crt.sh vs Knock: Side-by-Side Comparison (2026)
Features, pricing, ratings, and pros and cons, compared head to head.
crt.sh is a free external attack surface management tool. Knock is a free external attack surface management tool. Compare features, ratings, integrations, and community reviews side by side to find the best external attack surface management fit for your security stack. Independent and vendor-neutral: our scores and rankings are earned, never bought — sponsored placement is always labeled.
CST VerdictShort answer
Security teams doing threat intelligence or domain monitoring should use crt.sh as a free, fast way to spot certificate issuance anomalies that signal domain takeover or phishing campaigns before they scale. Certificate Transparency logs index roughly 15 billion certificates, giving you real-time visibility into what's been legitimately issued against your domains and competitors' infrastructure. Skip this if you need automated alerting or integration into your SIEM; crt.sh is a lookup tool, not a monitoring platform, and catching malicious certificates requires manual checks or custom scripting. Security teams doing external attack surface reconnaissance on a budget should start with Knock; it's free, it works, and the 4,054 GitHub stars reflect actual adoption rather than marketing hype. The tool excels at the narrow job of subdomain enumeration, which maps NIST Govern and Identify functions by forcing you to know what's actually exposed before you can defend it. Skip Knock if you need continuous monitoring or API integration into your existing ASM stack; this is a point-in-time scanner you run manually, not a platform that feeds ongoing discovery into your risk register.
Based on our analysis of core features, integrations, company size fit, deployment model, here is our conclusion:
