Application responsiveness over a network, such as for a web site or web-based application, is monitored and optionally recorded by tracking actual end users interacting with the application and the time it takes for their requested web pages to load. The process involves a web server that sends instrumented web pages or pointers to such instrumentation code in response to browser requests. This instrumentation causes scripting code on the client browser to gather data sufficient to enable determination of how long the page took to load, with separate measurements for latency time and/or intra-page load time, and to classify the type of request for which the measurements correspond. The scripting code can report the values to a record keeper or an external process. In one embodiment, Page Lifecycle Events are used to track and update a Marker and Timestamp from which the page load times and classifications are derived.