- YUI Test
- JS Bin
- JSON Formatter
The JSON Formatter was created to help with debugging. As data expressed as JSON is often written without line breaks to save space, it became extremely difficult to actually read it. This tool hopes to solve the problem by formatting the JSON into data that is easily readable by human beings.
- Faux Console
Fiddler is a Web Debugging Proxy which logs all HTTP(S) traffic between your computer and the Internet. Fiddler allows you to inspect all HTTP(S) traffic, set breakpoints, and “fiddle” with incoming or outgoing data.
TamperData is a Firefox extension to track and modify http/https requests. You can use it for security testing of Web based applications and tracking request/responses.
- Live HTTP Headers
Allows you to view HTTP headers of a page while browsing. You can use Live HTTP Headers for debugging web application, find out which kind of web server the remote site is using, and see cookies sent by remote site.
- JSDoc Toolkit
- Dojo ShrinkSafe
- YUI Compressor
Editors & IDE
- Aptana Studio
- Komodo Edit
- Spket IDE
- Google’s AJAX APIs Playground
- QuirksMode – Compatibility Tables
Most popular source to check compatibility status of major web browsers for CSS2, CSS3, DOM Core, DOM HTML, DOM CSS, DOM Events and CSS Object Model View.
Glimmer is a desktop application that allows you to easily create interactive elements on your web pages by harnessing the power of the jQuery library. It allows you to easily create interactive experiences like rotating photo-galleries/mastheads,drop-down navigation, hover effects, or custom animations.
- jQuery Function Builder
You can use this tool to quickly build up a collection of functions that will be called when the page has loaded/is ready.
- Bookmarklet Maker
An online tools for creating regular expression
Other Browser Extensions
- Web Developer Extension For Firefox, Flock & Seamonkey
- Opera Dragonfly
- Developer Toolbar For IE6/7
The Microsoft Internet Explorer Developer Toolbar provides a variety of tools for quickly creating, understanding, and troubleshooting Web pages
- jQuery 1.3 Visual Cheat Sheet
This cheat sheet (6 pages) contains the full jQuery API reference with detailed descriptions and some sample code.
- jQuery 1.3 Cheat Sheet
This cheat sheet is a quick reference to functions and properties in the jQuery 1.3 library.
- jQuery Selectors Cheat Sheet
- MooTools 1.2 Cheat Sheet
It includes cheat sheet like documentation for Core, Native, Class, Element, Utilities and Request.
- Dojo 1.3 Base API Cheat Sheet
- Prototype 18.104.22.168 Cheat Sheet
Please feel free to suggest any addition to the list in your comments. You may also want to look at