GFA - tool is an open-source QGIS plug-in to realize a fast and cost-effective delineation of the floodplains in the contexts where the available data is scarce to carry out hydrological/hydraulic analyses. This algorithm uses the linear binary classification technique based on the recently proposed Geomorphic Flood Index (GFI), (Manfreda et al., 2015; Samela et al., 2016; Samela et al., 2017)