What is a Domain Availability API?
A domain availability API lets you programmatically check if domain names are available for registration. These APIs query RDAP/WHOIS databases in real-time and return availability status, making them essential for domain registrars, marketplaces, and brand protection tools.
Why DomScan is #1
- Generous free tier: 10,000 credits/month with no credit card
- Widest TLD coverage: 1,500+ extensions supported
- Modern REST API with JSON responses and excellent docs
- Unique MCP integration for AI assistants like Claude
- All-in-one: availability, valuation, DNS, brand monitoring
Best Domain Availability APIs - Top 10
DomScan
Our Pick Free Tier- Generous free tier: 10,000 credits/month with no credit card
- Widest TLD coverage: 1,500+ extensions supported
- Modern REST API with JSON responses and excellent docs
WhoAPI
Runner Up Free Tier- Established since 2011
- Comprehensive WHOIS parsing
- Good for bulk availability checks
Domainr (Fastly)
Free Tier- Backed by Fastly infrastructure
- Creative domain suggestions
- Lower-volume option via RapidAPI
Whoxy
- Strong historical WHOIS and reverse WHOIS coverage
- Pay-as-you-go entry point for batch research
- Good fit for WHOIS-heavy investigations and reseller tools
WhoisXML API
Free Tier- Very broad domain and infrastructure coverage
- Historical WHOIS, DNS, and threat data
- Enterprise packages for security workflows
WHOISJSON
Free Tier- Covers WHOIS, DNS, SSL, and availability in one API
- Simple entry pricing and low-friction onboarding
- Useful free tier for early testing and prototypes
DNSimple
- Full registrar with API
- Excellent documentation
- SSL certificate automation
RDAP API
Free Tier- Focused RDAP experience for domains, IPs, and ASNs
- Cleaner fit for modern registration-data workflows
- Good option for teams that do not need a huge platform
DomainTools
- Decades of historical WHOIS data
- Advanced threat intelligence
- Iris, DNSDB, and monitoring products
IP2WHOIS
Free Tier- Straightforward WHOIS lookup coverage
- Part of IP2Location ecosystem
- Useful alongside IP2Location data
Detailed Reviews
DomScan Review
DomScan is the most developer-friendly domain intelligence API available today. Built on modern standards with a focus on real-time RDAP data, it offers unmatched TLD coverage and innovative AI integration.
Pros
- Industry-leading 1,500+ TLD support
- Generous free tier (10K credits/month)
- Clean REST API with JSON responses
- Unique MCP server for AI assistants
Cons
- Newer service (less track record than older providers)
- No historical WHOIS data yet
Our Verdict
DomScan is our top pick for developers building domain-related applications in 2026. The combination of wide TLD coverage, generous free tier, and modern API design makes it the clear choice for most use cases.
WhoAPI Review
WhoAPI has been a reliable domain data provider since 2011, offering solid availability checking and WHOIS lookups. While it lacks some modern features, its proven reliability makes it a safe enterprise choice.
Pros
- 13+ years of operational history
- Reliable uptime and performance
- Good bulk checking capabilities
- Established enterprise reputation
Cons
- Higher pricing than alternatives
- Free trial limited to 30 days
- No AI/MCP integration
Our Verdict
WhoAPI is a solid choice for enterprises that prioritize proven reliability over cutting-edge features. The higher price point is justified for mission-critical applications where uptime is paramount.
Domainr (Fastly) Review
Domainr, now part of Fastly, pioneered creative domain suggestions and instant availability checking. While the original API is deprecated, the Fastly-powered service remains useful for domain discovery applications.
Pros
- Excellent domain suggestions
- Fastly infrastructure (fast and reliable)
- Good free tier for basic use
- Clean, simple API for basic use cases
Cons
- Original API deprecated
- Enterprise pricing not transparent
- Limited to availability (no valuation, DNS)
Our Verdict
Domainr is best suited for applications focused on domain discovery and creative suggestions. The Fastly backing ensures reliability, but the feature set is narrower than comprehensive alternatives.
Whoxy Review
Whoxy focuses on live WHOIS, historical WHOIS, reverse WHOIS, and batch lookup workflows for researchers, resellers, and brand-protection teams.
Pros
- Strong historical WHOIS and reverse WHOIS coverage
- Pay-as-you-go entry point for batch research
- Good fit for WHOIS-heavy investigations and reseller tools
Cons
- No domain valuation workflow
- Limited AI or modern workflow integrations
- Narrower feature set outside WHOIS and DNS research
Our Verdict
Whoxy focuses on live WHOIS, historical WHOIS, reverse WHOIS, and batch lookup workflows for researchers, resellers, and brand-protection teams.
WhoisXML API Review
WhoisXML API is the go-to solution for enterprise security teams and researchers needing comprehensive threat intelligence and historical domain data. It is powerful but complex.
Pros
- Comprehensive threat intelligence
- Historical WHOIS data access
- Strong security research focus
- Extensive API coverage for security use cases
Cons
- Complex pricing structure
- Overkill for simple availability checks
- Steeper learning curve
Our Verdict
WhoisXML API excels at enterprise security use cases. If you need historical WHOIS data or threat intelligence, it is excellent. For simpler availability checking, it is unnecessarily complex and expensive.
WHOISJSON Review
WHOISJSON packages WHOIS, DNS, SSL certificate, and availability lookups into a lightweight API for teams that need practical lookup coverage without enterprise overhead.
Pros
- Covers WHOIS, DNS, SSL, and availability in one API
- Simple entry pricing and low-friction onboarding
- Useful free tier for early testing and prototypes
Cons
- Less historical depth than larger intelligence platforms
- Smaller ecosystem and fewer enterprise references
- Limited threat-intel and monitoring depth
Our Verdict
WHOISJSON packages WHOIS, DNS, SSL certificate, and availability lookups into a lightweight API for teams that need practical lookup coverage without enterprise overhead.
DNSimple Review
DNSimple is a premium domain registrar with a beautifully designed API. If you need domain management alongside availability checking, it is an excellent choice - but it is pricier than API-only alternatives.
Pros
- Excellent API design and documentation
- Full registrar capabilities
- SSL certificate automation
- Great developer experience and support
Cons
- Requires subscription ($29+/mo)
- Fewer TLDs than dedicated APIs
- No free tier for API access
Our Verdict
DNSimple is ideal if you need both domain registration and API access in one package. The excellent documentation and API design justify the premium, but it is overkill for availability-only needs.
RDAP API Review
RDAP API centers on RDAP lookups for domains, IP ranges, and ASNs for teams that want structured registration data without buying a larger intelligence platform.
Pros
- Focused RDAP experience for domains, IPs, and ASNs
- Cleaner fit for modern registration-data workflows
- Good option for teams that do not need a huge platform
Cons
- No valuation, threat monitoring, or naming workflow
- Limited DNS and enrichment depth compared with broader platforms
- Smaller market footprint than established incumbents
Our Verdict
RDAP API centers on RDAP lookups for domains, IP ranges, and ASNs for teams that want structured registration data without buying a larger intelligence platform.
DomainTools Review
Enterprise-grade domain intelligence and threat detection platform
Pros
- Decades of historical WHOIS data
- Advanced threat intelligence
- Iris, DNSDB, and monitoring products
- Enterprise security teams, SOC analysts, threat hunters, forensic investigators, brand protection at scale
Cons
- Enterprise-only pricing
- Overkill for simple availability checks
- Limited fit for developer-first or low-volume projects
Our Verdict
DomainTools is the undisputed leader in enterprise threat intelligence and historical domain data. If you need decades of WHOIS history or advanced threat analysis for a security operations center, it is unmatched. However, for developers building domain tools or startups, the pricing is prohibitive and the feature set is excessive.
IP2WHOIS Review
WHOIS lookup API integrated with IP2Location ecosystem
Pros
- Straightforward WHOIS lookup coverage
- Part of IP2Location ecosystem
- Useful alongside IP2Location data
- Developers needing simple WHOIS lookups, IP2Location ecosystem users, fraud prevention teams
Cons
- No DNS lookup features
- Limited bulk and historical workflows
- Limited to WHOIS data
Our Verdict
IP2WHOIS offers a solid WHOIS lookup API with excellent TLD coverage and a reasonable free tier. The integration with IP2Location products is valuable for teams already in that ecosystem. For simple WHOIS lookups, it delivers, but the lack of historical data and bulk operations limits its appeal for advanced use cases.
How We Rank
Our rankings combine hands-on product testing with public pricing pages, official API documentation, TLD or dataset coverage, documentation quality, and overall developer experience.
Last updated: July 2026