From Google
Web page analysis
Page Speed -
Open source Firefox/Firebug Add-on that evaluates the performance of web pages and gives suggestions for improvement.
Chrome Developer Tools -
Tools included in Google Chrome that let you edit, debug, and monitor CSS, HTML, and JavaScript live in any web page. You can also use them to optimize web page performance by profiling CPU and memory usage.
Speed Tracer -
Google Chrome extension that helps you debug performance problems with AJAX applications.
Resource Optimization
Closure Compiler -
Optimize the speed and size of your JavaScript.
WebP -
Reduce image file sizes and download times.
Development tools
Closure Tools -
Use the Closure Compiler, Closure Library, and Closure Templates to build rich web applications with JavaScript that is faster, more powerful, and more optimized.
Google Web Toolkit -
Toolkit that allows you to build rich web applications in Java, and then compile into highly optimized JavaScript.
From other developers
Development
Cuzillion -
Tool for quickly constructing web pages to see how components interact and how behavior differs across browsers, sometimes in unexpected ways. Also lets you share sample pages with others.
Hammerhead -
Firebug Add-on for measuring the load time of web pages.
OOCSS -
Development environment and framework for creating fast, reusable CSS objects and modules.
Performance benchmarking
httperf -
Tool for generating HTTP workloads and measuring web server performance, and constructing micro- and macro-level benchmarks.
mon.itor.us -
Provides a personalized Ajax dashboard interface, checks server performance and availability, generates uptime reports, tracks visitors, checks CPU, memory and other systems resources, and alerts when it detects abnormalities.
Pylot -
Open source tool for testing the performance and scalability of web services. It runs HTTP load tests, verifies server responses, and produces reports with metrics.
Wbox -
Performs various tests, including page load benchmarking, web server and web application stress testing, and verifies correct configuration of virtual domains configuration, redirects, and HTTP compression.
JavaScript profiling
dynaTrace AJAX -
Full tracing analysis of Internet Explorer 6-8 (including JavaScript, rendering, and network traffic). (Related blogpost)
PHP profiling
Xdebug -
Extension for PHP that provides profiling and code coverage analysis, as well as debugging information including stack and function traces, and memory allocation.
XHProf by Facebook -
Instrumentation-based hierarchical profiler for PHP.
Resource optimization
CSS Sprite Generator -
Generates a CSS sprite out of a number of images.
JSLint -
Tool that looks for code quality problems in JavaScript programs.
JSMin -
Filter which removes comments and unnecessary whitespace from JavaScript files.
Smush It -
Online tool that allows you to upload images for lossless compression and optimization. Provides a report of bytes saved and downloads a zip file containing the optimized versions of the files.
SpriteMe! -
Tool that determines background images to sprite, groups and sprites them, and generates resultant modified CSS.
YUI Compressor -
JavaScript minifier designed to yield a higher compression ratio than other tools.
Web debugging
Fiddler 2 -
Web debugging proxy which logs all HTTP/S traffic between your computer and the Internet. Inspect HTTP/S traffic, set breakpoints, and "fiddle" with incoming or outgoing data.
Firebug -
Firefox Add-on that lets you edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.
HttpWatch -
HTTP viewer and debugger integrated with IE and Firefox to provide HTTP/S monitoring without leaving the browser window.
Web page analysis
AOL Page Test -
Open source tool for measuring and analyzing web page performance using Internet Explorer.
BrowserMob -
Tool for website performance monitoring and alerting.
IBM Page Detailer -
Graphical tool that assesses web page performance and provides details include the timing, size, and identity of each item in a page.
IntroSpectrum -
Web-based performance monitor which simulates users using actual web browsers.
Microsoft VRTA -
Tool that visualizes web page download, identifies areas for performance improvements, and recommends solutions.
MySpace Performance Tracker -
Internet Explorer browser plugin that helps improve web page performance by capturing and measuring possible bottlenecks.
WebPagetest -
Tool that provides a waterfall of your page load performance as well as a comparison against an optimization checklist.
Yahoo! YSlow -
Firefox/Firebug Add-on that analyzes web pages and suggests ways to improve their performance, based on a set of rules for high performance web pages.
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