When writing HTML code and building web pages, a HTML validator can be used to check and make sure the HTML code is correct, valid, and follows W3C standards set for HTML scripting. The HTML validator can check all the HTML markup and point any invalid code or any code that should be updated to better meet the W3C standards. Some HTML validators can also check XHTML, MathML, and SMIL scripting for validity.
Many free HTML validators available. Some of them are web-based, meaning the HTML file can be loaded into the online validator and checked without having to install anything on the computer. Other validators work by being installed in the web browser as an extension or plug-in, or installed on the computer as a software program.
The W3C Markup Validation Service is one of the best HTML validators available, as it remains up-to-date with all new and updated HTML standards. The W3C validator allows a user to check HTML code by providing the URL of the web page, by uploading the HTML file, or by copying and pasting the HTML code into the validator.