Timed Event Graphs (TEGs) constitue an important class of Discrete Event Systems that have a wide domain of applicability. Analysing the temporal behavior of these systems has proven to be efficient, primarily through the use of max-plus algebra and more particularly with formal series of MinMax[[gamma,delta]] semiring. We present, MinMaxGDJS, a web toolbox to handle formal series in MinMax[[gamma,delta]] semiring. Making the library accessible on the web makes it easier to experiment and calculus with formal series without the overhead of configuring and building the C++ library. Web browsers become an excellent platform for giving portable demos.