The W3C Markup Validation Service
Or are you thinking about using a new web design company and wondering how clean their code is?
Fortunately there is a very easy way to check virtually any website for coding errors. The W3C Markup Validation Service is the industry standard for checking coding errors. And it’s free: Test Here in W3 Validator
Just enter the home page URL of any website you want to check. You can also test inner page URLs.
A cleanly coded site is more likely to offer a better customer experience. And it could even make the difference in how your website is ranked by the search engines.