Here, we provide and verify a diffuse layer charging description for both localized electrochemical etching and deposition with ns-voltage pulses. Our primary aim is to quantitatively predict the etching/writing resolution, or spatial extent of a certain applied pulse, based on fundamental constants of the electrolyte and employed experimental parameters. A model based on the time-scale τC, associated with charging of the diffuse layer of the EDL is developed, which provides good quantitative agreement with values reported in literature for electrochemical etching.