The main aim of this paper is to evaluate a new software application to support experts involved in decision-making in the ?eld of sustainable energy planning in isolated regions. The prototype named Energy Fuzzy-On is designed for this purpose. It implements various fuzzy concepts (fuzzy rules, fuzzi?ed input data, fuzzy variables utilized by fuzzy terms and related fuzzy sets) chosen to obtain reasoning in case of unclear, uncertain, or even incomplete input data for reaching a conclusion about them. These data are input for a linear fuzzy multi-objective decision model developed in GAMS, where two objectives, environmental and economic objectives are minimized to obtain a set of non-dominated solutions. These solutions are used as input for a fuzzy multi-attribute model developed in the fuzzy toolbox of MATLAB. The environmental and economic criteria together with the social and technical criteria are used as inputs for choosing the most sustainable alternative. Finally, the tool is assessed in Medio Atrato-Chocó, a small, isolated village of West Colombia, where currently the energy service is supplied by small diesel generator sets. The selected and most sustainable solution, for a planning horizon of ten years, is composed of a hybrid system (54 % diesel generators, 39.3 % small hydro and the rest with gasification of biomass, from agricultural waste).