HeaderCheck

Local security header audit. Runs offline. Made by YvonLabs.

HeaderCheck is a lightweight, privacy-respecting Chrome extension that analyzes HTTP response headers for the active tab and evaluates a site's security and privacy posture. It uses a deterministic weighted scoring model (SCM-2025.1) to calculate a 0–100 score based on the presence and validity of key security headers, including CSP, HSTS, COOP, COEP, CORP, Referrer-Policy, Permissions-Policy, X-Frame-Options, and X-Content-Type-Options. • Instant analysis • No remote calls or telemetry • Graded vs informational headers for clarity • Clean, minimal interface • Focused on modern browser security and privacy best practices • EU-aligned philosophy emphasizing transport integrity and referrer minimization HeaderCheck runs entirely on-device inside Chrome’s extension sandbox. No data leaves your browser, ever.