Validation programs can help you wade through some rather murky waters. For example, is it better to have a web page that perfectly follows the official HTML language standard or one that perfectly supports the browsers used by your page's visitors? Unfortunately, it is almost impossible to do both.

When you consider that the visitors will be using one of about a dozen popular browser versions, things get really ugly.
These programs will help you see what problems you have, either with the standards or with a particular browser.

Then there are programs that verify that all of the links on your page still lead somewhere. If you link to other sites, those URL's may have changed or the site may have gone away entirely. You can even run into trouble with links to other pages on your own site due to mistyping or renaming.
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Cascading Style Sheet Validators

Jigsaw Powered
Enter the URL of the document (either HTML with CSS, or CSS only):


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HTML Validators

w3c HTML Validation Service
Enter the URL of the web page to be validated:

Show source input Show an outline of this document
Show parse tree Exclude attributes from the parse tree

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Accessibility Validators