Vertical slot fishways are widely used and are generally very effective in ensuring fish passage. The appropriate design of a vertical slot fishway depends on an interplay between hydraulic and biological variables, since the hydrodynamic properties of the fishway must meet the requirements of the fish species for which it is intended.This paper presents a tool designed to analyze the efficiency of a fishway model according to biological criteria. The application can be used either in the analysis of an existing fishway or in the design process of a new one. It allows the user to choose between a wide range of geometric dimensions of the pools and the slot, and between different fish species. If it is being used as a design tool, it provides feasible fishway models sorted according to their biological efficiency.Considering the complexity of the hydraulic and biological phenomena involved in the process of swimming through a fishway, the tool presented here does not intend to determine an optimum design, but rather to establish an objective way for comparing different fishway designs, considering not only hydraulic aspects but also trying to quantify biological aspects of the target fish species.