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Exceptional Performance
Yahoo!'s Exceptional Performance team evangelizes best practices for improving web performance. They conduct research, build tools, write articles and blogs, and speak at conferences. Their best practices center around the rules for high performance web sites.
Best Practices
The Exceptional Performance team has identified a number of best practices for making web pages fast. The list includes 34 best practices divided into 7 categories.
Filter by category:
- Content
- Server
- Cookie
- CSS
- Javascript
- Images
- Mobile
- All
- Make Fewer HTTP Requests
- Use a Content Delivery Network
- Add an Expires or a Cache-Control Header
- Gzip Components
- Put Stylesheets at the Top
- Put Scripts at the Bottom
- Avoid CSS Expressions
- Make JavaScript and CSS External
- Reduce DNS Lookups
- Minify JavaScript and CSS
- Avoid Redirects
- Remove Duplicate Scripts
- Configure ETags
- Make Ajax Cacheable
- Flush the Buffer Early
- Use GET for AJAX Requests
- Post-load Components
- Preload Components
- Reduce the Number of DOM Elements
- Split Components Across Domains
- Minimize the Number of iframes
- No 404s
- Reduce Cookie Size
- Use Cookie-free Domains for Components
- Minimize DOM Access
- Develop Smart Event Handlers
- Choose <link> over @import
- Avoid Filters
- Optimize Images
- Optimize CSS Sprites
- Don't Scale Images in HTML
- Make favicon.ico Small and Cacheable
- Keep Components under 25K
- Pack Components into a Multipart Document
YSlow for Firebug 
YSlow analyzes web pages and tells you why they're slow based on the best practices for high performance web sites. YSlow is a Firefox add-on integrated with the popular Firebug web development tool. This tool has helped improve the performance on over 50 Yahoo! properties by 25-50%. We're pleased to be able to share this with the development community so that others can join us in accelerating the user experience on the web!
Research
Research conducted by the Exceptional Performance team is documented in the following Yahoo! User Interface Blog articles.
- Performance Research, Part 1: What the 80/20 Rule Tells Us about Reducing HTTP Requests
- Performance Research, Part 2: Browser Cache Usage - Exposed!
- Performance Research, Part 3: When the Cookie Crumbles
- Performance Research, Part 4: Maximizing Parallel Downloads in the Carpool Lane
- Performance Research, Part 5: iPhone Cacheability - Making it Stick
Developer Support & Community
YSlow and performance topcis are discussed on the Exceptional Performance Group. Use this group if you have questions, issues, or need technical support.
You can also send feedback and report YSlow bugs and feature requests using the feedback form.
High Performance Videos
Along with the general web developments videos, you can also enjoy several performance-related videos now available on YUI Theater.
High-Performance Books by Yahoo!s
Recent Blog Articles 
view all
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
Tue, 30 Jun 2009
Tue, 30 Jun 2009
Tue, 30 Jun 2009
RFC: add checks for onresize event handler.
Sun, 28 Jun 2009
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