# Set up local SDK previews

> Learn how to set up local SDK previews with Fern's --preview flag. Test generated SDK code locally before publishing to iterate quickly.

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:

```bash
# 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.

<Tip>
  `--preview` preserves any custom code you added to your SDK.
</Tip>

## Example usage

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

<Steps>
  ### Generator configuration

  ```yaml title="generators.yml" {4}
  api: 
    path: ./path/to/openapi.yml
  groups:
    python-sdk:
      generators:
        - name: fernapi/fern-python-sdk
          version: 4.48.1
          output:
            location: pypi
            package-name: imdb
            token: ${PYPI_TOKEN}
          github:
            repository: imdb/imdb-python
          config:
            client_class_name: imdb
  ```

  ### Invoke the Fern CLI

  ```shell
  fern generate --group python-sdk --preview
  ```

  ### Preview your SDK

  The resulting folder structure will look like this:

  <Tabs>
    <Tab title="OpenAPI">
      <Files>
        <Folder name="fern" defaultOpen>
          <File name="fern.config.json" />

          <Folder name=".preview" defaultOpen highlighted>
            <Folder name="fern-python-sdk" defaultOpen highlighted>
              <File name="..." highlighted />
            </Folder>
          </Folder>

          <File name="generators.yml" />

          <Folder name="openapi" defaultOpen>
            <File name="openapi.yml" />
          </Folder>
        </Folder>
      </Files>
    </Tab>

    <Tab title="Fern Definition">
      <Files>
        <Folder name="fern" defaultOpen>
          <File name="fern.config.json" />

          <Folder name=".preview" defaultOpen highlighted>
            <Folder name="fern-python-sdk" defaultOpen highlighted>
              <File name="..." highlighted />
            </Folder>
          </Folder>

          <File name="generators.yml" />

          <Folder name="definition" defaultOpen>
            <File name="api.yml" />

            <File name="imdb.yml" />
          </Folder>
        </Folder>
      </Files>
    </Tab>
  </Tabs>
</Steps>