Generating an SDK

Install the Fern CLI

npm install -g fern-api

Initialize the fern folder

Initialize the fern folder with your existing OpenAPI specification. Specify your organization name using the --organization flag.

fern init --openapi path/to/openapi.yml \
--organization <YourOrganization>

This creates a fern folder in your current directory.

Validate your API definition

Check that your API definition is valid, and fix errors before proceeding:

fern check

Add the SDK target

Add a Ruby target to the targets list in sdk-config.yml:

targets:
  - language: ruby
    output:
      delivery: files
      path: ../sdks/ruby

The target uses the newest supported Ruby generator. To pin a version, set generatorVersion on the target.

Generate the SDK

Run the following command to generate your SDK:

fern generate --target ruby

fern generate --target ruby --api your-api-name

The first time you run fern generate, you must log in. Confirm the prompt and choose any of the login methods to authenticate, then generation continues automatically.

fern generate creates a sdks folder in your current directory. The resulting folder structure looks like this:

Set up GitHub repositories

Fern uses a multi-repo structure: your source repository contains the fern/ folder, and each SDK gets its own separate repository.

1. Create a source repository for your fern/ folder if you don’t have one already (e.g., your-org/your-api-definitions).
2. Create an SDK repository for your SDK (e.g., your-org/your-api-ruby-sdk).
3. Install the Fern GitHub App on both repositories.

Publish to RubyGems

Follow the Publishing to RubyGems guide to configure your gem and set up automated publishing via GitHub Actions.