Onshape custom features are specialized modeling tools written in FeatureScript that live directly within the Part Studio toolbar and feature list, behaving exactly like native commands (such as Extrude or Fillet) to parametrically generate or modify geometry. In contrast, Onshape custom apps are external applications connected via the API that extend the platform’s ecosystem with broader capabilities—such as rendering, simulation, or CAM—typically operating in a separate tab or an integrated panel rather than functioning as a sequential step in the model’s design history.