shawfactor

This plugin logs all wordpress queries in the current page request as a html comment at the end of your output.
It only does so when the get variable lh_log_queries is set. That variable has three settings. 
1. queries: this logs queries only 
2. hooks: this logs hooks only 
3. both: this logs both hooks and filters
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LH Log Queries and hooks

Decisions not options for query and hook logging

Eugen Bobrowski

This is tool that help developers and administrators easier getting information.
The debug bar is available on front side for everyone if WP_DEBUG is true. If you are admin you can open bar on any page. Hover the mouse cursor to bottom right corner and click on
<h4>Features:</h4>
<ul>
<li>Implementation time counter</li>
<li>Queries counter</li>
<li>Queries list (sortable)</li>
<li>Memory counter</li>
<li>Segment checker</li>
<li>Cron jobs information</li>
<li>WP_Cache counter</li>
<li>phpinfo() window</li>
<li>References menu</li>
<li>Image Puller that provide pull missed images from production to develop site</li>
</ul>
Implementation time counter
It count the time from plugin loaded action to debug bar. 
It does not consider processes that implement before and during the plugins are loading.
Queries counter
It count all what is queried via $wpdb object.
Queries list
It show all what is queried via $wpdb object.
The <code>SAVEQUERIES</code> constant must be defined as <code>true</code>.
Memory counter
Returns the amount of memory, in bytes, that’s currently being allocated to your PHP script.
Segment checker
Also you can check any segment of your code.
<pre><code>do_action('check_segment', 'segment_1');

//do somethisng

do_action('check_segment', 'segment_1');
</code></pre>
The code below returns in debug bar new item like this:
<blockquote>
segment_1: 14.14/3/1
</blockquote>
The digits there ara time, queries and how many times this code was implemented.
References menu
The default one item of this menu is Errors. It shows notices and warnings including case when <code>WP_DEBUG</code> is false.
And also you can easy add your item to this menu and print there any var_dump or anything else.
<pre><code>add_filter('wp_debug_refs', 'my_debug_tool_ref');

function my_debug_tool_ref ($refs) {

 global $post;

 $refs['my_ref_id'] = array(
 'title' => 'My ref',
 'content' => 'My ref' . var_export($post, true),
 );
 return $refs;
}
</code></pre>

Debug Tool

Show helpful debug bar at front and admin side. Tool for developers.

LH Log Queries and hooks vs Debug Tool