Xdebug is an extension for PHP, 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.