Exceptional Performance

Yahoo!'s Exceptional Performance team promotes best practices for improving web page performance. They conduct research, build tools, write articles and blogs, and speak at conferences.

Best Practices

The Yahoo! Exceptional Performance team has identified a number of best practice rules for making web pages fast. They have identified 34 rules which are divided into seven categories.

Filter by category:

  • Content
  • Server
  • CSS
  • JavaScript
  • Images
  • Mobile
  • All
  1. Make Fewer HTTP Requests
  2. Use a Content Delivery Network (CDN)
  3. Add Expires or Cache-Control Header
  4. Gzip Components
  5. Put Stylesheets at Top
  6. Put Scripts at Bottom
  7. Avoid CSS Expressions
  8. Make JavaScript and CSS External
  9. Reduce DNS Lookups
  10. Minify JavaScript and CSS
  11. Avoid Redirects
  12. Remove Duplicate Scripts
  13. Configure ETags
  14. Make Ajax Cacheable
  15. Flush Buffer Early
  16. Use GET for Ajax Requests
  17. Postload Components
  18. Preload Components
  19. Reduce the Number of DOM Elements
  20. Split Components Across Domains
  21. Minimize Number of iframes
  22. Avoid 404s
  23. Reduce Cookie Size
  24. Use Cookie-Free Domains for Components
  25. Minimize DOM Access
  26. Develop Smart Event Handlers
  27. Choose <link> Over @import
  28. Avoid Filters
  29. Optimize Images
  30. Optimize CSS Sprites
  31. Do Not Scale Images in HTML
  32. Make favicon.ico Small and Cacheable
  33. Keep Components Under 25 KB
  34. Pack Components Into a Multipart Document
  35. Avoid Empty Image src

YSlow for Firebug YSlow icon

Use the YSlow tool to analyze a web pages and get a report on why the web page is slow based on the best practices for high performance web sites. YSlow is a Firefox add-on integrated with the Firebug web development tool. This tool has been used internally at Yahoo! by many properties (for example, Yahoo! Sports, Yahoo! Movies, Yahoo! News, and so on) to improve the performance of their web pages by anywhere from 25 to 50 percent. Yahoo! is happy to share this tool with the development community to help others accelerate their users' experiences on their web sites.


Research conducted by the Exceptional Performance team is documented in the following Yahoo! User Interface Blog articles.

Developer Support & Community

Web page performance and the YSlow tools are discussed in the Exceptional Performance Group. Contact this group if you have questions or need technical support.