This work we illustrate and reflect on the design process of MLTK01, an opensource toolkit for fast prototyping tangible learning things, built on top of Arduino and ml5js. The toolkit was developed as a response to the current lack of fast and easy to use tools for tangible experiments with machine learning. Learning from insights gained through previous projects, we defined a set of basic building blocks necessary to enable such experiments and engaged in an iterative process of sketching, prototyping and preliminary testing of the toolkit. MLTK01 includes a custom PCB, a software library and accessories. Together with a descriptive account of the design process we also discuss possible applications of the toolkit and its implications for a design process of tangible learning things.