My favorite Rated 5 out of 5 stars

For a long time there was a warning about the particular w3c API being deprecated, and now it no longer works at all.

Edit: dev fixed and made new release very quickly. 5 stars now.

This has been my long time favorite, especially when developing internal websites that the w3c validator cannot read directly. It's light and fast. What more could one want?


Thanks for the feedback, I look at it...

(Update) Please use version 0.962 that you can find here:

! Not Local ! Rated 3 out of 5 stars

Works well - however be aware that validation IS NOT taking place locally.

A request containing page data is sent to W3C and can be observed when inspecting traffic (eg in fiddler). A big no no for secure environements.

Not ready for it Rated 3 out of 5 stars

I don't feel it as my tool. I'm used to check errors online and there I can see all the messages in proper way. Here they are listed at the bottom and can't see all of them, yes there is a plus because when you click on a error/warning it shows you tha exact place of it but I can't say I got used to using it yet.

Helpful Rated 5 out of 5 stars

Even if you don't rely on its entire functionality and windows, it's good because this extension shows you if your page is correct or not. You are aware of all the errors/warnings during coding so the result would be - better code writing and developing the skills and knowledge.

Useful Rated 5 out of 5 stars

I use it every day. I like it, because if you forgot something you would find out what would be the mistake. That way you learn to code more efficient and probably won't need validator in the future. Another positive thing is that you can check either through the extension or use both online validators by passing the current page to them.

Rated 5 out of 5 stars

It comes in great help for beginners in web developing.

Great tool Rated 5 out of 5 stars

We can work more efficient using this checker.

Rated 5 out of 5 stars

Very helpful HTML validator. I recommend to disable checking HTML for all pages to speed-up Firefox. You can check it in the code view (Ctrl + U).

"Firefox 30 hangs" fix found Rated 5 out of 5 stars

Problem in the Firefox profile, subdir \tidy which contains the file 'spvalid.err'. Normally this file is zero bytes, with no data. The file had been 'restored' from another PC running a different o/s. Removed subdir \tidy, then re-installated Add-in which has repaired the issues and HTML Validator is now running as anticipated. Thanks to Marc for hint about Firefox profile.

This user has a previous review of this add-on.

Don't appear on Add-on Bar Rated 4 out of 5 stars

I'ts a great tool. But, I have Firefox 29 and the icon don't appear on Add-on Bar.

Firefox 29

Thanks for the feedback. You are the fisrt person to complain about it. And seen Firefox 29 is new. I would like to solve your problem asap. I have Firefox 29 on my machine but no issue.

Please do this:
- Click on the new menu toolbar of Firefox 29.
- At the bottom, click customize. Do you see the HTML Validator icon there ?
If yes, drag and drop it on the toolbar where it was.

- if not, right click on an empty space in the toolbar and click "customize..."
- the same list should show.

Whatever is the result, good or bad. Can you send me the result to my email "" ?
- please add the OS and OS version
- the version from which you upgraded or after which change that
the problem happened.
- also if possible screenshot of the issue if it is still there.


Rated 5 out of 5 stars

My son likes this. Says he can do his job better with it.

Rated 4 out of 5 stars

As far as I know, it's the only add-on of its kind. Its automatic validation approach allows to detect that elusive unclosed tag that only shows up when you've loaded certain data (thus goes unnoticed with manual validation). Definitively, a must-have for webmasters.

The only major drawback is that it doesn't support HTML5 (it only provides a link to submit code to an online validator and such feature is provided by other extensions that do it better).

BTW, make sure you only use it on your own sites. There's no point in wasting memory and CPU cycles validating HTML at Google or Yahoo.

great but it hangs on different sites Rated 4 out of 5 stars

very often it hangs on different sites, so i close the FF with the Taskmanager. I cant say what site it is, one time it goes, other time it hangs

Make Firefox stop following clicked links... Rated 3 out of 5 stars

When I enable this addon, after several minutes Firefox stop to follow clicked links... I must close FF. However it still run in background and I must close it "really" via Task manager. No more problem when I remove the addon.


Can you mail me ? It would be interesting to know after which website visit that this is happening. There is a diagnostics logging to find this out. This is very probably related to Firefox bug


Rated 5 out of 5 stars


Excellent Rated 5 out of 5 stars

Fabulous tool. It's the biggest reason for my continued usage of Firefox.

This review is for a previous version of the add-on ( 

ok when it works Rated 3 out of 5 stars

But it lags to computer bad after a while, and sometimes just goes into a jquery error loop making the computer unusable unless firefox is close and the computer is rebooted, This is on a vista with firefox 23.0.

This review is for a previous version of the add-on ( 

Need more info

I am not sure of your issue. There are nearly no such issue reported since years about the extension. Except this firefox bug:

The extension contains a work-around to try to avoid it.

Also note, you need version 0.957 for FF 23.

I would be pleased that you send me a mail explaining what you see, what you found. (


Rated 4 out of 5 stars

Firefox 23.0 update causes a problem. The application claims "not in domain list". This can be circumvented by invoking the page source, but that means an unnecessary extra step.

This review is for a previous version of the add-on ( 

FF 23

Thanks for the problem report. It is a FF23 issue only.

A new version 0.957 will be available at home page tonight (14 august 2013).

Then it will take some weeks to be approved and published in this site.

Very helpful Rated 5 out of 5 stars

Very helpful and easy to use. Good results and advices are retrieved.

This review is for a previous version of the add-on ( 

Useful! Rated 5 out of 5 stars

Very handy to have in the view-source!

This review is for a previous version of the add-on (