Improve the performance of your website with YSlow

Does your website have a habit of loading slowly? Sure you could blame it on your web server, but there is actually quite a lot you can do yourself to improve the loading time and performance of your website. YSlow is a Firefox add-on that integrates with Firebug to analyze a website and suggest ways of improving the performance of that site.

When you run YSlow on a web page it will analyze the page based on a set of rules (outlined below) then grade the web page based on these rules. Yslow also analyzes each component of the page and returns statistics as well as suggestions on how to improve each component of your site to achieve faster performance. As an example I ran YSlow on the Smashing Magazine website and discovered that they could improve their performance by simply combining background images into a CSS Sprite as well as combining their JavaScript files into one. This would reduce HTTP requests and hence improve website performance. You can see a screen shot from YSlow below.

Rules to speed up your website

  1. Minimize HTTP Requests
  2. Use a Content Delivery Network
  3. Add an Expires or a Cache-Control Header
  4. Gzip Components
  5. Put Stylesheets at the Top
  6. Put Scripts at the 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 the Buffer Early
  16. Use GET for AJAX Requests
  17. Post-load Components
  18. Preload Components
  19. Reduce the Number of DOM Elements
  20. Split Components Across Domains
  21. Minimize the Number of iframes
  22. No 404s
  23. Reduce Cookie Size
  24. Use Cookie-free Domains for Components
  25. Minimize DOM Access
  26. Develop Smart Event Handlers
  27. Choose
  28. over @import
  29. Avoid Filters
  30. Optimize Images
  31. Optimize CSS Sprites
  32. Don’t Scale Images in HTML
  33. Make favicon.ico Small and Cacheable
  34. Keep Components under 25K
  35. Pack Components into a Multipart Document
  36. Avoid Empty Image src

The above rules are based on these best practices for speeding up your website.

Download YSlow

YSlow is integrated into Firebug (a must have for all web designers) so you will need to download and install the Firebug add-on first. Once that is installed you can download the YSlow add-on.

Eventually I’ll get around to optimizing the performance of this site (hopefully).

Adham Dannaway

Web Designer and Front End Developer with a passion for web design, coding, blogging, WordPress and chewing gum. Check out my web design portfolio and follow me on Twitter and Facebook!

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