In this work, Extended-connectivity Fingerprint (ECFP) (Rogers and Hahn, 2010) is adopted as the molecular descriptor. Thus, ECFP is implemented natively in our e-Bitter program due to the following three factors. (1) ECFP, one typical class of topological fingerprints, was manifested to be powerful in the classification (Ekins et al., 2010; Rogers and Hahn, 2010; Chen et al., 2011; Hu et al., 2012; Braga et al., 2015, 2017; Koutsoukas et al., 2016; Rodríguez-Pérez et al., 2017; Varsou et al., 2017; Wang et al., 2017; Yang et al., 2017). However, ECFP has not been applied to the general classification of diverse bitter/bitterless compounds in the literature. (2) The existing softwares with the ECFP function such as Pipeline Pilot (http://accelrys.com), JCHEM (https://www.chemaxon.com), and RDKit (http://www.rdkit.org) etc. cannot provide a facile and intuitive mean to highlight the fingerprint bit “1” in the context of the 3D structure and also cannot inform us the importance of each bit. But it is worth mentioning that Bioalerts program (Cortes-Ciriano, 2016), which is developed based on the RDKit, can offer a very useful function to generate the 2D structure image highlighting with one ECFP bit. Nevertheless, Bioalerts doesn't have a 3D graphic frontend to support the interactive visualization. (3) The native integration of ECFP in our e-Bitter program will decrease the software dependency on any other packages and will be convenient for the users to deploy this program on their own computers. The implementation of ECFP is given as follows.