15 Helpful In-Browser Web Development Tools


There are many useful Web development tools that integrate in your browser. These in-browser tools are commonly known as add-ons or extensions. Though add-ons and extensions aren’t just for Web development, many of them out there are designed specifically for Web developers. In-browser tools vary greatly in the jobs they perform; for example, some of them help you diagnose issues with CSS, HTML and JavaScript, while others evaluate the accessibility of your website.

In this article, we explore some of the most popular and useful in-browser Web development tools. You’ll find tools for popular Web browsers like Firefox and Internet Explorer. Whether you need to debug and inspect your HTML, inspect HTTP headers, access FTP source files, evaluate accessibility or just figure out what color a Web page element is, you may find a variety of tools discussed here useful.


Firebug - screen shot.1

Firebug2 is an extension for the Mozilla Firefox browser that allows you to debug and inspect HTML, CSS, the Document Object Model (DOM) and JavaScript. Though it has many strong features, it’s most known for revolutionizing the way developers debug and profile JavaScript code.

For example, before Firebug, many developers would use the alert() function to see what a variable contains or to find what line the code breaks. With Firebug enabled, you’re told specifically what the error is and which line it comes from. Firebug is an excellent tool for AJAX application developers because it lets you explore and perform on-the-fly edits on the DOM to see what happens when you manipulate Web page elements after a user action.

Aside from its popular JavaScript and DOM functionalities, Firebug can also log network activity to allow you to see detailed results of HTTP connections, inspect and edit HTML on the fly and debug and visualize your CSS.

Further Reading

Web Developer

Web Developer - screen shot.6

The Web Developer7 extension (for the Firefox, Flock and SeaMonkey Web browsers) is an add-on that adds a tool bar with a menu of options for debugging and inspecting Web pages. It has a ton of features, my favorite being the View CSS Information option (CSS >> View Style Information, or Control + Shift + Y on Windows) which makes a page element clickable and shows you CSS selectors that affect that particular page element. It’s helpful for exploring and understanding large CSS files and projects that you’re unfamiliar with (such as a new open-source content management system).

It has built-in options for syntax validation for popular Web services, such as W3C’s CSS Validator8 and HiSoftware’s Web Content Accessibility Report9, for your convenience. It has many other useful features, such as disable options for CSS, JavaScript and images, to test for degradation and progressive enhancement; a Forms menu with options for working with Web forms; Display Div Order and Display Block Size options to help you visualize the layout; and so much more.


YSlow - screen shot.10

YSlow11 is a Firefox extension created by Yahoo! developers that integrates with Firebug (therefore you need to have Firebug enabled for it to work). YSlow analyzes a Web page for front-end performance and, in its simplest usage, gives you a letter grade (A being the best and F being the poorest) for each of the best practices for speeding up  your website12.

YSlow also allows you to inspect in detail things that are essential for a high-performance website. For example, the Stats view gives you the total size of a Web page and a summary of items that are loaded when the Web page is requested (i.e. style sheets, JavaScript files, Flash objects and images), so that you can hunt down the bottlenecks that cause a Web page to load slowly.

The Components view outlines every single component of a Web page in tabular format and allows you to inspect it to see attributes such as size, expiration date (for cached files), whether it uses server-side compression (Gzip) and response time (how long the component took to load).

Further Reading

Internet Explorer Web Developer Toolbar

Internet Explorer Web Developer Toolbar - screen shot.17

If you need similar functionality to that of Firebug and Web Developer for Firefox, but want to debug, inspect and tune your Web pages and applications on the Internet Explorer browser, check out the Internet Explorer Web Developer Toolbar18. The IE Web Developer Toolbar, when enabled, opens a toggle-able pane located at the bottom of the Web browser, giving you access to many helpful options for exploring Web page components.

For example, you can experiment to see how page elements work by editing the Web page’s DOM and HTML directly in the browser, allowing you to quickly change and edit DOM elements to see what happens when you perform certain actions or modify certain parts of the code. You can also debug, test and inspect JavaScript with the IE Web Developer Toolbar, giving you options for setting breakpoints, seeing the call stack and exploring variable attributes.

It has a ton of other helpful features, such as selectively disabling IE settings (to see how your Web pages degrade in IE); the ability to view the HTML and CSS source of any Web page with syntax-highlighting; and an in-browser ruler to help you measure things on a Web page.

Further Reading

Fiddler Web Debugger

Fiddler Web Debugger - screen shot.20

Fiddler21 is an Internet Explorer extension that analyzes and profiles a Web page’s HTTP traffic. If you’ve ever wanted to know exactly what happens when a client requests a Web page, Fiddler is the tool that’ll help you do the job. The HTTP Statistics view exposes all components and files required to generate a particular page, giving you details such as the total number of HTTP requests, total page weight, HTTP response headers and cache expiration.

Fiddler permits you to set up breakpoints, allowing you to step through and edit HTTP traffic (to see how it would affect your Web page), a useful feature for analyzing AJAX-based interaction and potential security flaws in a Web application. Perhaps what makes Fiddler so powerful is its extensibility, allowing you to create your own scripts (or import other developers’ scripts) to perform certain tasks or make interface modifications to the extension itself.

Further Reading


DebugBar - screen shot.26

DebugBar27 is a debugging in-browser extension for the Internet Explorer browser. It has many helpful features, such as the ability to send a Web page screenshot via email, a color picker, the ability to view both the original and interpreted code (i.e. if you use JavaScript to manipulate the styles of a DOM object, then you can see the interpreted HTML source code of that manipulation) and a Console API28 (after installing Companion.JS) to help you gain information through a command-line interface about particular components of a Web page.

DebugBar is free for personal and educational use, but you are required to buy a license if you use it for commercial purposes.


HttpWatch - screen shot.29

HttpWatch30 is another HTTP traffic viewer and debugger for Firefox and Internet Explorer that is similar to Fiddler. It has many unique features and a more intuitive, less intimidating interface than Fiddler. Some notable features are the ability to generate request-level time charts (useful for documentation and presentation purposes); decryption of HTTPS31 traffic to help you debug, inspect and tweak your secure SSL-based connections32; and the ability to export captured data to XML and CSV formats for importing into spreadsheet applications such as Microsoft Excel or Google Spreadsheets.

HTTPWatch has a Basic edition, which is free, and a Professional edition, which has more options. Check out the comparison table between the two editions33 to see the exact differences.

Live HTTP Headers

LiveHTTPHeaders - screen shot,34

Live HTTP Headers35 is a Firefox extension that allows you to inspect HTTP request and response headers36. Exploring HTTP headers allows you to debug Web applications, glean some information about the website’s server and inspect cookies sent to the client requesting the page.

For example, the Server response header gives you a website’s HTTP server type (Apache, IIS, nginx, etc.), the HTTP server version and the operating system (though server administrators can remove or limit the information you see for security purposes).

Web Accessibility Toolbar

Web Accessibility Toolbar - screen shot.37

The Web Accessibility Toolbar38 is a freeware extension for Internet Explorer and Opera that gives you a slew of options for quickly evaluating and analyzing your Web content’s accessibility. It has validation options for submitting your URL to content accessibility web services such as Juicy Studio tools39, a grayscale converter to simulate the user experience of individuals with color-blindness and poor eyesight, and a search function for particular page structures (e.g. finding list objects and unordered lists).

Other useful tools released by Vision Australia40 are the Colour Contrast Analyser41, which analyzes the contrast of foreground and background colors for readability, and the Complex Table Mark-Up (or Com Tab) Toolbar42, which can help you understand (and construct) complex tables that are usable by non-traditional Web browsers (such as screen readers).

Further Reading


Fangs - screen shot.45

Fangs46 is an in-browser tool for Firefox that emulates what a screen reader “sees” when visiting a Web page. Its function is simple: to output a transcript of what a screen reader will read out to a user when a Web page is visited. It’s a helpful tool for quickly analyzing if you’ve structured your content effectively so that it’s understandable and usable by vision-impaired individuals, without forcing you to learn to use (and purchase) a screen-reader application such as JAWS47 or Windows Eyes48.

Further Reading

Venkman JavaScript Debugger

Venkman JavaScript Debugger - screen shot51

Venkman52 is the codename for Mozilla’s very own JavaScript debugging environment. It is available as an add-on that can be used to extend browsers such as Firefox, Netscape, and SeaMonkey. It is a robust environment for doing complex JavaScript debugging and troubleshooting. The Console view gives you a command-line interface for interacting with the debugger. It has an excellent Stack view feature that allows you to step through active functions when it reaches breakpoints.

Further Reading


ColorZilla - screen shot.56

ColorZilla57 is an incredibly simple — but very useful — extension for Firefox. If you’ve ever wanted to determine what colors are used on a Web page, ColorZilla is the tool for the job. It adds an eyedropper icon to the bottom-left corner of Firefox.

Clicking on the eyedropper icon makes objects on the Web page clickable, and upon clicking a particular section of a Web page, it outputs the hexadecimal, RGB and hue/saturation values of that area . Before ColorZilla, you might have pasted a screen capture of a Web page into a graphics editor like Photoshop and then used the eyedropper tool in the editor to sample colors. ColorZilla saves you time and streamlines color-sampling processes.


FireShot - screen shot.58

FireShot59 is an in-browser tool for Firefox and Internet Explorer that allows you to take screenshots and then annotate, edit, organize and export them. Screen-grabbing is a common activity for Web developers to document previews of Web application prototypes and share them with clients, and FireShot gives you a feature-packed in-browser option to manage and streamline your screenshot needs.

Web Inspector

Web Inspector - screen shot.60

Web Inspector61 is part of the Webkit open-source browser engine project62. It’s an ultra-sleek tool for inspecting the DOM hierarchy in a separate, compact HUD-style window. You can easily search the DOM, explore the DOM tree (hierarchy) and have a useful interface for isolating DOM sub-trees and nodes so that you can focus on particular sections of a Web page. The Web Inspector also provides you with a Style pane to explore CSS rules applied to particular page elements.


FireFTP - screen shot.63

FireFTP64 is a free, cross-platform Firefox extension for FTP’ing files. It offers several advantages to stand-alone FTP applications, such as its operating system-independent requirements. What’s exceptional about FireFTP is that even though it is an in-browser (and free!) application, it has all the features you would expect from a standalone FTP application, such as support for secure (SSL, TLS, SFTP) protocols, a synchronization feature to sync up local and remote files, and directory comparison to help you see what files are missing or different between two directories and much more.

What’s your favorite in-browser tool?

There is an overwhelming amount of in-browser tools for Web development out there. Some are specific to particular Web technologies and set-ups (such as FirePHP65 for PHP developers, SQLite Manager66 for developers using SQLite databases, and Opera Dragonfly67 for developers who prefer using the Opera browser). If your favorite tool isn’t on the list, let us know in the comments section why it’s your favorite and why we should check it out.



  1. 1 http://getfirebug.com/
  2. 2 http://getfirebug.com/
  3. 3 http://www.ibm.com/developerworks/web/library/wa-aj-firebug/
  4. 4 http://alternateidea.com/blog/articles/2006/05/12/an-in-depth-look-at-the-future-of-javascript-debugging-with-firebug
  5. 5 http://www.webmonkey.com/tutorial/Build_Better_Pages_With_Firebug
  6. 6 http://chrispederick.com/work/web-developer/
  7. 7 http://chrispederick.com/work/web-developer/
  8. 8 http://jigsaw.w3.org/css-validator/
  9. 9 http://www.cynthiasays.com/
  10. 10 http://developer.yahoo.com/yslow/
  11. 11 http://developer.yahoo.com/yslow/
  12. 12 http://developer.yahoo.com/performance/rules.html
  13. 13 http://yuiblog.com/blog/2006/11/28/performance-research-part-1/
  14. 14 http://yuiblog.com/blog/2007/04/11/performance-research-part-4/
  15. 15 http://www.ibm.com/developerworks/web/library/wa-aj-perform/?ca=dgr-lnxw01FasterAjax
  16. 16 http://www.codinghorror.com/blog/archives/000932.html
  17. 17 http://www.microsoft.com/downloads/details.aspx?familyid=e59c3964-672d-4511-bb3e-2d5e1db91038&displaylang=en
  18. 18 http://www.microsoft.com/downloads/details.aspx?familyid=e59c3964-672d-4511-bb3e-2d5e1db91038&displaylang=en
  19. 19 http://www.15seconds.com/issue/070208.htm
  20. 20 http://www.fiddlertool.com/fiddler/
  21. 21 http://www.fiddlertool.com/fiddler/
  22. 22 http://msdn.microsoft.com/en-us/library/bb250446.aspx
  23. 23 http://www.fiddlertool.com/Fiddler/help/ui.asp
  24. 24 http://www.fiddlertool.com/Fiddler/help/video/default.asp
  25. 25 http://www.west-wind.com/WebLog/posts/4085.aspx
  26. 26 http://www.debugbar.com/
  27. 27 http://www.debugbar.com/
  28. 28 http://www.my-debugbar.com/wiki/CompanionJS/ConsoleAPI
  29. 29 http://www.httpwatch.com/
  30. 30 http://www.httpwatch.com/
  31. 31 http://en.wikipedia.org/wiki/Https
  32. 32 http://en.wikipedia.org/wiki/Secure_Sockets_Layer
  33. 33 http://www.httpwatch.com/editions.htm
  34. 34 http://livehttpheaders.mozdev.org/
  35. 35 http://livehttpheaders.mozdev.org/
  36. 36 http://en.wikipedia.org/wiki/List_of_HTTP_headers
  37. 37 http://www.visionaustralia.org.au/ais/toolbar/
  38. 38 http://www.visionaustralia.org.au/ais/toolbar/
  39. 39 http://juicystudio.com/services.php
  40. 40 http://www.visionaustralia.org.au/info.aspx?page=674
  41. 41 http://www.visionaustralia.org.au/info.aspx?page=628
  42. 42 http://www.visionaustralia.org.au/info.aspx?page=1812
  43. 43 http://www.webaim.org/articles/ais/
  44. 44 http://www.visionaustralia.org.au/toolbar/1.2/versions/en/documentation/WCAG_checklist.html
  45. 45 http://www.standards-schmandards.com/index.php?show/fangs
  46. 46 http://www.standards-schmandards.com/index.php?show/fangs
  47. 47 http://www.freedomscientific.com/fs_products/software_jaws.asp
  48. 48 http://www.gwmicro.com/Window-Eyes/
  49. 49 http://www.standards-schmandards.com/2007/rapid-accessibility-feedback/
  50. 50 http://www.standards-schmandards.com/2007/search-guidelines/
  51. 51 http://www.mozilla.org/projects/venkman/
  52. 52 http://www.mozilla.org/projects/venkman/
  53. 53 http://www.mozilla.org/projects/venkman/venkman-walkthrough.html
  54. 54 http://www.webreference.com/programming/javascript/venkman/
  55. 55 http://www.hacksrus.com/~ginda/venkman/faq/venkman-faq.html
  56. 56 http://www.colorzilla.com/firefox/
  57. 57 http://www.colorzilla.com/firefox/
  58. 58 http://screenshot-program.com/fireshot/
  59. 59 http://screenshot-program.com/fireshot/
  60. 60 http://webkit.org/blog/41/
  61. 61 http://webkit.org/blog/41/
  62. 62 http://webkit.org/
  63. 63 http://fireftp.mozdev.org/
  64. 64 http://fireftp.mozdev.org/
  65. 65 http://www.firephp.org/
  66. 66 http://code.google.com/p/sqlite-manager/
  67. 67 http://www.opera.com/products/dragonfly/

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Jacob Gube is the Founder and Chief Editor of Six Revisions, a web publication for web developers and designers, and the Deputy Editor of Design Instruct, a web magazine for designers and digital artists. He has over seven years of experience as professional web developer and web designer and has written a book on JavaScript.

  1. 1

    Awesome list. Thanks guys :)

  2. 52

    Scrapbook is also an amazing extension to capture html pages (better than “save a”s)

  3. 103

    Firebug is without a doubt the most used developer tool that I have installed. I would sacrifice my text editor of choice (with syntax highlighting and tabs etc) for notepad just to use Firebug. Web developer is then second for me as its provides a large range of options. Also Show IP is useful for me as it allows me quickly see what server I am working on when on a development or staging server.

  4. 154

    Dummy Lipsum is a very handy little Firefox extension. It does just one thing, but the one thing it does is extremely handy if you’re developing an application with a lot of forms. It simply allows you to right click on a text accepting element (a textarea, line input control, etc) and populate it with Lorem Ipsum text. When you’re testing a web app and need to repeatedly fill in the same form over and over again I can’t tell you just how much time this little plugin saves!

  5. 205

    Cool nice! I use Firebug and Web Developer also. :)


  6. 256

    my favorite tools in G Chrome browser , reaaaally cool things only for debugging but not a good browser.

  7. 307

    I like the fire bug!

  8. 358

    Don’t forget about the XRAY Bookmarklet… it’s fairly limited, but a good option for debugging IE6.


  9. 409

    Erm, the url you posted to webkit is from 2006… Its 2008 now. thats a 2 years old article…

    I suggest you link to this post instead: http://webkit.org/blog/197/web-inspector-redesign/

  10. 460

    You forgot Dust-Me Selectors, IE Tab and Mozilla Accessibility Extension. But my favourite has to be Firebug. I can’t even remember what it was like before Firebug.

  11. 511

    Definitely Firebug.

  12. 562

    I also use HTML tidy, which has a plugin for Firefox. It provides you with a simple view of validation errors and also gives a more detailed view of the exact problem on each line. There are other tools that do the same things, but I just find it really useful: http://users.skynet.be/mgueury/mozilla/

  13. 613

    Tamper Data is a little bit more powerful than Live HTTP Headers.

  14. 664

    Is there anything out there where you can edit the CSS of a website in IE7 and IE6? Just like you can with the web developer extension in Firefox??

  15. 715

    I would definitely say FIREBUG!
    I am sure it has saved me 500h+ of developing time!

  16. 766

    very handy for every webdeveloper: the w3c validator plugin for firefox!

  17. 817

    Firebug, FireFTP are essential to how I work. I used to use Web Developer Toolbar a lot, but that’s changed since Firefox 3 went and broke the keyboard shortcuts :-(

  18. 868

    Another mention should go to ScreenGrab. I frankly cannot live without it. Invaluable for sending whole page screen shots of a site that is being designed/developed.

    Not a truly web developer based plugin – I found using Pencil to be very useful for mocking up forms and dialogs. At the very least you don’t need any image manipulation apps – just Firefox.

  19. 919

    FireFTP, ColorZilla, MeasureIt, Firebug, Webdeveloper extension

    I code websites just using Firefox and Notepad++, all freeware and a lot handier than all those heavy, expensive wysiwyg web-editors

  20. 970

    FireBug and Web Developer and screengrab (good for making fast screenshot) and iMacro

  21. 1021

    I use Web Developer :D
    Great list by the way ;)

  22. 1072

    I like httpfox. It is similiar to httpwatch but it is a free addon for FireFox.

  23. 1123

    Xray is indispensable:

    It’s a bookmarklet that, when activated, describes any element you click on. Awesome!

  24. 1174

    Web developer, any day

  25. 1225

    My favorite is firebux :X

  26. 1276

    Man, seriously, enable the function to make small posts in RSS

  27. 1327

    Good list, the few firefox addons that I’d add that weren’t included in the list are:
    HTML Tidy
    Obtrusive javascript checker

  28. 1378

    Installed FireShot and ColorZilla after reading this article, thanks!!!

  29. 1429

    Nice article,

    Tamper Data for Firefox and TamperIE for Internet Explorer.

  30. 1480

    Been well into firebug for a while… recently got into using FirePHP. Its awesome for php developers, especially php developers wanting to debug their ajax (or ajajson) applications.

  31. 1531

    Three words: “Colour Contrast Analyser

    Not sure if this has been mentioned yet but, if everyone used this when choosing their colour schemes the web would be a better place.

    The tool allows me to check and compare foreground and background colour contrast inline with checkpoint 1.1 of the WCAG v1.0.

    If someone was to integrate this into a nice, easy to use, Firefox Add-on it would be awesome!

  32. 1582

    You can easily add pixel perfect to firebug :

    “Pixel Perfect is a firefox firebug extension that allows web developers to easily overlay a web composition over top of the developed html. Switching the composition on and off allows the developer to see how many pixels they are off while in development.”

  33. 1633

    These are great, I thought I knew about all the good ones but apparently not. Like debug mode in Safari/Webkit, there’s also a lot of other great tools that come on every Mac that I take advantage of. I didn’t know Webkit had a debug mode that was different than Safari, I’ll be checking that out this morning.

  34. 1684

    Nice list, thanks for sharing.
    I would add URLParams

  35. 1735

    Thank you very much for this!

  36. 1786

    Firebug allows me to edit the CSS and HTLM and see the changes instantly.

    Can Web developer do that? I have not seen the ability to edit the CSS directly in browser with Web Developer or IE Developer.

    IF anyone knows how please tell me. Thanks!

  37. 1837

    I use Firebug, web developer toolbar, fiddler, liveHttp headers, fireFTP. I would try to use other tools mentioned in here as well.

  38. 1888

    If you are familiar with Firebug and love its features then the IE Developer Toolbar is a big let-down. You can’t manipulate the DOM or HTML, it does not improve error messages (wish it did!) and it doesn’t give you load times.

    Firebug is much, much better. IE is a slacker…

  39. 1939

    @Justin Web Developer lets you edit CSS and HTML on the fly as well. Load the toolbar and the options will be included in the CSS drop down and the MISC dropdown. CTRL + Shift + E for the CSS

    I used alot of the plugins mentioned but can’t live without Web Developer or FireFTP. Also along with FireShot, ScreenGrab! is a must have.

    Great list!

  40. 1990

    I use WebDeveloper, Firebug and Colour Contrast Analyzer

  41. 2041

    I’d like to add CSSViewer, HttpFox and Screen grab! to the list.

    CSSViewer: Activate it with a button, hover over your website and get the resulting CSS for the specific element in a layover. Great, because it is fast (at least faster than activating Firebug/WebDeveloper)!

    HttpFox: Fiddler in Firefox

    Screen grab!: Another great screenshot tool for a quick shot…

  42. 2092

    This is a great post, and I either have used most of these or currently use them. My set up right now is: Web Developer, Firebug, Colorzilla. They are all amazingly useful, However i am still missing one part that I would like to find, Is there any way to fully integrate the web development into the browser: I.E.: edit and upload all from Firefox, so i can minimize the alt + tabbing? I will implement the FireFTP for the upload part, but is there a solution similar to firebug that will allow me to edit the files from Firefox as well?

  43. 2143

    IE Web Developer Toolbar is a little hokey compared to firebug. Firebug Lite can be be used to view page elements in a more “Firebuggy” style. Its basically a javascript include that you drop into your page. Not the greatest solution but definitely better. Or you could just forgot about IE altogether :)

  44. 2194

    Great list. I’m already using most of these tools, and will definitely try out the others here. Firebug,Web Developer, Yslow, and Fire FTP have changed the way work dramatically

  45. 2245

    Great list! With all the lists out there this one stood out for me and actually introduced me to something new and useful to my set-up.


  46. 2296

    Very cool post. Thanks for the info.

    I’ve been using Blackbird. It’s a neat javascript widget you can include on your page to send console messages to during development and it works on most browsers.


  47. 2347

    excellent collection. I use FireBug, but didn’t know about YSlow. Will definitely be give it a try. Dugg.

  48. 2398

    @Gabe Diaz – Thanks Gabe. I just started playing around, but I find it is not as easy to use as firebug. I could not select the individual cell with the inspector and then edit the css in the same window. It’s in two seperate windows. I would have to search for the tag and edit.

    Firebug rules all. I just wish IE Developer would allow me to edit the CSS to help my browser testing. God how can they suck so hard when there are so many good examples of how to do things.


  49. 2449

    My favourite development tools for firefox are:
    HTML Validator
    IE Tab
    and finally Web Developer Toolbar

  50. 2500

    I think Opera Dragonfly should be listed at the top of this list. It’s much more better than Firebug.


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