The subject matter of this specification can be embodied in, among other things, a method that includes selecting a plurality of web pages including static web page elements, generating first configuration information that specifies at least one of the static web page elements, and generating second configuration information that specifies at least one asynchronous web page element. Each asynchronous web page element corresponds to a particular static web page element specified in the first configuration information. The method also includes modifying the selected plurality of web pages. The modification includes parsing the plurality of web pages, identifying the static web page elements within the plurality of web pages that are also specified in the first configuration information, and replacing the identified static web page elements with the corresponding asynchronous web page elements specified in the second configuration information.