idiomatic Go (golang) validation package.

 ozzo-validation is a Go package that provides configurable and extensible
 data validation capabilities. It has the following features:
 .
  * use normal programming constructs rather than error-prone struct tags
    to specify how data should be validated.
  * can validate data of different types, e.g., structs, strings, byte
    slices, slices, maps, arrays.
  * can validate custom data types as long as they implement the
    Validatable interface.
  * can validate data types that implement the sql.Valuer interface (e.g.
    sql.NullString).
  * customizable and well-formatted validation errors.
  * error code and message translation support.
  * provide a rich set of validation rules right out of box.
  * extremely easy to create and use custom validation rules.