xdebug

Xdebug is a debugging and productivity extension for PHP

Xdebug and provides a range of features to improve the PHP development
experience.

Step Debugging
A way to step through your code in your IDE or editor while the script is
executing.

Improvements to PHP's error reporting
An improved var_dump() function, stack traces for Notices, Warnings, Errors
and Exceptions to highlight the code path to the error

Tracing
Writes every function call, with arguments and invocation location to disk.
Optionally also includes every variable assignment and return value for
each function.

Profiling
Allows you, with the help of visualisation tools, to analyse the
performance of your PHP application and find bottlenecks.

Code Coverage Analysis
To show which parts of your code base are executed when running unit tests
with PHP Unit.

License: Xdebug-1.03