circe AutoDerivation // http://immutables.pl/2017/02/25/customizing-circes-auto-generic-derivation/

autoderivation.scala

case class Foo(fooId: Int, fooName: String)
object Foo extends io.circe.generic.AutoDerivation

case class Bar(barId: Int, barName: String)
object Bar {
  import io.circe.Encoder
  import io.circe.generic.semiauto._
  import io.circe.generic.extras.Configuration

  implicit val config: Configuration = Configuration.default.withSnakeCaseMemberNames
  implicit val encoder: Encoder[Bar] = deriveEncoder[Bar]
}

case class Baz(id: Int, name: String)
object Baz {
  import io.circe.Encoder

  implicit val encoder: Encoder[Baz] =
    Encoder.forProduct2("baz-id", "baz-name")(b => (b.id, b.name))
}

object Main extends App {
  import io.circe.syntax._

  println(Foo(1, "name").asJson.noSpaces)
  println(Bar(2, "name").asJson.noSpaces)
  println(Baz(3, "name").asJson.noSpaces)
}