Stop the press! Found an amazingly useful extension, thanks to Andy Jarrett – a HTML validator based on Tidy that runs in your Firefox status bar, giving you a count of errors and warnings on the current page.

Now, even if I don’t bother to validate my pages, that little status bar will bug me anywhere it doesn’t show me a little green tick. Damn that’s useful! I got all the developers in the office to install it yesterday, it will improve my productivity a heap by automating my nagging. I’m excited! If you double-click on the status bar score it opens up a source view window with the errors and warnings highlighted, and even has a little explanation window down the bottom. It can also attempt to fix the problems for you, and presents before-and-after html source and browser views.

The only caveat is how Tidy classifies errors and warnings – anything that it can correct automatically is a warning, anything that completely mystifies it is an error. So, a missing DOCYTPE declaration or an invalid attribute is just a warning – Tidy says “hey, no problem, I’ll just fix that right up for you” – whereas the W3C validator would get all medieval on yo’ ass over the same issues. I guess it’s a case of not being happy with a page until there’s a little green tick in the bottom of your screen.

Cos it runs in your own browser, it works behind firewalls, on pages requiring authentication, etc.

Check it out for yourselves – HTML Validator for Firefox and Mozilla.