will check the compliance against CSS profile specified (CSS3 by default) and report errors and potential problems in Cascading Style Sheets.There are two types of validation events: errors and warnings.In a nutshell: this page lists HTML validators (which check HTML code for standards compliance and errors), CSS validators (which check Cascading Style Sheets for errors and standards compliance), browser compatibility checkers (checks your page to see if it is compatible with various browsers), broken link (or dead links) checkers, accessibility checking (check if your web page is accessible to people with disabilities), etc.Note that this page lists both free online services as well as free offline tools (programs).by Christopher Heng, Whether you design your web page using a visual web editor like Expression Web, Dreamweaver or Blue Griffon, or you code HTML directly with a simple text editor, the generally recommended practice is to validate it after you finish designing it.This article discusses what validation means, points you to some of the free tools that you can use, and deals with its limitations and the problems that a new webmaster may face. Otherwise you'll be completely lost here since I assume you at least know what these terms mean.
You can use the W3 Consortium's HTML validator to check your web documents either by giving it your web page's URL or uploading your document directly to the validator.
The executables may already be downloadable by the time you read this, but if they are not, you can still find older versions at the original HTML Tidy Library Project page with binaries for Windows, Mac OS, Atari, Amiga, Be OS, AIX, Linux, Unix Ware, HP-UX, MSDOS, Solaris, OS/2, Free BSD, RISC OS, Mi NT (Atari) OS, etc. This is an online version of the HTML Tidy validator that you can use to clean up your web pages if you're too lazy to download your own copy.
(To get your own copy, see elsewhere on this page - listed under "HTML Tidy".) The Web Page Purifier allows you to check your HTML pages for compliance ("purity") with various HTML standards (eg HTML 4.0 Transitional, HTML 4.0 Strict, Web TV 1.1, HTML 3.2, etc).
The latest development code for the CSS Validator is available through the Git Hub repository.
For a visual representation, see the CSS Validator Sequence Diagram, which is available in png, graffle and svg formats.