The development of efficient electrocatalysts for fundamental research and research-and-development requires identifying, understanding and ultimately tuning key experimental parameters. This goal is achieved by performing systematic studies where only one of the multiple parameters influencing the catalytic properties is studied at a time, independently of the others. Even though a systematic investigation of catalyst properties can be tedious and time consuming, it provides deep and significant insights into catalyst design to improve catalytic activity, selectivity and/or stability. A toolbox concept developed along the years based on surfactant-free colloidal syntheses is here detailed. It is stressed how this toolbox approach leads to a better understanding of catalyst properties with the examples of platinum nanoparticles for the oxygen reduction reaction (ORR) and iridium nanoparticles for the oxygen evolution reaction (OER).