PHP Debug is a single file API for tracing PHP applications.
You can add, with minimal impact, diagnostics to be displayed upon program termination. Each diagnostic contains file, function and caller function information as well.
Just an API, not a class. Just include the debug.php file and add
debug() calls throughout your code similar to
var_dump(). However, the diagnostic messages are stored and displayed as a list at program termination. The diagnostics can be disabled and controlled in other ways.
It's small and simple yet very versatile and includes demonstration/testing code.
PHP debug on Github. PHP debug at SourceForge. There is a Go debug, and a Perl debug.