W3C validation

The W3C validation is not actually necessary for good SEO, however keeping the code that your site has been built by is very relevant. W3C validation is a standard tool that many website designers and developers use that tells them if there are any errors in the code. It is advisable to use a designer that has a W3C validation button on their site as it confirms their abilities (clicking on this button tells you if there are any mistakes to their site).