About the W3C HTML Validation Service

This service checks HTML documents for conformance to W3C HTML and XHTML Recommendations and other HTML standards. Related resources include:

• Source code availability.
• The to-do list for the service.
• DTDs (document types) supported by this service (the SGML catalog).
• The www-validator mailing list.
• How to provide feedback.

Other resources

Documentation/specifications:

• W3C's HTML home page.
• The HTML 4.01 specification.
• XHTML 1.0: The Extensible HyperText Markup Language.
• XHTML 1.1: Module-based XHTML.

Online tools/validators:

• The WDG HTML validator is another excellent online validation service.
• A Real Validator is a shareware HTML syntax checker for Windows systems, from the author of the WDG validator.
• Site Valet by Nick Kew is a comprehensive set of tools for checking and monitoring your web sites.
• Clean up your HTML using HTML tidy (or use Site Valet's web interface to tidy.)
• Validate your CSS using the W3C CSS Validation Service.
• Validate your RDF using the W3C RDF Validation Service.
• Validate your XML Schema documents using the W3C XML Schema Validator.

Credits

This service uses:

• James Clark's excellent SGML parser.
• The LWP Perl Modules by Gisle Aas and Martijn Koster for retrieving documents.
• SGML error explanations originally written by Scott Bigham.
• Open source software including Apache, Perl, and Debian GNU/Linux.
• Patches and ideas from:
  • Terje Bless
  • Liam Quinn