altdns vs crt.guru: side-by-side comparison (2026)

altdns: A tool for generating permutations, alterations and mutations of subdomains and resolving them.

crt.guru: External TLS cert monitoring with expiry alerts, vuln scanning & compliance reports. Built by Crt.guru.

The table above shows where their features, integrations, deployment and company size fit differ.

altdns is open-source with 2,439 GitHub stars. crt.guru is made by Crt.guru. The vendor behind a product decides its roadmap, support, and longevity, so check each company's profile before you commit.

Often, yes. altdns and crt.guru are both External Attack Surface Management products. Key differences: altdns is Free while crt.guru is Commercial, altdns is open-source. Use the table above to see where features, deployment and company size fit differ.