Petri nets are a powerful formalism for modeling and analyzing concurrent, distributed, and complex systems. However, extensions that enable greater representative capabilities (e.g., coloured Petri nets) include significant complexities beyond elementary Petri nets or even Turing complete Petri nets with inhibitor arcs. Currently, there is a lack of free and open-source Petri net tools that are both maintained and free of the complications of coloured Petri nets. In this paper we present a free and open-source Petri net editor and simulator, MyPetri.net, that provides a modern web-based editor for Petri nets and several modes of execution or simulation. While more complex editors offer formal verification methods, our approach introduces a unit testing–like framework that allows users to set and verify place values after execution, similar to traditional software testing. Finally, we present an informal discussion on the impact of the MyPetri.net tool in the classroom.