Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
W3C Markup Validation Service
open-in-new
<p>The Markup Validation Service is a <a href="/facts/Validator/WUBnT6QT">validator</a> by the World Wide Web Consortium (W3C) that allows <a href="/facts/Internet/Xw1rVvJU">Internet</a> users to check pre-HTML5 <a href="/facts/HTML/sSc3fT78">HTML</a> and <a href="/facts/XHTML/6qHnmJSg">XHTML</a> documents for <a href="/facts/Well-formed_element/7Xrmp0fA">well-formed</a> markup against a <a href="/facts/Document_type_definition/JsvY9PyQ">document type definition</a> (DTD). Markup validation is an important step towards ensuring the technical quality of web pages. However, it is not a complete measure of web standards conformance. Though W3C validation is important for browser compatibility and site usability, it has not been confirmed what effect it has on <a href="/facts/Search_engine_optimization/RNzIbb62">search engine optimization</a>. </p><p>As <a href="/facts/HTML5/HBAxEAr6">HTML5</a> has removed the use of DTD in favor of a "Living Standard", the traditional Markup Validation Service is not applicable to these formats. Validation is instead performed using an open-source "Nu Validator", an instance of which is provided by W3C. </p>