Common symptoms
- Browser says blocked by CORS policy
- Preflight OPTIONS request fails
- API works server-side but not in browser
- Credentialed request is rejected
CORS Error Blocking an API? Diagnose the Cross-Origin Request
CORS is enforced by the browser based on the server's response policy. A failed request may need a narrow origin, credential, method, or header correction; using a wildcard everywhere can create security problems without fixing authenticated requests.
Possible causes
- Origin not allowed
- Preflight response incomplete
- Credentials used with wildcard origin
- Required header not allowed
- Request sent to the wrong API host
Diagnose the exact failure before choosing a repair.
Genesis separates the visible symptom from the underlying technical cause. Run the supported diagnostic first, review the evidence, and then use a matching repair only when the failure is actually verified.
- Platform scope
- Web applications and APIs
- Category
- Applications & APIs
- Last updated
- 2026-09-13
Next step
Start with a free diagnostic. If Genesis verifies a problem and a compatible treatment exists, it will route you to the relevant Code Store product or repair path.
Run a Website Diagnostic