The Query Monitor plugin was released by John Blackbourn in late November of 2013 and became an instant hit with WordPress developers. It’s racked up 25 five-star reviews on WordPress.org and today crossed the 10,000 download mark, which doesn’t even factor in the number of times the Github repo has been cloned.
Query Monitor is without a doubt the most comprehensive debugging plugin for WordPress, often replacing multiple plugins developers previously combined to try to get the same tools. Its features are too long to list, but suffice it to say that it offers a solid overview of database queries, hooks that are being fired, theme template information, HTTP Requests, Redirects and much more.
If you use it on a community site, there’s a separate extension that will add bbPress and BuddyPress conditionals to Query Monitor’s output.
The plugin is updated quite often and the most recent 2.6.6 release adds more robust support for alternative database drivers (including mysqli in core). Nearly every topic in the plugin’s support queue is marked as resolved and John Blackbourn is very responsive to issues and questions on Github. It’s easy to see why Query Monitor has so quickly become a must-have debugging plugin for WordPress developers.
If you haven’t yet tried it, you can download Query Monitor from WordPress.org. Site admins and multisite super admins will have access to its output in the admin bar.