Metrics collection is possible by creating Metric instances and adding them to server options via MetricsInterceptor. Certain endpoints can be ignored by adding their definitions to ignoreEndpoints list.

Metric wraps an aggregation object (like a counter or gauge), and needs to implement the onRequest function, which returns an EndpointMetric instance.

Metric.onRequest is used to create the proper metric description. Any additional data might be gathered there, like getting current timestamp and passing it down to EndpointMetric callbacks which are then executed in certain points of request processing.

There are three callbacks in EndpointMetric:

  1. onEndpointRequest - called after a request matches an endpoint (inputs are successfully decoded), or when decoding inputs fails, but a downstream interceptor provides a response.
  2. onResponse - called after response is assembled. Note that the response body might be lazily produced. To properly observe end-of-body, use the provided BodyListener.
  3. onException - called after exception is thrown (in underlying streamed body, and/or on any other exception when there’s no default response)


By default, request metrics are labeled by path and method. Response labels are additionally labelled by status code group. For example GET endpoint like http://h:p/api/persons?name=Mike returning 200 response will be labeled as path="api/persons", method="GET", status="2xx". Query params are omitted by default, but it’s possible to include them as shown in example below.

If the path contains captures, the label will include the path capture name instead of the actual value, e.g. api/persons/{name}.

Labels for default metrics can be customized, any attribute from Endpoint, ServerRequest and ServerResponse could be used, for example:

import sttp.tapir.metrics.MetricLabels

val labels = MetricLabels(
  forRequest = Seq(
    "path" -> { case (ep, _) => ep.renderPathTemplate() },
    "protocol" -> { case (_, req) => req.protocol }
  forResponse = Seq()

Prometheus metrics

Add the following dependency:

"com.softwaremill.sttp.tapir" %% "tapir-prometheus-metrics" % "0.18.0-M10"

PrometheusMetrics encapsulates CollectorReqistry and Metric instances. It provides several ready to use metrics as well as an endpoint definition to read the metrics & expose them to the Prometheus server.

For example, using AkkaServerInterpeter:

import akka.http.scaladsl.server.Route
import io.prometheus.client.CollectorRegistry
import sttp.monad.FutureMonad
import sttp.tapir.metrics.prometheus.PrometheusMetrics
import sttp.tapir.server.akkahttp.{AkkaHttpServerInterpreter, AkkaHttpServerOptions}

import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.Future

implicit val monad: FutureMonad = new FutureMonad()

val prometheusMetrics = PrometheusMetrics[Future]("tapir", CollectorRegistry.defaultRegistry)

implicit val serverOptions: AkkaHttpServerOptions =
  AkkaHttpServerOptions.customInterceptors(metricsInterceptor = Some(prometheusMetrics.metricsInterceptor()))

val routes: Route = AkkaHttpServerInterpreter.toRoute(prometheusMetrics.metricsEndpoint)

Custom metrics

Also, custom metric creation is possible and attaching it to PrometheusMetrics, for example:

import sttp.tapir.metrics.prometheus.PrometheusMetrics
import sttp.tapir.metrics.{EndpointMetric, Metric}
import io.prometheus.client.{CollectorRegistry, Counter}
import scala.concurrent.Future

// Metric for counting responses labeled by path, method and status code
val responsesTotal = Metric[Future, Counter](
    .help("HTTP responses")
    .labelNames("path", "method", "status")
  onRequest = { (req, counter, _) =>
        .onResponse { (ep, res) =>
          Future.successful {
            val path = ep.renderPathTemplate()
            val method = req.method.method
            val status = res.code.toString()
            counter.labels(path, method, status).inc()

val prometheusMetrics = PrometheusMetrics[Future]("tapir", CollectorRegistry.defaultRegistry).withCustom(responsesTotal)

OpenTelemetry metrics

Add the following dependency:

"com.softwaremill.sttp.tapir" %% "tapir-opentelemetry-metrics" % "0.18.0-M10"

OpenTelemetry metrics are vendor-agnostic and can be exported using one of exporters from SDK.

OpenTelemetryMetrics encapsulates metric instances and needs a MetricProvider from OpenTelemetry SDK to create default metrics, simply:

import sttp.tapir.metrics.opentelemetry.OpenTelemetryMetrics
import io.opentelemetry.api.metrics.MeterProvider
import scala.concurrent.Future

val provider: MeterProvider = ???

val metrics = OpenTelemetryMetrics[Future](provider, "your-app-instrumentation", "1.0.0")

val metricsInterceptor = metrics.metricsInterceptor() // add me to your server options