Bobby - W3C's web content accessibility guidelines checker. Helps ensure that the page is accessible to all regardless of disability.

W3C HTML Validation Service -  World Wide Web Consortium validator.

NetMechanic - HTML validator and lint, link testing, load time calculations, image size reduction, and server performance monitoring.

Doctor HTML - Lint checks spelling, images, links, and more.

WDG HTML Validator - Gives very easy to read HTML error messages. Can validate one page or a batch of pages at one time.

Web Page Backward Compatibility Viewer - Uncheck tags to be unsupported and see how the page looks.

Web Site Garage - HTML lint, GIF checker, traffic analyzer.

Web Page Purifier - Check how a webpage looks with different HTML versions.

Dr. Watson - Checks HTML code, links, spelling, download time and link popularity.

CYAN - Web interface to validator HTML Tidy. Fixes HTML and XHTML. Converts HTML to XHTML.

Search Engine World Validator - HTML and XHTML validator. Validates by URL and file upload.

Alpine HTML Doctor - Identifies common HTML code errors, corrects the code, and generates a repair file for cut and paste back into a document.

Web Mechanic - Validator and lint eliminates redundant or conflicting tags and compresses image files. Pay service.

HTML Code Cleaner  Lint reduces size of HTML files by removing unnecessary tags and spaces.

Link Validator Add On For Webpages - Offers a copy and paste link checker JavaScript code to create the link checker file. Then, there is a simple copy and paste script reference code to this JavaScript file to be placed on an HTML webpage. Bad URL's will be color coded according to type of error. For use with Internet Explorer.