trace4cats / trace4cats   0.14.7

MIT License GitHub

Distributed app tracing implementation in pure scala using cats-effect

Scala versions: 3.x 2.13 2.12


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⚠️ If you are upgrading to 0.14.0 please read the migration guide.

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 with 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.

More information on how to use these can be found in the examples documentation.


For more see the documentation and more advanced examples.

Add the following dependencies to your build.sbt:

"io.janstenpickle" %% "trace4cats-core" % "0.14.0"
"io.janstenpickle" %% "trace4cats-avro-exporter" % "0.14.0"

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:0.14.0 \

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

import cats.Monad
import cats.effect._
import cats.effect.std.Console
import cats.implicits._
import trace4cats._
import trace4cats.avro.AvroSpanCompleter

import scala.concurrent.duration._

object Trace4CatsQuickStart extends IOApp.Simple {
  def entryPoint[F[_]: Async](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[_]: Monad: Console: Trace]: F[Unit] =
    for {
      _ <- Trace[F].span("span1")(Console[F].println("trace this operation"))
      _ <- Trace[F].span("span2", SpanKind.Client)(Console[F].println("send some request"))
      _ <- Trace[F].span("span3", SpanKind.Client)(
        Trace[F].putAll("attribute1" -> "test", "attribute2" -> 200) >>
    } yield ()

  def run: IO[Unit] =
    entryPoint[IO](TraceProcess("trace4cats")).use { ep =>
      ep.root("this is the root span").use { span =>
        runF[Kleisli[IO, Span[IO], *]].run(span)

Migrating to 0.14.0

Version 0.14.0 introduced a reworked module and package structure that reduced the number of dependencies and imports required to get started quickly. Effectively import trace4cats._ is all you should need to import throughout most of your codebase.

See the migration guide for information on how to migrate.


Trace4Cats is separated into a few repositories:


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.

The source code for these components is located in the trace4cats-components repository.


SBT Dependencies

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

"io.janstenpickle" %% "trace4cats-core" % "0.14.0"
"io.janstenpickle" %% "trace4cats-rate-sampling" % "0.14.0"
"io.janstenpickle" %% "trace4cats-fs2" % "0.14.0"
"io.janstenpickle" %% "trace4cats-http4s-client" % "0.14.0"
"io.janstenpickle" %% "trace4cats-http4s-server" % "0.14.0"
"io.janstenpickle" %% "trace4cats-sttp-client3" % "0.14.0"
"io.janstenpickle" %% "trace4cats-sttp-tapir" % "0.14.0"
"io.janstenpickle" %% "trace4cats-natchez" % "0.14.0"
"io.janstenpickle" %% "trace4cats-avro-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-avro-kafka-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-avro-kafka-consumer" % "0.14.0"
"io.janstenpickle" %% "trace4cats-jaeger-thrift-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-opentelemetry-otlp-grpc-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-opentelemetry-otlp-http-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-opentelemetry-jaeger-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-stackdriver-grpc-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-stackdriver-http-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-datadog-http-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-newrelic-http-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-zipkin-http-exporter" % "0.14.0"

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.