Publishing to crates.io | Fern Documentation

Enterprise feature

This feature is available only for the Enterprise plan. To get started, reach out to support@buildwithfern.com.

Publish your public-facing Fern Rust SDK to the crates.io registry. After following the steps on this page, you’ll have a versioned crate published on crates.io. To distribute the SDK internally instead, generate to the local file system (optionally self-hosted) and build a .crate file with fern generate --package.

This page assumes that you have:

An initialized fern folder, a GitHub repository for your Rust SDK, and a Rust target in sdk-config.yml. See Generating an SDK (Rust).

Versioned package published on crates.io

Configure `sdk-config.yml`

Update the Rust target in sdk-config.yml to configure the crate name, client name, and publishing destination. Your sdk-config.yml should live in your source repository (or on your local machine), not the repository that contains your Rust SDK code.

Add a unique crate name

Your crate name must be unique in the crates.io registry, otherwise publishing your SDK will fail.

sdk-config.yml

targets:
  - language: rust
    package:
      packageName: your-crate-name

Configure the client name

The generation.naming.clientName option controls the name of the generated client struct. This is the name users will use when instantiating your SDK client.

sdk-config.yml

targets:
  - language: rust
    package:
      packageName: your-crate-name
    generation:
      naming:
        clientName: YourClientName

Configure GitHub delivery and crates.io publishing

Set output.delivery to github, add the path to your GitHub repository, and set output.publish.registry to crates:

sdk-config.yml

targets:
  - language: rust
    package:
      packageName: your-crate-name
    generation:
      naming:
        clientName: YourClientName
    output:
      delivery: github
      github:
        repository: your-org/company-rust
      publish:
        registry: crates

Set up crates.io publishing authentication

Log into crates.io

Log into crates.io using your GitHub account.

Navigate to Account settings

Click on your profile picture in the top right corner.
Select Account Settings.
Go to the API Tokens section.

Create a new API token

Click New Token.
Name your token (e.g., “Fern SDK Publishing”).
Under Scopes, select publish-new to publish new crates and publish-update to update existing crates.
Click Generate Token.

Save your new token immediately. It won’t be displayed again after you leave the page.

Configure crates.io authentication token

Add token: ${CRATES_IO_API_KEY} to output.publish to tell Fern to use the CRATES_IO_API_KEY environment variable for authentication when publishing to crates.io.

sdk-config.yml

targets:
  - language: rust
    package:
      packageName: your-crate-name
    generation:
      naming:
        clientName: YourClientName
    output:
      delivery: github
      github:
        repository: your-org/company-rust
      publish:
        registry: crates
        token: ${CRATES_IO_API_KEY}

Publish your SDK

Decide how you want to publish your SDK to crates.io. You can use GitHub workflows for automated releases or publish directly via the CLI.

Release via a GitHub workflow (recommended)

Set up a release workflow via GitHub Actions so you can trigger new SDK releases directly from your source repository.

Set up authentication

Open your source repository in GitHub. Click on the Settings tab in your repository. Then, under the Security section, open Secrets and variables > Actions.

You can also use the url https://github.com/<your-repo>/settings/secrets/actions.

Add secret for your crates.io token

Select New repository secret.
Name your secret CRATES_IO_API_KEY.
Add the corresponding token you generated above.
Click Add secret.

Add secret for your Fern API key

Select New repository secret.
Name your secret FERN_TOKEN.
Add your Fern API key. If you don’t already have one, generate one by running fern token. By default, the API key is generated for the organization listed in fern.config.json.
Click Add secret.

Set up a new workflow

Set up a CI workflow that you can manually trigger from the GitHub UI. In your repository, navigate to Actions. Select New workflow, then Set up workflow yourself. Add a workflow that’s similar to this:

.github/workflows/publish.yml

name: Publish Rust SDK
on:
workflow_dispatch:
  inputs:
    version:
      description: "The version of the Rust SDK that you would like to release"
      required: true
      type: string
jobs:
release:
  runs-on: ubuntu-latest
  steps:
    - name: Checkout repo
      uses: actions/checkout@v4
    - name: Install Fern CLI
      run: npm install -g fern-api
    - name: Release Rust SDK
      env:
        FERN_TOKEN: ${{ secrets.FERN_TOKEN }}
        CRATES_IO_API_KEY: ${{ secrets.CRATES_IO_API_KEY }}
      run: |
        fern generate --target rust --version ${{ inputs.version }} --log-level debug

Regenerate and release your SDK

Navigate to the Actions tab, select the workflow you just created, specify a version number, and click Run workflow. This regenerates your SDK.

The rest of the release process depends on your chosen mode:

Release mode (default): If you didn’t specify a mode or set mode: release, no further action is required. Fern automatically tags the new release with your specified version number and initiates the publishing workflow in your SDK repository.
Pull request or push mode: If you set mode: pull-request or mode: push, Fern creates a pull request or pushes to a branch respectively. Review and merge the PR (pull-request) or branch (push), then tag a new release to initiate the publishing workflow in your SDK repository.

Once the workflow completes, you can view your new release by logging into crates.io, navigating to Dashboard, and looking under My Crates.

Release via CLI and environment variables

Set crates.io environment variable

Set the CRATES_IO_API_KEY environment variable on your local machine:

export CRATES_IO_API_KEY=your-actual-rust-token

Regenerate and release your SDK

Regenerate your SDK, specifying the version:

fern generate --target rust --version <version>

The rest of the release process depends on your chosen mode:

Release mode (default): If you didn’t specify a mode or set mode: release, no further action is required. Fern automatically tags the new release with your specified version number and initiates the publishing workflow in your SDK repository.
Pull request or push mode: If you set mode: pull-request or mode: push, Fern creates a pull request or pushes to a branch respectively. Review and merge the PR (pull-request) or branch (push), then tag a new release to initiate the publishing workflow in your SDK repository.

Once the workflow completes, you can view your new release by logging into crates.io, navigating to Dashboard, and looking under My Crates.

Configure sdk-config.yml

Add a unique crate name

Configure the client name

Configure GitHub delivery and crates.io publishing

Set up crates.io publishing authentication

Log into crates.io

Navigate to Account settings

Create a new API token

Configure crates.io authentication token

Publish your SDK

Release via a GitHub workflow (recommended)

Set up authentication

Add secret for your crates.io token

Add secret for your Fern API key

Set up a new workflow

Regenerate and release your SDK

Release via CLI and environment variables

Set crates.io environment variable

Regenerate and release your SDK

Configure `sdk-config.yml`