Ivan Guardado has posted a recent tutorial looking at debugging your PHP code with the help of a popular tool - FirePHP (that interfaces with an equally popular Firefox extension, Firebug).

Nowadays, the code debugger is a tool that has almost all programing environments which allows you to watch the internal work of your applications and finding errors at run time for a easy way. The trouble is when you are working in a client-server architecture model, because from where you send the request (client) can not access the code hosted on the server.

He points out FirePHP as one that doesn't require this sort of installation. Included is a quick tutorial on getting it up and running for your development environment as well as the output formats and how to handle the output you want for debugging only.