Recently, the demand for designing mechanism-embedded artifacts has increased in personal digital fabrication. However, it is difficult for nonexperts without engineering knowledge to design and build a prototype with a kinetic mechanism. We present M.Sketch, a prototyping tool that helps nonexperts to design and build linkage-based kinetic mechanisms. It enables the user to easily configure the linkage-based mechanism with a simple interface applying a geometry drawing metaphor. The tool features computational support, including interactive visualization, top-down optimization, and connection to digital fabrication, to obtain and build the desired movement. In order to support science–art integrated science, technology, engineering, the arts, and mathematics (STEAM) education related to digital fabrication of interactive artifacts, we deployed M.Sketch in design workshops and student contests of walking robot design. The participants in the contests were able to successfully design and build walking robots with the Theo-Jansen mechanism using various support features of M.Sketch. Based on the development and deployment in science, technology, engineering, the arts, and mathematics educational domains, we figured out several implications, and further improvement points of prototyping tools supporting nonexperts in designing mechanism-embedded interactive artifacts.