janstenpickle / trace4cats

Distributed app tracing implementation in pure scala using cats-effect

Version Matrix


Build & Release Maven Central Join the chat at https://gitter.im/trace4cats/community Scala Steward badge

Yet another distributed tracing system, this time just for Scala. Heavily relies upon Cats and Cats-effect.

Compatible with OpenTelemetry and Jaeger, based on, and interoperates wht Natchez.

Obligatory XKCD

For release information and changes see the releases page


It increasingly seems that Java tracing libraries are dependent on GRPC, which usually brings along lots of other dependencies. You may find Trace4Cats useful if you want to...

  • Reduce the number of dependencies in your application
  • Resolve a dependency conflict caused by a tracing implementation
  • Create a native-image using Graalvm


Trace4Cats supports publishing spans to the following systems:

Instrumentation for trace propagation and continuation is available for the following libraries

Unlike other tracing libraries, trace attributes are lazily evaluated. If a span is not sampled, no computation associated with calculating attribute values will be performed

For more information on how to use these can be found in the examples documentation


For more see the documentation for more advanced examples

Add the following dependencies to your build.sbt:

"io.janstenpickle" %% "trace4cats-core" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-inject" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-avro-exporter" % "0.12.0-RC1"

Then run the collector in span logging mode:

echo "log-spans: true" > /tmp/collector.yaml
docker run -p7777:7777 -p7777:7777/udp -it \
  -v /tmp/collector.yaml:/tmp/collector.yaml \
  janstenpickle/trace4cats-collector-lite:0.12.0-RC1 \

Finally, run the following code to export some spans to the collector:

import cats.data.Kleisli
import cats.effect._
import cats.implicits._
import org.typelevel.log4cats.Logger
import org.typelevel.log4cats.slf4j.Slf4jLogger
import io.janstenpickle.trace4cats.Span
import io.janstenpickle.trace4cats.`export`.CompleterConfig
import io.janstenpickle.trace4cats.avro.AvroSpanCompleter
import io.janstenpickle.trace4cats.inject.{EntryPoint, Trace}
import io.janstenpickle.trace4cats.kernel.SpanSampler
import io.janstenpickle.trace4cats.model.{SpanKind, SpanStatus, TraceProcess}

import scala.concurrent.duration._

object Trace4CatsQuickStart extends IOApp {
  def entryPoint[F[_]: Async: Logger](process: TraceProcess): Resource[F, EntryPoint[F]] =
    AvroSpanCompleter.udp[F](process, config = CompleterConfig(batchTimeout = 50.millis)).map { completer =>
      EntryPoint[F](SpanSampler.always[F], completer)

  def runF[F[_]: Sync: Trace]: F[Unit] =
    for {
      _ <- Trace[F].span("span1")(Sync[F].delay(println("trace this operation")))
      _ <- Trace[F].span("span2", SpanKind.Client)(Sync[F].delay(println("send some request")))
      _ <- Trace[F].span("span3", SpanKind.Client)(
        Trace[F].putAll("attribute1" -> "test", "attribute2" -> 200).flatMap { _ =>
    } yield ()

  override def run(args: List[String]): IO[ExitCode] =
    (for {
      implicit0(logger: Logger[IO]) <- Resource.eval(Slf4jLogger.create[IO])
      ep <- entryPoint[IO](TraceProcess("trace4cats"))
    } yield ep)
      .use { ep =>
        ep.root("this is the root span").use { span =>
          runF[Kleisli[IO, Span[IO], *]].run(span)


Trace4Cats is made up as both a set of libraries for integration in applications and standalone processes. For information on the libraries and interfaces see the design documentation.

The standalone components are the agent and the collector. To see how they work together, see the topologies documentation, for information on configuring and running the agent and collector see the components documentation.


SBT Dependencies

To use Trace4Cats within your application add the dependencies listed below as needed:

"io.janstenpickle" %% "trace4cats-core" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-inject" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-inject-zio" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-rate-sampling" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-fs2" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-http4s-client" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-http4s-server" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-sttp-client3" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-sttp-tapir" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-natchez" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-avro-exporter" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-avro-kafka-exporter" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-avro-kafka-consumer" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-jaeger-thrift-exporter" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-log-exporter" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-opentelemetry-otlp-grpc-exporter" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-opentelemetry-otlp-http-exporter" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-opentelemetry-jaeger-exporter" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-stackdriver-grpc-exporter" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-stackdriver-http-exporter" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-datadog-http-exporter" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-newrelic-http-exporter" % "0.12.0-RC1"
"io.janstenpickle" %% "trace4cats-zipkin-http-exporter" % "0.12.0-RC1"

native-image Compatibility

The following span completers have been found to be compatible with native-image:


This project supports the Scala Code of Conduct and aims that its channels (mailing list, Gitter, github, etc.) to be welcoming environments for everyone.