In Firefox, theres a Extension called “Html Validator”. It adds a little indicator icon at the bottom right corner of your window. When a page you visit isnt valid, it lights up. You can click on it to see the errors. The really important feature of this extension is that it does not make a connection to w3cs validator. The same validating SGML parser used by w3c is bundled. This means, it validate any local html files. (this is most important use for me, as i do web dev with manually coded html files. Each time i preview my html in browser, i can also know whether it has html errors.)

Is there anything similar in Google Chrome, Opera, Safari, or even IE9? As far as i checked in the past years, all other validator ive seen simply send the current url to w3cs validator site.

There is a new HTML validator available for Chrome. It uses a JavaScript port of LibTidy and thus validates locally without the need of remote services.

I dont think that type of thing is usually built in, because they arent needed by the average user and can slow down your browsing. Generally speaking, add-ons are the way to go, in my humble opinion.

The top two browser additions for anyone who is developing any website are: Firebug (as mentioned by a previous response) and the Web Developer toolbar, available for many browsers. Here is a link to the developers page for the toolbar: Website for Web Developer Toolbar

The Web Developer Toolbar on the other hand, allows you to Validate HTML, CSS, etc, either on a local host, or on the web, turn off Javascript, turn off CSS, plus much more!

The HTML Tidy Browser Extension works quite well, although it doesnt have as many features as the Firefox counterpart. As an added bonus, it works on localhost pages. You can get it here: https://chrome.google.com/webstore/detail/html-tidy-browser-extensi/gljdonhfjnfdklljmfaabfpjlonflfnm

HTML Validator by Robert Nyman for Google Chrome has an indicator icon, displays inline results, and validates local files.

google chrome has a property inspector if you right click and select inspect element. If you go to resources, and navigate to the file you would like to validate, some files display any errors on the page, I know that javascript does.

Every browser have an HTML validator. If you re using Mozilla Firefox, then you can install a plugin called "Fire bug", through which you could see the ajax and jquery calls to server. its missing in many of other broswers....

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