YANG data models and how NETCONF and RESTCONF use them

YANG (Yet Another Next Generation, RFC 7950) is a data modeling language. A YANG model does not hold configuration itself; it defines the structure, names, data types and constraints of configuration and operational data, like a schema. Because every tool agrees on the model, a script can set an interface description through NETCONF or RESTCONF and know exactly what field it is changing and what values are valid, without parsing CLI text.