Selectivity calculator for overcurrent protection devices. This is a tool that allows you to calculate the selective operation of circuit breakers taking into account the actual currents flowing in the circuit breakers, taking into account short-circuit currents, also additionally, the calculator allows you to build the starting characteristic of an electric motor. Calculation results are presented in a graphical form convenient for interpreting results. The calculator's algorithms are based on general provisions on the selective operation of protection devices in low-voltage circuits. The calculator implements an assessment of the selective operation of selected protection devices. At the moment, the assessment of the selective operation of circuit breakers is implemented only for current selectivity.