Build Access-Control-Allow-* headers and Nginx CORS preflight blocks.
Execution runs 100% locally inside the browser sandbox using HTML5 Canvas, Web Cryptography Subtle API, and Web Workers. Zero egress.
Zero network latency. Operates completely offline with zero dependencies on third-party backend servers or cloud services.
Built according to official RFC specifications, cryptographic test vectors, and enterprise-grade data transformation standards.
Enter your client web origin (e.g. https://app.example.com).
Check allowed HTTP methods and custom header names.
Copy the response headers or Nginx server block.
It caches preflight OPTIONS responses in the browser, eliminating unnecessary preflight roundtrips.
No, browsers reject Access-Control-Allow-Credentials: true if Origin is set to *.
Zero-egress companion tools in the Security & Network suite
Audit CSP, HSTS, X-Frame-Options, and security headers with OWASP grading (A+ to F).
Measure cryptographic randomness, Shannon entropy (0-8 bits/byte), Chi-square test, and byte distributions.
Generate secure RFC 6238 Base32 TOTP secret keys and standard otpauth:// URIs for Google Authenticator.
Construct and validate HTTP CSP headers and meta tags.
