YSlow’s Performance Analysis

YSlow, is an extension to Firebug, is available within Firefox. It generates a score for each rule and an overall score based on a weighted average of the individual rule scores. It also displays a list of all the resources used in the page as well as overall statistics (number of requests, total page weight, etc.).

The basic rules of YSlow’s Performance Analysis

  1. Minimize HTTP Requests
  2. Use a Content Delivery Network
  3. Avoid empty src or href
  4. Add an Expires or a Cache-Control Header
  5. Gzip Components
  6. Put StyleSheets at the Top
  7. Put Scripts at the Bottom
  8. Avoid CSS Expressions
  9. Make JavaScript and CSS External
  10. Reduce DNS Lookups
  11. Minify JavaScript and CSS
  12. Avoid Redirects
  13. Remove Duplicate Scripts
  14. Configure ETags
  15. Make AJAX Cacheable
  16. Use GET for AJAX Requests
  17. Reduce the Number of DOM Elements
  18. No 404s
  19. Reduce Cookie Size
  20. Use Cookie-Free Domains for Components
  21. Avoid Filters
  22. Do Not Scale Images in HTML
  23. Make favicon.ico Small and Cacheable
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