PHP_Debug is an open-source project that gives you useful information about your PHP code that can be used for debugging. It can output processing times of your PHP and SQL, check the performance of particular code blocks and get variable dumps in graphical form, which is great if you need a more visual output than the one given to you by print_r() or var_dump().
DBG is a robust and popular PHP debugger for use in local and remote PHP debugging. It plugs into numerous PHP IDE’s and can easily be used with the command line.
Webgrind is a Xdebug profiling web frontend in PHP5. It implements a subset of the features of kcachegrind and installs in seconds and works on all platforms. For quick N dirty optimizations, it does the job
PHPMD is an easy to configure, user-friendly front-end for the raw metrics that PHP Depend measures. It looks for several potential problems in your code, including possible bugs, suboptimal code, unused parameters, and more.
Xdebug is one of the most popular debugging PHP extensions. It provides a ton of useful data to help you quickly find bugs in your source code. Xdebug plugs right into many of the most popular PHP applications, such as PHPEclipse and phpDesigner.
Gubed PHP Debugger
As the name implies, Gubed PHP Debugger is a PHP debugging tool for hunting down logic errors.
PHP_Dyn is another excellent PHP debugging tool that’s open-source. You can trace execution and get an output of the argument and return values of your functions.
MacGDBp is a live PHP debugger application for the Mac OS. It has all the features you’d expect from a fully featured debugger, such as the ability to step through your code and set breakpoints.
When debugging PHP code, var_dump(), print_r() and debug_backtrace()are usually our best friends. Kint, an open source resource, is a zero-setup replacement that offers a better debugging experience. It smartly detects the type of data being dumped displays tailored alternatives to otherwise hardly readable data. The name of the variable, file, its line and the function wrapping it are all presented.
Whoops is a PHP library for handling errors and debugging them much easier. The library provides stack-based error handling with a good-looking error interface. It has a simple API for dealing with exceptions, trace frames + their data and can integrate with any framework (ready-to-use integrations exist for the end and Silex).
Many PHP developers use print_r() & var_dump() for debugging which output hard to read/unformatted results. Krumo is a replacement for these functions which can display structured information about any PHP variable. Once Krumo is running, the output is displayed in a collapsible DHTML tree built around the structure of the dumped PHP variable. Also, it speeds up the debugging process by the ability to turn it “off” rather than disabling every dumping route inside the code.