The W3 Consortium has its own online validator which you can use for free.
It may be found at: A CSS validator checks your Cascading Style Sheet in the same manner.
In particular, an HTML validator checks to make sure the HTML code on your web page complies with the standards set by the W3 Consortium, the organisation ("organization" in US English) that issues the HTML standards.
There are various types of HTML validators: some only check for errors, while others also make suggestions about your code, telling you when it might lead to (say) unexpected results.
Again, you can get free validation for your style sheets from the W3 Consortium: There are numerous other validators around, both free and commercial, focusing on different aspects of your web page.
You can find a list of free ones (including specialised validators like those that check your code for accessibility) from the Free HTML Validators, CSS Validators, Accessibility Validators page at There are a number of reasons why you should validate your page.
I try to validate my pages each time I make modifications, although I must admit that I sometimes forget to do so (with the occasional disastrous consequence; Murphy's Law doesn't spare webmasters).
I find that having an offline validator helps to make sure that I remember to validate: having to go online just to validate my pages tends to make me put off validation till later, with the result that it'll occasionally get overlooked.
Some people validate every time they make a modification to their pages on the grounds that careless mistakes can occur any time.Even if you are not familiar with HTML and CSS, there are still some ways you can deal with the errors that you discover from validating your page.This article can be found at https:// Copyright 2003-2016 by Christopher Heng. Get more free tips and articles like this, on web design, promotion, revenue and scripting, from https:// You can learn of new articles and scripts that are published on by subscribing to the RSS feed.Depending on the complexity of your code, you may even want to test it with different browsers to make sure that your site looks the same in all of them, since it's possible that you are using features of HTML and CSS that are only implemented in some browsers but not others.If you have designed your site using a visual web editor, and are not familiar with HTML and CSS, you will face an additional problem.
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If you are wondering what the difference is, an analogy from normal human language will hopefully make it clear.