altdns vs SurfaceDiff: side-by-side comparison (2026)

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

SurfaceDiff: Continuous external attack surface monitoring that shows what changed between scans. Built by SurfaceDiff.

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

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

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