Steve Souders' book, High Performance Web Sites, describes the 14 best practices he developed while working as the Chief Performance Yahoo! YSlow, the Firebug extension he created, codified those best practices. Now working at Google, Steve discusses the next set of best practices he's discovered, including how to load scripts without blocking and where to place (and where not to place) inline scripts. These guidelines focus on the front-end, where 80-90% of the end-user response time is spent, and have proven to reduce response times of major Web sites by 25-50%. This phenomenon, where a majority of the user response time is spent in the front-end, holds true for most Web sites, including the ten most-visited U.S. Web sites. In any optimization effort it's critical to profile current performance to identify where the greatest improvement can be made. It's clear that the place to focus is front-end performance.
- There is more potential for improvement by focusing on the front-end. Making the back-end twice as fast reduces response times by 5-10%, whereas making the front-end twice as fast saves 40-45%.
- Front-end improvements typically require less time and resources than back-end performance projects.
- Focusing on front-end improvements has been proven to work. Development teams working on the world's largest Web sites have reduced their end-user response times by following the best practices described here.