OpenAPI Generator

The OpenAPI specification, or OAS, defines a standard, language-agnostic interface to HTTP APIs which allows both humans and computers to discover and understand the capabilities of the service.

This repository contains the source for the Fern generator that produces an OpenAPI specification:

• fernapi/fern-openapi

The generator is written in TypeScript and produces an OpenAPI 3.0.0 specification. If you have a need for Fern to generate a more recent specification version, let us know in this issue.

Fern handles transforming a Fern specification into Fern intermediate representation. IR is a normalized, Fern-specific definition of an API containing its endpoints, models, errors, authentication scheme, version, and more. Then the OpenAPI generator takes over and turns the IR into a production-ready OpenAPI specification.

Fern is an open source toolkit for designing, building, and consuming REST APIs. With Fern, you can generate client libraries, API documentation, and boilerplate for your backend server.

Head over to the official Fern website for more information, or head over to our Documentation to dive straight in and find out what Fern can do for you!

This generator is used via the Fern CLI by defining the OpenAPI generator:

- name: fernapi/openapi
  version: 0.0.28
  output:
    location: local-file-system
    path: ../../generated/openapi

By default, Fern runs the generators in the cloud. To run a generator on your local machine, use the --local flag for fern generate. This will run the generator locally in a Docker container, allowing you to inspect its logs and output. Read more.

You can customize the behavior of generators in generators.yml:

default-group: local
groups:
  local:
    generators:
      - name: fernapi/fern-openapi
        version: 0.0.27
        config: # <--
          format: json

Type: enum: 'json' | 'yaml'

Default: yaml

When configured, the generator outputs OAS files in the specified format.

Type: object

Default: {}

When configured, the object is merged into the generated OAS file. This allows you to add custom fields to the specification.

All generator releases are published in the Releases section of the GitHub repository. You can directly use these version numbers in your generator configuration files.

For instance, if you want to use version 0.0.27 of the OpenAPI generator:

default-group: local
groups:
  local:
    generators:
      - name: fernapi/fern-openapi
        version: 0.0.27
        output:
          location: local-file-system
          path: ../../generated/openapi

Fern will handle the rest automatically.

We greatly value community contributions. All the work on Fern generators happens right here on GitHub, both Fern developers and community contributors work together through submitting code via Pull Requests. See the contribution guidelines in CONTRIBUTING on how you can contribute to Fern!