A new naphthaldehyde based probe 1-((benzylimino)methyl)napthalen-2-ol (NB) synthesized in a single step was designed and characterized by various spectroscopic techniques (NMR, IR, HRMS) and FESEM. The colorimetric and optical sensing properties of the designed probe towards various metal ions were investigated through UV–vis absorption spectroscopy. The synthesized probe showed dual sensing behavior in methanolic solution for Hg2+/Cr3+ ions via colorimetric and spectral changes. Detection limit of the probe for Hg2+/Cr3+ ions was calculated as 2.7 × 10−8 M and 1.1 × 10−8 M respectively. Detection of these ions by the bidentate probe in 1:1 ratio is due to the presence of hydroxyl group and imine group. The synthesized probe works well in pH range 3 to 10. Theoretical calculations also supported the binding mechanism. The synthesized probe was also successfully implemented in different spiked water samples to calculate the percentage recovery. In order to check the practical efficiency, paper strip test was performed for Hg2+/Cr3+ ions detection.