Status codes

To provide a (varying) status code of a server response, use the statusCode output, which maps to a value of type type tapir.model.StatusCode (which is an alias for Int). The tapir.model.StatusCodes object contains known status codes as constants. This type of output is used only when interpreting the endpoint as a server. If your endpoint returns varying status codes which you would like to have listed in documentation use statusCode.description(code1, "code1 description").description(code2, "code2 description") output.

Alternatively, a fixed status code can be specified using the statusCode(code) output.

Dynamic status codes

It is also possible to specify how status codes map to different outputs. All mappings should have a common supertype, which is also the type of the output. These mappings are used to determine the status code when interpreting an endpoint as a server, as well as when generating documentation and to deserialise client responses to the appropriate type, basing on the status code.

For example, below is a specification for an endpoint where the error output is a sealed trait ErrorInfo; such a specification can then be refined and reused for other endpoints:

sealed trait ErrorInfo
case class NotFound(what: String) extends ErrorInfo
case class Unauthorized(realm: String) extends ErrorInfo
case class Unknown(code: Int, msg: String) extends ErrorInfo
case object NoContent extends ErrorInfo

val baseEndpoint = endpoint.errorOut(
    statusMapping(StatusCode.NotFound, jsonBody[NotFound].description("not found")),
    statusMapping(StatusCode.Unauthorized, jsonBody[Unauthorized].description("unauthorized")),
    statusMapping(StatusCode.NoContent, => NoContent)(_ => ())),

Each mapping, defined using the statusMapping method is a case class, containing the output description as well as the status code. Moreover, default mappings can be defined using statusDefaultMapping:

  • for servers, the default status code for error outputs is 400, and for normal outputs 200 (unless a statusCode is used in the nested output)
  • for clients, a default mapping is a catch-all.

Both statusMapping and statusDefaultMapping return a value of type StatusMapping. A list of these values can be dynamically assembled (e.g. using a default set of cases, plus endpoint-specific mappings), and provided to oneOf.

Status mapping and type erasure

Sometime at runtime status mapping resolution can not work properly because of type erasure. For example this code will fail at startup type because of type erasure Right[NotFound] and Right[BadRequest] will become Right[Any], therefore the code would not be able to infer correct mapping for a value:

case class ServerError(what: String)

sealed trait UserError
case class BadRequest(what: String) extends UserError
case class NotFound(what: String) extends UserError

val baseEndpoint = endpoint.errorOut(
  oneOf[Either[ServerError, UserError]](
    statusMapping(StatusCode.NotFound, jsonBody[Right[ServerError, NotFound]].description("not found")),
    statusMapping(StatusCode.BadRequest, jsonBody[Right[ServerError, BadRequest]].description("unauthorized")),
    statusMapping(StatusCode.InternalServerError, jsonBody[Left[ServerError, UserError]].description("unauthorized")),

If you try this code, you will have the following error:

Exception in thread "main" java.lang.IllegalArgumentException: Constructing statusMapping on type Right[sttp.tapir.examples.TestTestExample.ServerError,sttp.tapir.examples.TestTestExample.NotFound] is not allowed because Right[sttp.tapir.examples.TestTestExample.ServerError,sttp.tapir.examples.TestTestExample.NotFound] is subject to type erasure, please use statusMappingValueMatcher instead

The solution is therefore to handwrite a function checking that a val (of type Any() is of the correct type:

val baseEndpoint = endpoint.errorOut(
  oneOf[Either[ServerError, UserError]](
    statusMappingValueMatcher(StatusCode.NotFound, jsonBody[Right[ServerError, NotFound]].description("not found")) {
      case Right(NotFound(_)) => true
    statusMappingValueMatcher(StatusCode.BadRequest, jsonBody[Right[ServerError, BadRequest]].description("unauthorized")) {
      case Right(BadRequest(_)) => true
    statusMappingValueMatcher(StatusCode.InternalServerError, jsonBody[Left[ServerError, UserError]].description("unauthorized")) {
      case Left(ServerError(_)) => true

Of course you could use statusMappingValueMatcher to do runtime filtering for other purpose than solving type erasure.

In the case of solving type erasure, writing by hand partial function to match value against composition of case class and sealed trait can be repetitive. To make that more easy, we provide an experimental typeclass - MatchType - so you can automatically derive that partial function:

import sttp.tapir.typelevel.MatchType

val baseEndpoint = endpoint.errorOut(
  oneOf[Either[ServerError, UserError]](
    statusMappingFromMatchType(StatusCode.NotFound, jsonBody[Right[ServerError, NotFound]].description("not found")),
    statusMappingFromMatchType(StatusCode.BadRequest, jsonBody[Right[ServerError, BadRequest]].description("unauthorized")),
    statusMappingFromMatchType(StatusCode.InternalServerError, jsonBody[Left[ServerError, UserError]].description("unauthorized"))

Server interpreters

Unless specified otherwise, successful responses are returned with the 200 OK status code, and errors with 400 Bad Request. For exception and decode failure handling, see error handling.