Structured WHOIS & RDAP Data for Developers
Look up domain data, explore modern RDAP, and integrate clean JSON with our free developer API.
Domain Data for Building and Research
Start with a clean API or use focused tools for RDAP, WHOIS history, related domains, and domain research.
Developer API
Get structured domain data in clean JSON and integrate WHOIS, RDAP, DNS, and analysis into your application.
RDAP Lookup
Query the modern RDAP protocol for structured domain registration data with richer fields than WHOIS — conformant with RFC 7482.
WHOIS History
Track ownership changes, registrar transfers, and nameserver updates with historical WHOIS snapshots and diff comparison.
Related Domains
Discover domains sharing the same registrant, nameservers, or IP for brand protection and domain research.
WHOIS Lookup
Check registration details, nameservers, and expiration dates for any domain.
Domain Health Score
Get a comprehensive A+ to F grade covering SSL, DNS, email security, security headers, and domain age.
Expiring Domains
Browse domains expiring soon. Valuable for domain investors to discover premium domains becoming available.
Reverse IP Lookup
Find all domains hosted on the same IP address. Useful for security research and hosting analysis.
WHOIS Compare
Compare two domains side by side — registration data, DNS, and ownership with a similarity score.
Frequently Asked Questions
Quick answers about domain lookup tools and services
What is WHOIS lookup?
WHOIS lookup is a query protocol that retrieves registration information about a domain name, including the registrar, registrant, creation date, expiration date, nameservers, and contact details. Whose.Domains provides free, instant WHOIS lookups for any domain.
What is RDAP?
RDAP (Registration Data Access Protocol) is the modern replacement for WHOIS. It provides structured, machine-readable domain registration data via RESTful HTTP APIs, with better internationalization and access control support.
How do I check if a domain is available?
Use the Domain Availability Checker. Enter your desired domain name and we'll instantly check its registration status across multiple TLD extensions like .com, .net, .org, .io, and more.
What is a Domain Health Score?
Domain Health Score is a comprehensive grading system (A+ to F) that evaluates a domain's SSL configuration, DNS setup, email authentication (SPF/DKIM/DMARC), security headers, and domain age to assess overall domain quality.
Is the Whose.Domains API free?
Yes, Whose.Domains offers a free RESTful API for developers to access WHOIS data, DNS records, domain history, SSL certificate info, and domain scoring programmatically. Visit our API Documentation page for details.