Skip to main content

Quick Start

Below is a quick example of smithy4s in action. This page does not provide much explanation or detail. For more information on various aspects of smithy4s, read through the other sections of this documentation site.

For sbt

This section will get you started with a simple sbt module that enables smithy4s code generation. For a similar setup for mill, see Mill below.


Add the smithy4s-sbt-codegen plugin to your build.

addSbtPlugin("com.disneystreaming.smithy4s" % "smithy4s-sbt-codegen" % "0.18.19")


Enable the plugin in your project, add the smithy and http4s dependencies.

import smithy4s.codegen.Smithy4sCodegenPlugin

ThisBuild / scalaVersion := "2.13.12"

val example = project
libraryDependencies ++= Seq(
"com.disneystreaming.smithy4s" %% "smithy4s-http4s" % smithy4sVersion.value,
"com.disneystreaming.smithy4s" %% "smithy4s-http4s-swagger" % smithy4sVersion.value,
"org.http4s" %% "http4s-ember-server" % "0.23.26"

For Mill

This section will get you started with a mill module with code generation enabled on it.

In your

import $ivy.`com.disneystreaming.smithy4s::smithy4s-mill-codegen-plugin::0.18.19`
import smithy4s.codegen.mill._

import mill._, mill.scalalib._
object example extends ScalaModule with Smithy4sModule {
def scalaVersion = "2.13.8"
override def ivyDeps = Agg(

Smithy content

Now is the time to add some Smithy shapes to see what code generation can do for you. Following the setup above, the location for the Smithy content will change depending on what build tool you used.

Now let's define an API in Smithy. Create the following file:

  • for sbt, you'll write in modules/example/src/main/smithy/ExampleService.smithy.
  • for mill, you'll write in example/smithy/ExampleService.smithy

And add the content below:

namespace smithy4s.hello

use alloy#simpleRestJson

service HelloWorldService {
version: "1.0.0",
operations: [Hello]

@http(method: "POST", uri: "/{name}", code: 200)
operation Hello {
input: Person,
output: Greeting

structure Person {
name: String,

town: String

structure Greeting {
message: String

The Scala code corresponding to this smithy file will be generated the next time you compile your project.

Using the generated code

Now, let's use the generated code by the service. You need to create a scala file at the following location:

  • for sbt modules/example/src/main/scala/Main.scala
  • for mill example/src/Main.scala

Implement your service by extending the generated Service trait. Wire up routes into server.

import smithy4s.example.hello._
import cats.effect._
import cats.implicits._
import org.http4s.implicits._
import org.http4s.ember.server._
import org.http4s._
import smithy4s.http4s.SimpleRestJsonBuilder

object HelloWorldImpl extends HelloWorldService[IO] {
def hello(name: String, town: Option[String]): IO[Greeting] = IO.pure {
town match {
case None => Greeting(s"Hello $name!")
case Some(t) => Greeting(s"Hello $name from $t!")

object Routes {
private val example: Resource[IO, HttpRoutes[IO]] =

private val docs: HttpRoutes[IO] =[IO](HelloWorldService)

val all: Resource[IO, HttpRoutes[IO]] = <+> docs)

object Main extends IOApp.Simple {

val run = Routes.all
.flatMap { routes =>
.use(_ => IO.never)


Run Service

  • for sbt: sbt "example/run"
  • for mill: mill

Here you will find the automatically generated SwaggerUI which will allow you to easily test your API.

SwaggerUI documentation site request

SwaggerUI documentation site response

Client Example

You can also generate a client using smithy4s.

import org.http4s.ember.client.EmberClientBuilder

object ClientImpl extends IOApp.Simple {

val helloWorldClient: Resource[IO, HelloWorldService[IO]] = for {
client <- EmberClientBuilder.default[IO].build
helloClient <- SimpleRestJsonBuilder(HelloWorldService)
} yield helloClient

val run = helloWorldClient.use(c =>
c.hello("Sam", Some("New York City"))
.flatMap(greeting => IO.println(greeting.message))