Trace the execution time of plugins, themes and core files to find the bottlenecks of your system.

F12-Profiler

This plugin will track the load time of each plugin, javascript and css file 
to help you optimizing the performance of your WordPress site. It will help you 
to figure out which plugin / resource causing the slowness of your page.
Track time for:
<ol>
<li>Core</li>
<li>Theme </li>
<li>Plugins</li>
<li>Resources (JavaScript, CSS)</li>
<li>External files</li>
</ol>

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