8 Essential Website Validators

* This post is regularly updated. *
The Markup Validator is a free service by W3C that helps check the validity of Web documents.

Check Cascading Style Sheets (CSS) and (X)HTML documents with style sheets.

The WDG HTML Validator is similar in many ways to the W3C HTML Validation Service.

This is a validator for syndicated feeds. It works with RSS and Atom feeds.

This tool allows you to check how web 2.0 your site is.

Validome offers a very reliable validator for HTML, XHTML and WML, in different languages.

Site Valet is a comprehensive set of Quality Assurance tools for checking and monitoring your web sites.

XML validation form offers full XML 1.0 validation facilities.