or available programs without attempting to bypass controls.

In summary, WHOIS is a historical system for querying registration data, now supplemented and replaced in many contexts by RDAP. Coverage and privacy depend on the extension. A result should be interpreted as an indication of the queried service, not as absolute certification of ownership or usage freedom. Understanding these distinctions helps users navigate domain information responsibly and effectively.