For a visual guide on building custom features from scratch using script-based tools, you can watch this demonstration: Creating a Custom Feature with FeatureScript Onshape• Jun 15, 2017
If this is part of an automation workflow (formerly Integromat): ANUJSINGH_COLLECTION_145DSSIzip
: You can create custom parametric features using FeatureScript . This involves building a basic feature code structure and using queries to define successful parametric operations. For a visual guide on building custom features