I’ve spoken about the virtues of clean, semantic, valid markup before, and lots of designers recommend that you validate your code. What doesn’t seem to get addressed, however, is how one goes about validating the HTML of a web page.

A Major Hassle

It used to be that you would have to validate pages one by one using the W3C’s free validator tool. This method works, but it sure can be time consuming, especially if you have a large site or a site that is mostly valid already. Getting through a lot of pages or finding the few that have problems is very difficult this way.

Validation on the Fly

Luckily, Marc Gueury decided to do something about this important but difficult process. He wrote an HTML Validator Extension for Firefox. It’s based on HTML Tidy—basically, you install a validator in your browser.

The validator extension for Firefox is great because all you have to do is browse from page to page to see which are valid and which are not—an icon in the corner of your browser tells you whether your page is valid, contains warnings, or contains one of two kinds of errors (errors that the extension knows how to fix and errors that it doesn’t). To see the warnings and errors, you simply need to view your page source. This all takes place on your machine, so there is no external server to fiddle with or wait for.

Accessibility Evaluation, Too

The HTML Validator extension also has accessibility evaluation built in—if you want to see how accessible your site is, you can turn on evaluation for one of 4 different levels. This part of the tool is helpful for a quick look at how accessible your site is.

Not Quite Perfect, But Close Enough

The validator extension isn’t quite perfect—occasionally it will make mistakes (especially with heavily nested elements) and it seems a little bit “touchy” at times, but for the most part it is a powerful and convenient way to validate your website. I used it to make my site valid, and I wasn’t even sure I was going to validate it at all before I found the HTML Validator extension.