First-principles simulations have been employed to simulate the inelastic electron tunneling (JET) spectra of the enol and keto forms of an anil molecular switch and to analyze them with respect to the character of the vibrational normal modes. When the molecules are sandwiched between Au plates, the dominant JET signatures appear at very similar voltages for both forms, but their intensities are clearly different, which makes JET an efficient technique to probe the molecular state of the switch. The JET-active modes are also similar for both anil forms and consist of in-plane molecular motions, CC and ring stretching, and C-H bending motions. Moreover, the JET activity of the vibrational modes specific to the enol and keto forms, i.e., those involving bending motions of the C-O-H and C-N-H groups, respectively, demonstrates that JET spectroscopy is an efficient technique to distinguish unambiguously between the two states of the keto/enol switch.