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 Smush.it™ and JSLint.
How Do I Get Started?
- Install Firebug
- Download YSlow
- Review the YSlow User Guide
Learn More
Best Practices
Click here to learn more about the best practices for making high performance web sites.
Smush.It™
Read more about how the Smush.it™ 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 Smush.it service, which is subject to the Smush.it Terms of Use.
Recent Blog Articles 
Wed, 29 Apr 2009
YSlow 2.0 early preview in China
Sun, 28 Dec 2008
YUI Theater — Douglas Crockford: "Ajax Performance"
Tue, 23 Dec 2008
YUI Theater — Nicole Sullivan: "Design Fast Websites (Don’t Blame the Rounded Corners)"
Tue, 23 Dec 2008
Image Optimization, Part 5: AlphaImageLoader
Mon, 08 Dec 2008
Yahoo! Groups Discussions
view all
Fri, 03 Jul 2009
Re: flushing as mentioned in the "Best Practices"
Fri, 03 Jul 2009
flushing as mentioned in the "Best Practices"
Fri, 03 Jul 2009
Re: open-source PHP CSS sprite generator?
Fri, 03 Jul 2009