Roland Rust

It functions as a frontend for the Markup Validator Web Service API on http://validator.w3.org. Stylesheets are checked as well.
Languages available: 
+ english 
+ deutsch(german)

Batch Validator

This plugin performs a batch markup validation check over your entire WordPress website.

seshelby

The HTML Validation Plugin runs in the background, identifies and reports HTML validation errors on your website. Once activated, the HTML Validation plugin uses WordPress cron to scan your website content in the background. A progress bar on the report screen indicates scan progress. HTML Validation is provided by <a href="https://about.validator.nu/" rel="nofollow ugc">Validator.nu</a>. Please refer to the provided <a href="https://about.validator.nu/#tos" rel="nofollow ugc">privacy policy and terms of use</a>. Posts may also be scanned using the Validate HTML link provided on the “All Posts” screen.
The HTML Validation Pro extension adds options to automatically correct many HTML Validation issues. This one of a kind plugin could save you hundreds of hours of work finding and correcting HTML validation issues. <a href="https://www.alumnionlineservices.com/php-scripts/html-validation/#proext" rel="nofollow ugc">Visit our website to learn more and add the Pro Extension</a>

HTML Validation

The HTML Validation Plugin runs in the background, identifies and reports HTML validation errors on your website. Once activated, the HTML Validation  …

Batch Validator vs HTML Validation