Alpine HTML Doctor
- Identifies common HTML code errors, corrects the code, and generates a repair file for cut and paste back into a document.
- http://www.alpineinternet.com/.docs/pg/11133

Pure PHP XHTML Validator
- PHP class for validating XHTML documents. Source code available under LGPL.
- http://www.bermi.org/xhtml_validator

Validator-Lite
- Offers validator for HTML, XHTML, and DTD-based XML languages.
- http://www.webthing.com/software/validator-lite/

Total Validator
- Validator for WAI, XHTML, and HTML. Also checks for broken links and spelling mistakes.
- http://www.totalvalidator.com/

Markup.co.nz
- Validator which attempts to load XHTML document in the MSXML parser and generate an error report. Online and Download versions.
- http://markup.co.nz/validate/validateHome.htm

HTML Code Cleanup
- Validator and hand cleanup by professionals.
- http://www.htmlcodecleanup.com/

HTML/XML Validator
- Validates and repairs HTML, XHTML, and XML. Also includes accessibility checking.
- http://validator.aborla.net/

Web Validators
- Links to validators for XHTML, HTML, CSS, RSS, XML, and RDF documents.
- http://validator.czweb.org/

Microsoft Word 2000 HTML Mess Cleaner
- Removes clutter from Microsoft Word 2000-generated HTML. ASP source code available for purchase.
- http://www.algotech.dk/word-html-cleaner-input.htm

HTML Tidy Download
- HTML Tidy plugin. Fixes HTML and XHTML, converts HTML to XHTML.
- http://chami.com/html-kit/tidy/

Validome Markup Validation Service
- Multilingual validator for HTML, XHTML, and XML.
- http://www.validome.org/

Walidator
- Portal to several validators and URL analyzers.
- http://www.walidator.com/

Validation Bookmarklets
- Javascript bookmarklets which check alt text, broken images, small screen readability, and HTML validity.
- http://www.squarefree.com/bookmarklets/validation.html

HTML and XHTML Syntax Checker
- Locates webpage coding errors, lists error number and page source.
- http://htmlvalidator.com/lite/onlineval.php

HTML Tidy Online
- Cleans up coding errors, especially useful for deeply nested ones.
- http://infohound.net/tidy/

Dr. Watson
- Checks HTML code, links, spelling, download time and link popularity.
- http://watson.addy.com/

Web Page Backward Compatibility Viewer
- Uncheck tags to be unsupported and see how the page looks.
- http://www.delorie.com/web/wpbcv.html

Web Page Purifier
- Check how a webpage looks with different HTML versions.
- http://www.delorie.com/web/purify.html

Web Mechanic
- Validator and lint eliminates redundant or conflicting tags and compresses image files. Pay service.
- http://www.webmechanic.com.au/

W3C HTML Validation Service
- World Wide Web Consortium validator.
- http://validator.w3.org/