CORS preflight explainer 🌐
Choose a method and request headers to see if a cross-origin browser request would likely send an OPTIONS preflight.
Debounced. Educational only — real browsers also consider mode, redirects, and service workers.
May be a simple request
- Method
GETis CORS-safelisted. - Headers: look safelisted for this check.
Notes
- This combination can be a “simple” cross-origin request: no preflight, but the response must still include a valid Access-Control-Allow-Origin (and credentials rules apply if cookies are sent).
How to use this
CORS-safelisted methods are GET, HEAD, and POST. Other methods require preflight. Safelisted request headers are limited (for example Accept, Accept-Language, Content-Language, and Content-Type with specific values). Authorization and JSON Content-Types typically trigger preflight.
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