Xdebug

Xdebug is a PHP extension that adds debugging, diagnostics, and analysis features to the language. It addresses common development tasks such as stepping through code while a script runs, getting clearer error output with stack traces for notices, warnings, errors, and exceptions, and inspecting execution paths when something goes wrong.

Its main capabilities include step debugging from an IDE or editor, an improved var_dump(), function-call tracing written to disk with optional variable assignments and return values, profiling output for use with visualization tools to locate performance bottlenecks, and code coverage analysis showing which parts of a code base run during PHPUnit unit tests. Xdebug Cloud is offered separately as a Proxy-as-a-Service for networking situations such as developers working remotely against a shared development server on a private network.

Xdebug is aimed at PHP developers working in an IDE or editor and at teams running PHPUnit tests. The extension is distributed in numbered releases, with alpha versions published alongside stable ones.