Contributing Guidelines

There are two main ways to contribute to the project — submitting issues and submitting fixes/changes/improvements via pull requests.

Submitting issues

Both bug reports and feature requests are welcome. Submit issues here.

  • Search for existing issues to avoid reporting duplicates.
  • When submitting a bug report:
    • Test it against the most recently released version. It might have been already fixed.
    • By default, we assume that your problem reproduces in Kotlin/JVM. Please, mention if the problem is specific to Kotlin/JS or Kotlin/Native.
    • Include the code that reproduces the problem. Provide the complete reproducer code, yet minimize it as much as possible.
    • However, don't put off reporting any weird or rarely appearing issues just because you cannot consistently reproduce them.
    • If the bug is in behavior, then explain what behavior you‘ve expected and what you’ve got.
  • When submitting a feature request:
    • Explain why you need the feature — what‘s your use-case, what’s your domain.
    • Explaining the problem you face is more important than suggesting a solution. Report your problem even if you don't have any proposed solution.
    • If there is an alternative way to do what you need, then show the code of the alternative.

Submitting PRs

We love PRs. Submit PRs here. However, please keep in mind that maintainers will have to support the resulting code of the project, so do familiarize yourself with the following guidelines.

  • All development (both new features and bug fixes) is performed in the develop branch.
    • The master branch always contains sources of the most recently released version.
    • Base PRs against the develop branch.
    • The develop branch is pushed to the master branch during release.
    • Documentation in markdown files can be updated directly in the master branch, unless the documentation is in the source code, and the patch changes line numbers.
  • If you fix documentation:
    • After fixing/changing code examples in the docs folder or updating any references in the markdown files run the Knit tool and commit the resulting changes as well. It will not pass the tests otherwise.
    • If you plan extensive rewrites/additions to the docs, then please contact the maintainers to coordinate the work in advance.
  • If you make any code changes:
  • If you fix a bug:
    • Write the test that reproduces the bug.
    • Fixes without tests are accepted only in exceptional circumstances if it can be shown that writing the corresponding test is too hard or otherwise impractical.
    • Follow the style of writing tests that is used in this project: name test functions as testXxx. Don't use backticks in test names.
  • If you introduce any new public APIs:
    • All new APIs must come with documentation and tests.
    • All new APIs are initially released with @ExperimentalCoroutineApi annotation and are graduated later.
    • Update the public API dumps and commit the resulting changes as well. It will not pass the tests otherwise.
    • If you plan large API additions, then please start by submitting an issue with the proposed API design
      to gather community feedback.
    • Contact the maintainers to coordinate any big piece of work in advance.
  • Comment on the existing issue if you want to work on it. Ensure that the issue not only describes a problem, but also describes a solution that had received a positive feedback. Propose a solution if there isn't any.
  • Steps for contributing new integration modules are explained here.


This library is built with Gradle.

  • Run ./gradlew build to build. It also runs all the tests.
  • Run ./gradlew <module>:test to test the module you are looking at to speed things up during development.
  • Run ./gradlew jvmTest to perform only fast JVM tests of the core multiplatform module.

You can import this project into IDEA, but you have to delegate build actions to Gradle (in Preferences -> Build, Execution, Deployment -> Build Tools -> Gradle -> Runner)

Environment requirements

  • JDK >= 11 referred to by the JAVA_HOME environment variable.
  • JDK 1.6 referred to by the JDK_16 environment variable. It is OK to have JDK_16 pointing to a non 1.6 JDK (e.g. JAVA_HOME) for external contributions.
  • JDK 1.8 referred to by the JDK_18 environment variable. Only used by nightly stress-tests. It is OK to have JDK_18 to a non 1.8 JDK (e.g. JAVA_HOME) for external contributions.

For external contributions you can for example add this to your shell startup scripts (e.g. ~/.zshrc):

# This assumes JAVA_HOME is set already to a JDK >= 11 version
export JDK_16="$JAVA_HOME"
export JDK_18="$JAVA_HOME"

Running the Knit tool

  • Use Knit for updates to documentation:
    • Run ./gradlew knit to update example files, links, tables of content.
    • Commit updated documents and examples together with other changes.

Updating the public API dump

  • Use Binary Compatibility Validator for updates to public API:
    • Run ./gradlew apiDump to update API index files.
    • Commit updated API indexes together with other changes.


  • Full release procedure checklist is here.

Contacting maintainers

  • If something cannot be done, not convenient, or does not work — submit an issue.
  • “How to do something” questions — StackOverflow.
  • Discussions and general inquiries — use #coroutines channel in KotlinLang Slack.