Yahoo! YSlow

YSlow analyzes web pages and suggests ways to improve their performance based on a set of rules for high performance web pages. YSlow is a Firefox add-on integrated with the Firebug web development tool. YSlow grades web page based on one of three predefined ruleset or a user-defined ruleset. It offers suggestions for improving the page's performance, summarizes the page's components, displays statistics about the page, and provides tools for performance analysis, including™ and JSLint.

How Do I Get Started?

  1. Install Firebug
  2. Download YSlow
  3. Review the YSlow User Guide

Learn More

Best Practices

Read more about the best practices for making high performance web sites.


Read more about how the™ tool can help optimize web page image files.

Frequently Asked Questions

If you have questions about YSlow, check the frequently asked questions for the product.

Developer Community and Support

YSlow development is discussed in the Exceptional Performance group; this group was formed by Yahoo!'s Exceptional Performance team as a forum for communicating about web performance. Contact this group for assistance with YSlow questions, issues, or technical support.

License Agreement

YSlow's source files are available through Open Source. For more information, refer to YSlow License Agreement.

Ready to get started?

YSlow uses Yahoo!'s service, which is subject to the Terms of Use.