About The W3C Markup Validation Service

Table of contents

    1. About this service
    2. Other resources
    3. Credits

About this service

   The Markup Validator is a free service by W3C that helps check the
   validity of Web documents.

   Most Web documents are written using markup languages, such as HTML or
   XHTML. These languages are defined by technical specifications, which
   usually include a machine-readable formal grammar (and vocabulary). The
   act of checking a document against these constraints is called
   validation, and this is what the Markup Validator does.

   Validating Web documents is an important step which can dramatically
   help improving and ensuring their quality, and it can save a lot of
   time and money (read more on why validating matters). Validation is,
   however, neither a full quality check, nor is it strictly equivalent to
   checking for conformance to the specification.

   This validator can process documents written in most markup languages.
   Supported document types include the HTML (through HTML 4.01) and XHTML
   (1.0 and 1.1) family, MathML, SMIL and SVG (1.0 and 1.1, including the
   mobile profiles). The Markup Validator can also validate Web documents
   written with an SGML or XML DTD, provided they use a proper document
   type declaration.

   This validator is also "An HTML validating system conforming to
   International Standard ISO/IEC 15445—HyperText Markup Language, and
   International Standard ISO 8879—Standard Generalized Markup Language
   (SGML)" – which basically means that in addition to W3C
   recommendations, it can validate according to these ISO standards.

   Related resources include:
     * The Documentation for the Markup validation contains a lot of
       information on usage, installation, and development. Notably, the
       Help and FAQ document contains a lot of information, and is a
       recommended reading.
     * The Source code availability information page .
     * The development roadmap for this service.
     * How to provide feedback on The W3C Markup Validation Service.

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 & Other Validators

   In addition to this validator, the W3C is offering a number of other
   tools to help you check other types of documents (CSS, RDF, P3P, ...),
   find broken links in your Web pages, and so on. All these tools are
   listed on the W3C's QA Toolbox.

   There are also many excellent tools developed outside W3C to help
   improve the quality of Web pages:
     * HTML tidy, originally developed at W3C, is a program that can help
       automatically clean up HTML pages.
     * Validome offers a very reliable validator for HTML, XHTML and WML,
       in different languages.
     * 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 Quality Assurance
       tools for checking and monitoring your web sites.

   The W3C also hosts a number of other Open Source software projects.

Credits

   The first online HTML validation service was created by Dan Connolly
   and Mark Gaither.

   The W3C Markup Validation Service was created and maintained by Gerald
   Oskoboiny. In a previous incarnation it was known as "The Kinder,
   Gentler, HTML Validator" ("Kinder, Gentler" than Dan and Mark's
   original), but has since found a new home at W3C, and is now maintained
   under the auspices of the Quality Assurance Activity.

   This service uses:
     * Perl and many excellent open source Perl modules (see list in
       installation documentation)
     * A derivative version of James Clark's excellent SGML (and XML)
       parser SP. The version in use for this service is the "OpenSP"
       version from the OpenJade team. For some time it also made use of
       Liam Quinn's modified version, lq-nsgmls.
     * Documentation and Error Explanations originally written by Scott
       Bigham.
     * Interface and Design refinements by Valerio Proietti (and powered
       by Mootools)
     * Patches, Documentation and Ideas from: Aaron Swartz, Björn
       Höhrmann, Brett Bieber, Chris Lilley, Christian Smith, Christoph
       Päper, Dan Connolly, David Dorward, David Tibbe, Etienne Miret,
       Frank Ellermann, Hugo Haas, Henri Sivonen, Ian Hickson, Jim Ley,
       Jukka Korpela Karl Dubost, Liam Quinn, Martin Dürst, Moto Ishizawa,
       Nick Kew, Olivier Thereaux, Patrick H. Lauke, Roland W. Crowl,
       Scott Bigham, Sierk Bornemann, Steph Troeth, Sean B. Palmer, Shane
       McCarron, Terje Bless, Ville Skyttä, ...and the great user
       community on www-validator@w3.org.
