Check the markup (HTML, XHTML, …) of Web documents
Documentation for the W3C Markup Validator
Here you will find the documentation for The W3C Markup Validation Service.
We are constantly working on improving this documents and adding
new elements, and eagerly welcome feedback and additions!
Table of contents
●For beginners and experts alike
●Experts only
For beginners and experts alike
W3C Markup Validator
Help and FAQ
A quick intro and help to get you started, with answers to
Frequently Asked Questions. Read this first.
This document has a lot of information on how the validator works, answers to frequent
questions about "why did the validator say that...", as well as pointers to technical
and policy documents.
W3C Markup Validator User's Guide
The User's Guide and tips for the W3C Markup Validator. It notably lists
and explains the available options.
W3C Markup Validator Error Messages
Explanations of common error messages.
This list conveniently gathers
all the error messages currently used by the validator when processing Web documents,
and the community-contributed explanations to these error messages, whenever available.
Favelets
Favelets, a.k.a Bookmarklets: Validation made fast and easy
Access Keys
Quick navigation with the access keys used throughout this site.
Experts only
Development Roadmap
high-level overview of past and future releases.
Download / Source
Information on source code availability and download instructions for the Markup Validator.
Installation Guide
Step-by step guide for the installation of the Markup Validator
on your server.
Markup Validator Web Service API
Use the validator from your applications with the experimental Markup Validator Web service, and its open API.
Developer Information
Information for programmers wanting to play with the validator's code, and/or contribute to its development.
SGML, Validation and the Markup Validator
An introduction to concepts of SGML, DTDs and formal validation, and how they apply to the
Validator, with links to further information.
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Markup Validation Service