Allan Collins

Is your website up to W3C HTML coding standards? This plugin will allow you to test each page or post on your site against the W3C Validator.
Want to contribute? Fork it: https://github.com/allan23/validated

Validated

This plugin will allow you to check your pages/posts HTML against the W3C Validator.

Joan Botella

A plugin with common features missed in WordPress, like favicon, meta tags, adding HTML to head and footer, WordPress e-mail from header filter, etc.
I’ve developed this plugin for my own job. I’ve realized that when I create a 
new WordPress project, there are some features I have to plugin every time. I 
decided to bundle they all into a single plugin, and I’m publishing it for 
other creators who may find it useful too.
Take a look to the <a href="https://wordpress.org/extend/plugins/jb-common/changelog/" title="Go to the Changelog section" rel="ugc">Changelog</a> 
for a complete feature list, you may be interested in some of them.

JB Common

A plugin with common features missed in WordPress, like favicon, meta tags, adding HTML to head and footer, WordPress e-mail from header filter, etc.

Validated vs JB Common