gemini-hlsw / clue

GraphQL client for Scala.

Version Matrix


Experimental GraphQL client.


1) Create a client


  • A GraphQLClient[F[_], S] (supporting queries and mutations), or
  • A GraphQLStreamingClient[F[_], S] (supporting queries, mutations and subscriptions).

S is a type denoting the schema. It can be any type, even a phantom type. It's only used to type-match clients and operations.


  import clue._
  import clue.js._
  import cats.effect.IO
  import io.chrisdavenport.log4cats.Logger

  sealed trait StarWars

  implicit val backend: Backend[IO] = AjaxJSBackend[IO]
  val oneShotClient: GraphQLClient[IO, StarWars] = HttpClient.of[IO, Schema]("")

  implicit val streamingBackend: StreamingBackend[IO] = WebSocketJSBackend[IO]
  val streamingClient: GraphQLStreamingClient[IO, StarWars] = ApolloStreamingClient.of[IO, Schema]("wss://")


  • ApolloStreamingClient implements the de facto Apollo protocol for streaming over web sockets.
  • The HttpClient.of constructor requires an implicit instance of a Backend[F]. An AjaxJSBackend[F] is provided for Scala.js.
  • The ApolloStreamingClient.of constructor requires an implicit instance of a StreamingBackend[F]. A WebSocketJSBackend[F] is provided for Scala.js.

2) Create operations

They must extend GraphQLOperation[S], defining the following members:

  val document: String

  type Variables
  type Data

  val varEncoder: io.circe.Encoder[Variables]
  val dataDecoder: io.circe.Decoder[Data]


  import io.circe._
  import io.circe.generic.semiauto._

  object CharacterQuery extends GraphQLOperation[StarWars] {
    val document = """
        query (charId: ID!) {
          character(id: $charId) {

    case class Variables(charId: String)

    case class Character(id: String, name: Option[String])
    object Character {
      implicit val characterDecoder: Decoder[Character] = deriveDecoder[Character]

    case class Data(character: Option[Character])

    val varEncoder: Encoder[Variables] = deriveEncoder[Variables]
    val dataDecoder: Decoder[Data] = deriveDecoder[Data]

3) Invoke operations



# Data(Some(Character("0001", Some("Luke"))))