I am after a HTML validation tool for Firefox to run locally on my development machine.

I have tried Total Validator. But it’s crazy, it keeps telling me to upgrade, I have done that several times.

I am using the Web Developer extension. The local CSS validation works fine, but the local HTML validation hangs.

Can someone recommend another one?


2 Answers 2


I have HTML Validator installed. It does a pretty good job, a simple icon in the toolbar will tell you when something is off:

enter image description here

If you click the icon you get the source code with a list of errors:

enter image description here

I use it to validate pages locally before uploading them.

  • I just installed it, no drama , no fuss. It works. Jul 19, 2015 at 11:09
  • 1
    I'm using this for years (Jan beat me with his answer, else I had recommended it). So: thumbs up for this!
    – Izzy
    Jul 19, 2015 at 12:12

If you would like to invest some time and disk space the definitive validator is the W3C online validator.

You can however also download a snapshot of the validator and run it yourself offline, you will need an instance of Apache Web server, Perl, some Perl libraries and the validator itself.

This guide explains how to install and run your own validator instance on Windows. For other platforms the installation guide gives details.

All the above is available Free, Gratis and Open Source - you are encouraged to feed back any bugs you spot and you are obliged by the GPL licence to give back any bug fixes and/or enhancements that you might make.

As an example I ran this page through the W3C validator and it came up with the following report:

enter image description here

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