Nikoya

Check the doctype validity using W3c validator (html , xhtml , … ) when creating or updating page / post / custom post type and show the result in backend 
It show the result in back-end in sortable column, a link is add to the w3c for all file to help you to correct html error.
Very easy to see if a post / page is valid or not.
This plugin can check the W3C validity of your page / post or custom post type even if the site is not accessible from the Internet (if you work on local system for example)

(x)html easy validator

Check the doctype validity using W3c validator (html , xhtml , ... ) when creating or updating  page / post / custom post type and show the result in  …

tammax

Automatically checks the validity of the page with the service provided by the site http://validator.w3.org/
Verifica in automatico la validit? della pagina grazie al servizio fornito dal sito http://validator.w3.org/

W3C validation auto check

Automatically checks the validity of the page with the service provided by the site http://validator.w3.org/

(x)html easy validator vs W3C validation auto check