CORS Policy Builder & Analyzer
Build and statically analyze CORS response headers locally, with origin, credential and preflight guidance.
CORS controls which browser origins may read certain cross-origin responses. It is not authentication, authorization, CSRF protection, or a network firewall.
Policy controls
Response headers
Ready.
Presets are starting points. No server is contacted or tested. CORS primarily governs browser cross-origin reading, not same-origin access or direct server-to-server requests. Static headers cannot prove a deployed policy, authentication, application authorization or security.
Build response headers or inspect an existing policy.
The builder and analyzer share a normalized header model. Header names are case-insensitive. Unknown headers remain visible without semantic validation. Request Origin and Access-Control-Request-* fields are separated from response permissions. Errors withhold copy-ready output; warnings and recommendations require review. No server is contacted or tested.
Choose fixed or dynamic origin behavior.
A public, non-credentialed resource may intentionally use Access-Control-Allow-Origin: *. Credentialed responses require one explicit approved origin. ACAO cannot contain a comma-separated allowlist. A fixed origin independent of the request does not require Vary: Origin. For a dynamic allowlist, validate the request origin on the server, return only an approved origin, and merge Vary: Origin. The generated header illustrates one approved response; it does not implement server-side selection. Blind reflection and null origins require particular care.
Preflight is separate from authorization.
Allowed methods and headers describe preflight permissions; they do not eliminate preflight or authorize an application operation. With credentials included, wildcards in allowed methods, allowed headers and exposed headers are literal tokens. Authorization must be explicitly allowed even with a non-credentialed header wildcard. Browsers cap preflight caching independently of Max-Age. Exposing Set-Cookie does not make it readable by scripts.
Review static findings in context.
CORS controls which browser origins may read certain cross-origin responses. It is not authentication, authorization, CSRF protection, or a network firewall. It primarily governs browser cross-origin access, not same-origin or direct server-to-server requests. Presets are starting points. There are no numeric security scores or guarantees about deployment.
Input is limited to 8,192 ASCII characters, 64 header lines, 128-character names and 1,024-character values. Builder fields are bounded, with at most 16 dynamic origins. Origins must use serialized HTTP(S) form without paths, trailing slashes or default ports. Full Fetch simulation, network testing and framework configuration generation are outside scope.