Simon Prosser

Debugging tool for theme authors and reviewers.
This tool intercepts all debug information and prints it all out neatly into the footer. It also checks each page for W3C validation. 
This plugin is released as a tool to aid the development of themes and plugins for WordPress and can be used to aid debugging your theme before submission to the themes directory.

Debogger

Debugging tool for theme authors and reviewers.

Barry Kooij

Never5

What The File adds an option to your toolbar showing what file and template parts are used to display the page you’re currently viewing.
You can click the file name to directly edit it through the theme editor, though I don’t recommend this for bigger changes.
What The File supports BuddyPress and Roots Theme based themes.
More information can be found <a href="http://www.barrykooij.com/what-the-file/" rel="nofollow ugc">here</a>.
<h4>Looking for a great related posts plugin for WordPress?</h4>
Another plugin I’ve built, that I’m very proud of is Related Posts for WordPress. Related Posts for WordPress offers you the ability to link related posts to each other with just 1 click! And it’s 100% free! <a href="https://wordpress.org/plugins/related-posts-for-wp/" rel="ugc">Check it out on the WordPress repository.</a>

What The File

This is great plugin to check templates file. It saves a lot of development time with 100% accuracy for me. Thanks to the developers team who worked for this plugin. Every WordPress developer should have this installed during development tier of their website.

Simple, but superb plugin

cool. very helpful !!!!

What The File is the best tool to find out what template parts are used to display the page you're currently viewing!

Debogger vs What The File