XMLHttpRequest (XHR) is an API available in web browser scripting languages such as JavaScript. It is used to send HTTP or HTTPS requests directly to a web server and load the server response data directly back into the script.^[1] Development versions of all major browsers support URI schemes beyond http: and https:, in particular, blob: URLs are supported. The data might be received from the server as JSON^[2], XML^[3], HTML, or as plain text.^[4] Data from the response can be used directly to alter the DOM of the currently active document in the browser window without loading a new web page document. The response data can also be evaluated by client-side scripting. For example, if it was formatted as JSON by the web server, it can easily be converted into a client-side data object for further use.

XMLHttpRequest has an important role in the Ajax web development technique. It is currently used by many websites to implement responsive and dynamic web applications. Examples of these web applications include Gmail, Google Maps, Facebook and many others.^{[citation needed]}

XMLHttpRequest is subject to the browser's same origin policy in that, for security reasons, requests will only succeed if they are made to the same server that served the original web page. There are alternative ways to circumvent this policy if required.