Abstract A shorthand notation for encoding most of the known electrochemical mechanisms is proposed. A few symbols allow different kinds of charge transfer (heterogeneous, homogeneous) and all kinds of chemical reactions such as reactant addition or elimination, intramolecular reactions, cleavages, dimerization or coupling to be taken into account. Also, H-atom transfers and photochemical steps like excitation, deactivation or energy transfer are very simply notated. Branching or parallel pathways and any degree of intricacy are possible in a one-line notation without any graphical sign. Easy typing on any typewriter or computer keyboard is one of the main advantages of this notation. Provision is made for the notation of overall reactions and also for cases of uncertainties in step ordering. A large set of referenced examples is provided as an encoding guide. Adsorption-desorption steps are not treated here and will appear in Part II, together with notation of solvated electron transfers, deposition, dissolution, surface reactions, interphase exchange and other complications.