HTML Validation Service
Online code validation service through the World Wide Web Consortium, the body that recommends and sanctions web standards. Submit your web address for a real-time code validation report of your HTML or XHTML document.

HTML Tidy
Utility for cleaning up HTML code and fixing common mistakes. Particularly useful for revising older hand-coded pages and sloppy HTML produced by older WYSIWYG editors. Free to download for Windows, Macintosh, and a variety of other operating systems, or submit your web address for real-time code cleanup.

DMX Tidy
Free Dreamweaver MX extension to clean up old documents, based on the open-source Tidy application listed above. This extension is much more comprehensive and useful than Dreamweaver's internal Clean Up HTML function.

CSS Validator
Online code validation service through the World Wide Web Consortium, the body that recommends and sanctions web standards. Submit your web address for a real-time code validation report of your CSS file.

Microsoft Office HTML Filter
MS Office applications (Word, Excel, etc.) include a lot of proprietary code for round-trip editing between Office and the Web. If you are simply exporting your Office documents to a web page and will no longer be editing them in Office, use this Microsoft-supplied filter to strip out this nonstandard code.

HTML Validator
This program runs on Windows-based systems and enables web developers to validate their code locally without the need to submit a web address to a web-based validation service. Available as either a full-featured professional program for purchase or an HTML Validator Lite version for free download.