A CORS preflight request is a CORS request that checks to see if the CORS protocol is understood and a server is aware using specific methods and headers.

It is an

[OPTIONS](https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/OPTIONS?ref=hackernoon.com)request, using three HTTP request headers:[Access-Control-Request-Method](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Request-Method?ref=hackernoon.com),[Access-Control-Request-Headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Request-Headers?ref=hackernoon.com), and the[Origin](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Origin?ref=hackernoon.com)header.

A preflight request is automatically issued by a browser and in normal cases, front-end developers don’t need to craft such requests themselves. It appears when request is qualified as “to be preflighted” and ommited for simple requests.

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