Senff - a11n

<h4>Summary</h4>
Simple Debug Info Panel for WordPress will enable you to instantly see some “under-the-hood” debugging info for your site. With one click (or none at all), you can see which template is being used, what the post/page ID is, the current screen/viewport size, any categories a post is assigned to, and some more.
Every item’s visibility can be turned on or off, so you have complete control over what will be shown in the infobox.
<h4>Features</h4>
<ul>
<li>Shows template information: see which template is being used for any page you’re looking at.</li>
<li>Shows post/page ID: gives you the internal WordPress ID of the current post/page.</li>
<li>Categories/tags: shows relevant categories and tags of the post/page (if they are not displayed on the page itself).</li>
<li>Screensize indicator: shows the viewport size, updates in real time (so you can figure out why styles within a certain media query are applied or not).</li>
<li>Turn on/off which information you want to see: you can choose whatever you want the infobox to show. </li>
<li>Positioning of box: choose placement of the box from 4 options (top left, top right, bottom left, bottom right)</li>
<li>Default shows or hides: choose whether infobox should be open or closed/minimized by default</li>
<li>Admin Only-mode: make infobox only visible on the front end to users logged in with admin rights.</li>
</ul>

Simple Debug Info Panel

Simple Debug Info Panel shows a little box on your site with helpful debugging info for developers: post/page ID, which template is being used, etc.

Jick

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Simple Debug Info Panel vs Hab.la for WordPress