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Zally: A minimalistic, simple-to-use OpenAPI 2 and 3 linter

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Zally is a quality assurance tool. It's a linter for OpenAPI specifications, it performs the following tasks :

  • Increases the quality of APIs
  • Checks compliance
  • Delivers early feedback for API designers
  • Ensures the same look-and-feel of APIs
  • Supports API-First approach
  • Provides best practices and advices

Its standard configuration will check your APIs against the rules defined in Zalando's RESTful Guidelines, but anyone can use it out-of-the-box.

Zally has an easy-to-use CLI which uses the server in the background so that you can check your API on the spot. It also features an intuitive Web UI that shows implemented rules and lints external files and (with its online editor) API definitions.


  • Support for OpenAPI 3 and (Swagger) OpenAPI 2 specifications
  • RESTful API, CLI and Web interface
  • Rich Check configuration
  • Ignore functionality (x-zally-ignore extension)
  • Java/Kotlin API for new Checks + helper functions

Quick start guide

Trying out Zally is easy. You can build and run the whole Zally stack (web-ui, server and database) by executing:

docker compose up -d

Web UI is accessible on http://localhost:8080; Zally server on http://localhost:8000

Documentation and Manuals

Please consult the following documents for further information:


Contributing to Zally

Zally welcomes contributions from the open source community. To get started, take a look at our contributing guidelines. Then check our Project Board and Issues Tracker for ideas.


Feel free to join our Gitter room or contact one of the maintainers directly.


Zally is not the only linter for OpenAPI v2 and v3. There is an article comparing different OpenAPI linters.

So why should you choose Zally?

  • It supports Zalando's RESTful Guidelines
  • It can be used in multiple ways: RESTful API, CLI and Web interface
  • Highly customizable (with Kotlin)


MIT license with an exception. See license file.




  1. Create a separate branch with a name release-<release-version>.

  2. Update current version in server/ from -SNAPSHOT to a final version.

  3. Update mime types configuration:

       ./gradlew -q generate-media-types-config --info
  4. Commit the updated file to the repository.

  5. Release Zally server and API using the command

    cd server
    ./gradlew clean build publishAllPublicationsToMavenRepository
  6. Commit server/ with the release version

  7. Create a tag

    git tag v<release-version> -m "Version <release-version>"
  8. Bump version in server/ to the next -SNAPSHOT

  9. Push release branch and tag

     git push origin
     git push origin <tag-name>
  10. Create a Pull Request with the version update

  11. Create and publish a release with a new version in GitHub