Every stochastic Petri net is a chemical reaction network in disguise: molecules change count one firing at a time, and under modest assumptions that process is exactly a Continuous-Time Markov Chain (CTMC). Gillespie’s stochastic simulation algorithm (SSA) draws a true trajectory of that chain — no time step is guessed; each firing happens at the freshly simulated time of a correctly weighted exponential clock.

Below, pick a well-known network, tune the kinetic rate constants, add trajectories. Each line is exact, which matters: it’s the ground truth that model checkers and approximation schemes must match.