Using CORS Introduction APIs are the threads that let you stitch together a rich web experience. But this experience has a hard time translating to the browser, where the options for cross-domain requests are limited to techniques like JSON-P (which has limited use due to security concerns) or setting up a custom proxy (which can be a pain to set up and maintain). Cross-Origin Resource Sharing (CORS) is a W3C spec that allows cross-domain communication from the browser. By building on top of the XMLHttpRequest object, CORS allows developers to work with the same idioms as same-domain requests. The use-case for CORS is simple.