Set up local SDK previews | Fern Documentation

You're viewing the legacy SDK docs

These pages cover SDK generation configured with generators.yml. New projects use sdk-config.yml, so see the Current version of this page for up-to-date guidance. To move an existing project, follow the SDK Config migration guide, which walks through fern sdk migrate, and review the sdk-config.yml reference.

Once you configure your SDK, you can use the --preview flag to test generated SDK code locally before publishing. This allows quick iteration on your SDK as you develop:

# Preview all SDKs
fern generate --preview
# Preview SDK for a specific language
fern generate --group <language>-sdk --preview

--preview generates your SDK code into a local .preview/ folder within your fern folder. No changes are published to package managers or GitHub.

--preview preserves any custom code you added to your SDK.

Example usage

Here’s an example of how you can preview a Python SDK.

Generator configuration

generators.yml

api: 
  path: ./path/to/openapi.yml
groups:
  python-sdk:
    generators:
      - name: fern-python-sdk
        version: 5.41.4
        output:
          location: pypi
          package-name: imdb
          token: ${PYPI_TOKEN}
        github:
          repository: imdb/imdb-python
        config:
          client_class_name: imdb

Invoke the Fern CLI

fern generate --group python-sdk --preview

Preview your SDK

The resulting folder structure will look like this:

fern

fern.config.json

.preview

fern-python-sdk

...

generators.yml

openapi

openapi.yml