Tuple2Format.scala

import play.api.libs.json._
import play.api.libs.functional.syntax._
import play.api.data.validation._

implicit def tuple2Reads[A, B](implicit aReads: Reads[A], bReads: Reads[B]): Reads[Tuple2[A, B]] = Reads[Tuple2[A, B]] {
  case JsArray(arr) if arr.size == 2 => for {
    a <- aReads.reads(arr(0))
    b <- bReads.reads(arr(1))
  } yield (a, b)
  case _ => JsError(Seq(JsPath() -> Seq(ValidationError("Expected array of two elements"))))
}

implicit def tuple2Writes[A, B](implicit aWrites: Writes[A], bWrites: Writes[B]): Writes[Tuple2[A, B]] = new Writes[Tuple2[A, B]] {
  def writes(tuple: Tuple2[A, B]) = JsArray(Seq(aWrites.writes(tuple._1), bWrites.writes(tuple._2)))
}