In the teaching of graph theory algorithms it is important that students can experiment them on numerical instances in order to fully understand their logical meaning and to learn how they can be implemented. We developed an open source Java framework to help students in their approach to the study of graph algorithms. The framework was implemented so as to be portable and easy to use. In addition, we included a library that anyone can easily use to develop custom algorithms. The framework, which is currently in use at the University of Bologna, and is available on-line includes an intuitive graphical user interface, and gives the users the possibility of performing a "step-by-step" execution.