Map[String, T] work as you expect.

Note that you need a JsonRW[T] given instance.

        Map(
            "a" -> 5,
            "b" -> 123
        ).toJson
        // {"a":5,"b":123}
        

        """ {"a":5,"b":123} """.parseJson[Map[String, Int]]
        // Map(a -> 5, b -> 123)
        

Maps are limited in the sense that the values have to be of same type.
If you need them different, consider using case classes or dynamic JSON values.