GeneratorsTypeScript

Generating an SDK

View as Markdown

Generate a TypeScript SDK by following the instructions on this page.

Already completed the Quickstart? Skip ahead to Set up GitHub repositories.

1

Install the Fern CLI

$npm install -g fern-api
2

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>

OpenAPI accepts both JSON and YAML formats.

This creates a fern folder in your current directory.

fern
fern.config.json# root-level configuration
generators.yml# generators and API spec configuration
3

Validate your API definition

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

$fern check
4

Add the SDK generator

Run the following command to add the TypeScript SDK generator to generators.yml:

$fern add fern-typescript-sdk --group {{GROUP_NAME}}

This command adds the following group to generators.yml:

generators.yml
1  ts-sdk: # group name
2    generators:
3      - name: fern-typescript-sdk
4        version: 3.72.2
5        output:
6          location: local-file-system
7          path: ../sdks/typescript

fern init includes a TypeScript SDK generator by default. If you already ran fern init and haven’t modified generators.yml, you can skip this step.

5

Generate the SDK

Run the following command to generate your SDK:

$fern generate --group ts-sdk

If you have multiple APIs, use the --api flag to specify the API you want to generate:

$fern generate --group ts-sdk --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:

fern# created by fern init
sdks# created by fern generate --group ts-sdk
typescript
Client.ts
index.ts
errors
core
api
6

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-typescript-sdk).
  3. Install the Fern GitHub App on both repositories.
7

Publish to npm

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