www.validator.w3.org is a Markup validation service which helps check the validity of Web documents.

Most of the web documents are writtern in HTML or XHTML , these languages are machine-readable. The act of checking a document in called Validation. This markup validator helps to check the machine readable vocablury.

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.

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 Tool box.

Visit : w3.org for more about www consortium.�