GTmetrix

GTmetrix has created GTmetrix for WordPress – a WordPress plugin that actively keeps track of your WP install and sends you alerts if your site falls below certain criteria.
Run analyses, schedule reports on a daily, weekly or monthly basis, and receive alerts about the status of your site all from within your WordPress Admin!

GTmetrix for WordPress

Plugin isn't showing the toolbar link in the latest version of WP now :(

Fantastic plugin but...

GTmetrix can help you develop a faster, more efficient, and all-around improved website experience for your users. Your users will love you for it.

Berrie Pelser

Widget to test website performance by <a href="http://www.gtmetrix.com" title="gtmetrix.com" rel="nofollow ugc">GTmetrix.com</a>
* Coding by <a href="http://www.mijnpress.nl" title="MijnPress.nl WordPress development" rel="nofollow ugc">MijnPress.nl</a> 
* Idea by <a href="http://hosting.ber-art.nl" title="Hosting.Ber-art.nl WordPress Webhosting" rel="nofollow ugc">hosting.ber-art.nl</a>

GTmetrix website performance widget

Widget to test website performance by GTmetrix.com

GTmetrix for WordPress vs GTmetrix website performance widget