When a web server responds to an HTTP request, typically the response contains a "Content-Type" field in the HTTP header. A ThousandEyes page load test requires the target of the test (the URL field of the configuration page) to have a content-type of either "text/html" or "application/xhtml". When saving a page load test's configuration, the ThousandEyes platform requests the URL and checks the response's content-type to ensure that the content-type is one of these values. If the target of the page load test does not have either of these values, the test configuration page displays an error upon attempting to save the configuration. For example, if the target is a JPEG image, the test configuration page displays the following error: