Surge for the advancement of sensor that accurately and selectively detect toxic materials particularly cyanides and fluorides, is expanding every day. Herein, we analyze the sensing ability of carbon nitride (C6N8) monolayer for precise detection of hydrogen cyanide (HCN) and hydrogen fluoride (HF) using DFT approach. Interaction energy analysis reveals that HF binds strongly to C6N8 monolayer which is probably due to chemical bond formation whereas, HCN adsorbed to the surface by weak van der Waals forces. The atom in molecules (AIM), the density of states (DOS), non-covalent interaction (NCI), molecular electrostatic potential (MEP), electron localization function (ELF), frontier molecular orbitals (FMO), and QNBO were used to gain a thorough understanding of the complexation of HCN and HF with monolayer. HCN and HF analytes with C6N8 monolayer exhibit slight variations in band gap energy in FMO analysis (4.206 to 4.267 eV) indicating weak NCIs. Furthermore, MEP map demonstrate that more charge transfer is occurred from the C6N8 monolayer towards HF@C6N8 resulting in a strong ionic bonding. In addition, the existence of non-covalent interactions among complexes confirmed by NCI-RDG and QTAIM analysis. A short recovery period for HCN@C6N8 (1.677 × 10−7 s) makes desorption process simpler. Appreciable selectivity of monolayer towards analytes and prospects of all findings will provide an experimentalist with practical suggestions to build highly sensitive sensors for HCN and HF using C6N8 monolayer.