Reining in MobileWeb Performance with Document and Permission Policies

The quality of mobile web experience remains poor, partially as a result of complex websites and design choices that worsen performance, particularly for users on suboptimal networks or with low-end devices. Prior proposed solutions have seen limited adoption due to the demand they place on developers and content providers, and the performing infrastructure needed to support them. We argue that Document and Permissions Policies - ongoing efforts to enforce good practices on web design - may offer the basis for a readily-available and easily-adoptable solution, as they encode key best practices for web development. In this paper, as a first step, we evaluate the potential performance cost of violating these well understood best practices and how common such violations are in today's web. Our analysis shows, for example, that controlling for unsized-media policy, something applicable to 70% of the top Alexa websites, can indeed significantly reduce Cumulative Layout Shift, a core metric for evaluating the performance of the web.