In this paper, a serial port based debugging tool for the Arduino platform is presented. The tool is based on a modification of the Arduino IDE (Integrated Development Environment) and libraries. It includes the basic options of debugging tools (stepping, breakpoints, variable inspection, etc.) without the need of a hardware debugging interface. The tool has been designed taking into account that is going to be used by beginners or intermediate users, which is the most common profile among Arduino users. The tool tries to promote debugging procedures that are not based on trial and error, and contributes to the Arduino environment with another teaching resource.