The synthesis, characterization, and evaluation of inhibiting performance of two xanthene derivatives, namely 3-oxo-3H-spiro[isobenzofuran-1,9′-xanthene]-3′,6′-diyl (3-dibenzoate) (NAR2) and 3-oxo-3H-spiro[isobenzofuran-1,9′-xanthene]-3′,6′-diyl (3-diacetate) (NAR3) on mild steel immersed in 1 M HCl solution are performed. The in vivo tests were carried out to confirm the non-toxicity of NAR2 and NAR3. The solutions corrosive was analyzed using UV visible Spectroscopy. The recorded spectra confirm the adsorption capacity of these molecules on the surface of iron and thereby a formation of Fe–inhibitor complex film. A combination of Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX) Spectroscopy were performed to characterize the surface of mild steel, with and without the NAR2 or NAR3 inhibitors; and Electrochemical techniques were evaluated (EIS) to determine the corresponding corrosion inhibition efficiencies of NAR2 and NAR3. The Density Functional Theory (DFT)- based total energy calculations and Monte Carlo simulations were also performed to get further theoretical insights into the inhibition mechanism. The obtained results confirmed that both organic inhibitors exhibit non-toxicity, with an inhibition efficiency of 93% and 89% for NAR2 and NAR3 at 10−4 M concentrations, respectively. Also, the both inhibitor function as mixed (cathodic and anodic) type inhibitors, displace water molecules from mild steel, and form an heterogeneous films on the mild steel surface to protect against corrosion.