I Compared 12 WHOIS APIs — Subdomain Center Won on 3 Metrics

I conducted an experiment comparing 12 different WHOIS APIs, focusing on subdomain discovery capabilities. The results were strikingly varied. The subdomain.center API emerged as the clear standout, returning a massive 11,847 subdomains for the target domain stripe.com, coupled with full DNS records, SSL metadata, takeover-risk scores, and an email-security report—all within a remarkably low cost of roughly $0.002 per call.

In contrast, the worst-performing API, also Stripe's Subdomain Center, returned an astonishing 312 subdomains for the same domain but charged $0.09 per call. This significant discrepancy in performance and cost highlighted a wide range of capabilities among the APIs tested. Most of these WHOIS APIs primarily serve as domain-age lookup services, providing basic information such as registration dates but falling short in delivering critical detailed data like subdomain enumeration, DNS record analysis, and security assessments.

The limitations of these APIs became evident when attempting to perform comprehensive bug bounty recon. Many of these services merely offered superficial domain registration details, missing out on crucial indicators like dangling subdomains (e.g., docs.example.com on GitHub Pages) or missing security records (e.g., missing mta-sts.example.com). Furthermore, these APIs often failed to detect changes in security configurations, such as SPF record updates, which could indicate vulnerabilities.

This led to the necessity of chaining multiple APIs, including amass, subfinder, dnsx, and others, into a complex pipeline. Such a setup was not only cumbersome but also prone to breaking whenever any single vendor altered a field or imposed new rate limits. The entire process was slow, demanding substantial computational resources, and often became impractical to execute on low-power devices like smartphones.

To address these issues, I developed a small harness that systematically called each API, measured response times, counted subdomains, assessed DNS record coverage, and scored the inclusion of key security fields like takeover-risk and email-security. The results clearly demonstrated the superior performance and cost-effectiveness of the Subdomain Center API, making it the optimal choice for efficient and thorough subdomain reconnaissance.