HTTP
CORS Analyzer
Check origin matching, credential rules, preflight methods and headers, exposed fields, and max-age without sending a request.
How this tool works
CORS is enforced by browsers around cross-origin script access. A server can receive and process a request even when the browser later prevents JavaScript from reading the response.
A credentialed request cannot pair with a wildcard allowed origin. A preflight must authorize the proposed method and non-safelisted request headers. Safelisted response headers are readable by default; other frontend-required headers need explicit exposure, and credentialed mode does not give * wildcard semantics. Max-age describes preflight caching and browser caps can shorten it.
Examples
- Allow one exact origin.
- Flag wildcard origin with credentials.
- Find a requested header missing from the preflight response.
Common use cases
Diagnostic sequence
- Record the browser page origin exactly.
- Separate the preflight response from the actual response.
- Check allowed origin and credential mode.
- For preflight, compare method and requested header names case-insensitively.
- Use browser console and network evidence to confirm the modeled result.
Security boundary
Allowing a browser origin does not grant user permission, validate a bearer token, prevent CSRF in every design, or protect a server endpoint from non-browser clients.
Failure case: CORS
Invalid/failure example
Find a requested header missing from the preflight response.
Expected: A credentialed request cannot pair with a wildcard allowed origin. A preflight must authorize the proposed method and non-safelisted request headers. Safelisted response headers are readable by default; other frontend-required headers need explicit exposure, and credentialed mode does not give * wildcard semantics. Max-age describes preflight caching and browser caps can shorten it.
Related guides
Official references
FAQ
Does this tool send the pasted data or execute an API request?
No. Analysis runs in this browser tab. The tool does not call pasted URLs, resolve remote references, or submit the input to a DevPouch processing endpoint.
Is CORS an authentication system?
No. CORS controls whether browser script can access a cross-origin response. Servers must still authenticate and authorize requests.
Can this reproduce every browser decision?
It models exact origin, credentials, preflight method and headers, exposed response headers, and max-age from supplied data. Redirects, private network access, service workers, cookies, request mode, and browser version can add context.