This document describes, among other things, a computer-implemented method that can include receiving, from a web server system, web page code to be provided over the internet to a computing device. The web page code can correspond to a particular web page served by the web server system. The method may include generating an intermediate representation of at least a portion of the web page code, and comparing the intermediate representation to a prior intermediate representation of the particular web page. Based on a result of the comparison, the method can include determining what portion of the web page code to analyze for re-coding of the web page code before serving the web page code to the computing device.