HTML Validators

W3C HTML Validation Service

Validate by typing in an URL or uploading a file.

Checky

Document validation and analysis Extension for Firefox, Mozilla and Netscape.

HTML Tidy

Dave Raggett's HTML TIDY is a free utility that can clean up code into nicely layed out markup. Tidy is able to fix up a wide range of problems and to bring to your attention things that you need to work on yourself. It is available in binaries and source for many platforms.

Web Page Purifier

Allows authors to view a page purified to be compliant with various versions of HTML.

WDG HTML Validator

Enter the URL of an HTML document to validate.

Tidy your HTML

This is an online version of Tidy at the W3C.

Web Page Backward Compatibility Viewer

Enter an URL and a browser and see what your page looks like in older versions.

Meta Tag Analyzer

This online tool will analyze your title tag, keyword meta tag, and description tag for proper construction and length.