What Does It Test
Page Speed analyzes the performance of a page based on a set of 26 rules (as of version 1.7) that Google has documented. Each rule is given a priority code based on how great the potential impact would be on the page load time. Once Page Speed has determined which rules are broken, it gives the page a score between 0 and 100, which can be exported in JSON format, or sent straight to ShowSlow.com - a tool for recording YSlow and Page Speed scores over time.