The W3C Markup Validation Service
Rated • 104 reviews • web design, web, xhml, html, markup validation service • w3.org
The W3C Markup Validation Service
The first step towards achieving proper web-design.
This is the W3C Markup Validation Service, a free service that checks Web documents in formats like HTML and XHTML for conformance to W3C Recommendations and other standards.
if you wish to validate specific content such as RSS/Atom feeds or CSS stylesheets or to find broken links, there are other validators and tools available.
Why is validating important, or even relevant? Because poorly-written markup is completely unpredictable; you end up relying on a browser's error-handling, and even though most browsers are very good about this, it's a bad practice to rely on it. The single point is, validating helps you spot errors in your code, which in turn ensures more consistent rendering of your page.

