Use Cases

This page shows typical use cases where endpoints4s can provide value.


Describe the HTTP APIs between the services, and let endpoints4s implement the clients and servers for these APIs:

source/** Application of a command.
  * Returns the produced event, or `None` in case of failure (aggregate
  * not found or invalid command).
val command: Endpoint[Command, Option[StoredEvent]] =
    post(path / "command", jsonRequest[Command]),

Invoking a service from another is as simple as a method call:

sourceval eventuallyMaybeEvent: IO[Option[StoredEvent]] =

endpoints4s takes care of correctly constructing the HTTP request and decoding the HTTP response according to the endpoint description.

Maintenance effort is reduced: you only maintain the description of the HTTP API, not its client and server implementations.

Web Applications

Thanks to Scala.js it is possible to write the client-side part of a web application in Scala. Then, endpoints4s simplifies client-server communication by turning method calls into remote invocations.

Example of endpoint definition:

source/** Registers a new meter */
val createMeter: Endpoint[CreateMeter, Meter] =
    post(metersPath, jsonRequest[CreateMeter]),

Corresponding invocation from the client-side:

sourceval eventuallyCreatedMeter: Future[Meter] =

Documenting a Web Service

Thanks to the separation between the description of an HTTP API and its implementation, endpoints4s can also generate an OpenAPI document for a given HTTP API description.

For instance, given the following endpoints descriptions:

sourceimport endpoints4s.{algebra, generic}

trait CounterEndpoints
    extends algebra.Endpoints
    with algebra.JsonEntitiesFromSchemas
    with generic.JsonSchemas {

  // HTTP endpoint for querying the current value of the counter. Uses the HTTP
  // verb ''GET'' and the path ''/counter''. Returns the current value of the counter
  // in a JSON object. (see below for the `counterJson` definition)
  val currentValue: Endpoint[Unit, Counter] =
    endpoint(get(path / "counter"), counterJsonResponse)

  // HTTP endpoint for updating the value of the counter. Uses the HTTP verb ''POST''
  // and the path ''/counter''. The request entity contains an `Operation` object encoded
  // in JSON. The endpoint returns the current value of the counter in a JSON object.
  val update: Endpoint[Operation, Counter] = endpoint(
      path / "counter",
      docs = Some("The operation to apply to the counter")

  // Since both the `currentValue` and `update` endpoints return the same
  // information, we define it once and just reuse it. Here, we say
  // that they return an HTTP response whose entity contains a JSON document
  // with the counter value
  lazy val counterJsonResponse: Response[Counter] =
    ok(jsonResponse[Counter], docs = Some("The counter current value"))

  // We generically derive a data type schema. This schema
  // describes that the case class `Counter` has one field
  // of type `Int` named “value”
  implicit lazy val jsonSchemaCounter: JsonSchema[Counter] = genericJsonSchema

  // Again, we generically derive a schema for the `Operation`
  // data type. This schema describes that `Operation` can be
  // either `Set` or `Add`, and that `Set` has one `Int` field
  // name `value`, and `Add` has one `Int` field named `delta`
  implicit lazy val jsonSchemaOperation: JsonSchema[Operation] =


endpoints4s can produce the following OpenApi document.