W3C Markup Validation Service

The Markup Validation Service is a validator by the World Wide Web Consortium ( W3C), can check for well-formed markup can help internet users in the document description languages ​​HTML and XHTML. Markup validation is an important step to ensure the technical quality of Internet pages; However, it is not a complete measure for compliance with web standards.


The Markup Validation Service began as a project of Gerald Oskoboiny under the name The Children, Gentler HTML Validator. It was developed as a more intuitive version of the first online HTML validator, which by Dan Connolly and Mark Gaither wrote and was announced on 13 July 1994.

In September 1997 Oskoboiny began to work for the W3C and on 18 December 1997, the W3C announced the W3C HTML Validator, which was based on his work.

W3C also provides validation tools for various web technologies in addition to HTML / XHTML to, for example, CSS, XML schema and MathML.

Supply the browser

Many major browsers are often tolerant of different error types, and make a document mostly error-free device, even if it is not syntactically correct. Various other XML documents can be validated with the Markup Validation Service, provided they hold a reference to an internal or external DTD.

Criticism of the Validator

All markup validators suffer from the inability to see the "whole picture " of a website. However, such shows often do when it comes to finding missing closing tags and other formalities. This does not mean that the page is displayed in all browsers within the meaning of the creator.

DTD based validators also have limited ability to evaluate attribute values ​​as defined in the specification documents. For example, using the document type HTML 4.01 DOCTYPE, bgcolor = " fffff " as valid for the "body" element accepts, even though the value " fffff " prepending a ' #' character is missing and it is only 5 ( instead of 6 ) hexadecimal contains. Moreover element is width = "really wide" considered valid also for the " img ". DTD based validators are technically not able to test for these types of attribute value problems out.

In addition, sites should be tested in as many browsers as possible, to ensure that the limitations of the Validator to be compensated and the website to operate correctly.

CSS validation

While the HTML / XHTML W3C Validator evaluates only pages that are written in such formats is another validator, such as the W3C CSS Validator requires that there are no errors in the associated cascading style sheet to make sure. CSS Validator function in a similar way as HTML and XHTML validators, they turn current CSS standards referenced in CSS documents.