Clockwork - php dev tools in your browser - server-side component
Xdebug — Step Debugger and Debugging Aid for PHP
Laravel Debugbar (Integrates PHP Debug Bar)
PHP errors for cool kids
The Debug component provides tools to ease debugging PHP code.
The VarDumper component provides mechanisms for walking through any arbitrary PHP variable. It provides a better dump() function that you can use instead of var_dump().
Tracy: the addictive tool to ease debugging PHP code for cool developers. Friendly design, logging, profiler, advanced features like debugging AJAX calls or CLI support. You will love it.