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If you want to improve the performance of your website, it's best to start with a thorough analysis to understand which changes would yield the most dramatic improvements. Several free tools are available that can help you to understand the structure and resulting limitations of your website:

  • YSlow generates a nice performance summary. Because it's tailored to Yahoo!'s internal needs, it's best suited for large websites (or you could ignore rules that don't apply to your network).
  • Pingdom tools measure the performance of your website from the perspective of a distant visitor (Pingdom's server), but its behavior differs significantly from the behavior of a typical web browser. (It uses too many parallel HTTP sessions and it doesn't block further HTTP downloads when downloading JavaScript libraries.)
  • IBM Page Detailer gives you a nice graphic representation of the requests made by your browser, but it cannot emulate the long response time experienced by international visitors.
  • Fiddler, one of the best HTTP debugging tools, can generate performance summaries or request timelines, but it suffers from the same limitations as Page Detailer—you'll see local response times if the server is close to your browser.

After identifying the typical web page structure in your website, you almost always can gain performance by making these changes:

  • Set the HTTP caching headers (Expires and Max-age) on static files (images, JavaScript libraries, and CSS stylesheets).
  • Enable HTTP compression (assuming that your server has sufficient CPU capacity).
  • Move CSS stylesheets (LINK elements) to the top of the page and JavaScript libraries (SCRIPT elements) to the bottom of the page.
  • Optimize your HTML code. Use CSS for page formatting and don't use HTML tables for page layout.
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