PHP Debug is single API for tracing PHP applications. With a single file of only 200 lines, you can add, with minimal impact, diagnostics to be displayed upon program termination. Each diagnostic contains file, function, and caller function information. You just need to include the debug.php file and add debug() calls throughout your code in the same way as var_dump(). The diagnostic messages are stored and displayed in a list. Diagnostics can be disabled and controlled. It's small and simple yet very versatile.