Web Performance Analysis & Optimization tools

 If you cannot measure it, you cannot improve it - Lord Kelvin

[Update:26-Dec-2016] - I got a chance to revisit the tools I listed below six years ago. I'll leave the original list as it is but below are what I would try in the future as they are extremely convenient to use -

1. Chrome Developer Tools, Audit tab (F12 keyboard shortcut)
2. Google Page Speed
3. WebPageTest
4. Web Page Analyzer
5. DOM Monster
6. YSlow

Following is the approach I would take to fix performance issues -
1. Run all the free perf tools to study the issues pointed out by them
2. Consolidate them based on which are serious & workable (not all suggestions may have easy fixes & there has to be a trade-off between usability, maintainability, security, SEO, cost & performance)
3. Make modifications & measure continuously

There are a bunch of free Web Performance Analysis & Optimization tools that web developers can take advantage of to build blazing fast web pages -

• Page Speed - open source Firebug plugin
• YSlow  - Firebug plugin from Yahoo
• AOL Pagetest - appears under the Tools menu in Internet Explorer after installation. Online version of Pagetest also provides Optimization Report.
• Zoompf -  this web-based service can detect over 300 possible issues & provide recommendations
• MSFast/MySpace’s Performance Tracker - IE browser plugin from MySpace
• VRTA  (Visual Round Trip Analyzer) - Microsoft tool that works along with Netmon
• neXpert - works with Fiddler. Especially useful for pages built with ASP.NET
• Web Page Analyzer - incorporates the latest best practices from the book Website Optimization
• Yottaa - measures performance, provides customized analytics & optimization tips 
• Torbit - provides realtime dashboard,  shows the loading times your visitors are experiencing right now and spot any performance issues that may be affecting a particular region. 
• Google's PageSpeed Insights analyzes the content of a web page, then generates suggestions to make that page faster.

These tools provide suggestions that not just cut page download time but also operational costs. I learnt about some of these tools from web performance guru Steve Souders' blog

Also see:
HOW TO improve the front-end performance of a website

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