Mario Peshev

Theme Mentor is a cousin of the Theme-Check plugin getting deeper into the code analysis.
It’s using different approaches to monitor for common problems regarding theme reviews from the WordPress Theme Reviewers Team. It is prone to fault analysis, so use only as a reference for improving your code base even further.
Currently supported validations:
<ul>
<li>Mark all tags in template files</li>
<li>Mark all tags in template files</li>
<li>Warn about query_posts() usage</li>
<li>capital_P_dangit control (disallow any WordPress spelling other than WordPress as is – that is WORDPRESS and WordPress, ugh)</li>
<li>wp_deregister_script(‘jquery’) is forbidden</li>
<li>wp_dequeue_script(‘jquery’) is forbidden</li>
<li>prevent global $data; call as a common troublemaker (props @pippinsplugins)</li>
</ul>
header.php specific
<ul>
<li>Make sure that wp_head is before </li>
<li>Ensure that wp_title(…) is called within and tags</li>
</ul>
footer.php specific
<ul>
<li>Make sure that wp_footer is before </li>
</ul>

Theme Mentor

Theme Mentor is a cousin of the Theme-Check plugin getting deeper into the code analysis.

DareBoost

Performance Tester is a WordPress plugin that allows you to launch a performance and quality analysis on your WordPress home page directly from your backoffice. 
The report is provided by <a href="https://www.dareboost.com" rel="nofollow ugc">DareBoost</a>.
Easily launch an analysis and get :
<ul>
<li>Major metrics of web performance (loading time, page weight) and DareBoost score</li>
<li>Relevant performance timings (first byte, page interactive, page fully load)</li>
<li>3 improvement priorities to optimize your WordPress</li>
<li>A direct access to a full report on <a href="https://www.dareboost.com" rel="nofollow ugc">DareBoost</a>, with all your issues and recommandations to optimize your website (for free)</li>
</ul>

Performance Tester

Analyze the home page of your WordPress site directly from your backoffice and get a quality and performance report.

Theme Mentor vs Performance Tester