When working to debug WordPress projects, I’m personally a fan of using Codebug (something I should probably write about a bit later), but it’s more of a general debugger than one specifically tailored for WordPress.
If you’re looking for the later, then there’s a solid plugin available from Tonya Mork (of Know The Code) that brings the features of Kint Debugger into a WordPress plugin.
For those who have never used a professional-grade debugger, this is a great way to get started with going beyond the standard print_r and var_dump statements that so many often use to locate problems.

