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OpenAPI Generator turns an OpenAPI definition into API client libraries, server stubs, documentation, or configuration. To generate code, install the CLI, choose a generator that matches your target language and runtime, then run openapi-generator-cli generate with your specification file, generator name, and output directory.
What OpenAPI Generator does
OpenAPI Generator is an open-source code-generation tool for OpenAPI Specification 2.0 and 3.0 documents. It can produce API client libraries, server stubs, documentation, and configuration. It generates a starting point from your specification; the specific language, framework, and output behavior depend on the generator you select.
Install the CLI
The official installation guide documents several ways to run OpenAPI Generator. The npm package is a wrapper, not a way to avoid the Java prerequisite: the documented npm route still requires Java.
- npm: Run
npm install @openapitools/openapi-generator-cli -g. This installs the command-line wrapper globally; Java is still required. - JBang: Run
jbang --java 11 org.openapitools:openapi-generator-cli:LATEST help. - JAR: Download the CLI JAR, then run
java -jar openapi-generator-cli.jar help. - Bash launcher: The launcher checks the GitHub repository for the latest release. Set
OPENAPI_GENERATOR_VERSIONto pin the version rather than relying on an unpinned latest release.
For repeatable local work and CI, select and pin a version so the same generator is used across runs. See the official installation options.
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Generate code from an OpenAPI file
Once the CLI is available, use generate with an input specification, a generator identifier, and an output directory:
openapi-generator-cli generate
-i openapi.yaml
-g <generator-name>
-o generated/Replace openapi.yaml with your specification path, <generator-name> with the generator you chose, and generated/ with the destination directory. The output is generated code or other artifacts appropriate to that generator.
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Find commands and generator names
openapi-generator-cli helplists commands and options.openapi-generator-cli listshows available generators.openapi-generator-cli config-help -g <generator-name>displays settings for a particular generator.
The tool also includes batch for external generation configurations, and author and meta for generator and template work. The usage guide covers the command-line workflow.
Choose the right generator
OpenAPI Generator supports client and server generators for languages and ecosystems including Java, Kotlin, C#, Python, JavaScript and TypeScript, Go, Rust, Swift, PHP, and Ruby. Choose by more than language alone:
- Target language and runtime: Confirm that the generated code fits the language version and runtime your project uses.
- Client library or server framework: Where multiple generators exist for a language, choose the library or framework that matches your application.
- Generated behavior: Review the API style and how the output handles serialization and authentication.
- Stability: Check the generator and its options before making it part of a recurring build.
- Project fit: Make sure the output follows repository conventions and can be regenerated without overwriting unrelated work.
Generator-specific options can be passed as CLI additional properties or configured through Maven and Gradle integrations. Use config-help for the generator you plan to run rather than assuming options are interchangeable.
Use OpenAPI Generator in GitHub Actions
The project documents GitHub workflow integration. For a maintainable team setup, keep the OpenAPI document and generator version under version control, write output to a predictable directory, and review generated diffs. Configure CI to fail when regeneration produces unexpected changes; that makes drift visible rather than silently leaving checked-in output out of sync with the specification.
The integrations documentation covers supported integration approaches, including GitHub workflows. Pinning the version is especially important in CI: an unpinned latest release can change generated output between runs.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Customize generated output
If the closest maintained generator needs changes, first investigate its configuration and template overrides. This is usually a more contained starting point than building a generator from scratch. For a wholly new generator, the project documents generator creation and provides a new.sh scaffolding helper; see the customization documentation.
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