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Security Headers vs HTTP Observatory: catalog facts
Security Headers	HTTP Observatory
Free Free to scan sites in the browser.	Free Free to use on the MDN website.
Web	Web
Simple A+ to F grade that is easy to share Option to hide results and follow redirects	Checks CSP, HSTS and other security headers Actionable recommendations tied to MDN documentation
Scans appear in a public recent list unless hidden Covers headers only, not TLS or application flaws	Focuses on headers and configuration, not full vulnerability scanning Only works for publicly reachable sites
Web application	Web application
Closed source	Closed source
License not stated	License not stated
Not stated if an account is needed	Not stated if an account is needed
Needs internet	Needs internet
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked September 23, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.