# How SDKs work

> Understand Fern's SDK generation process. Cloud-based workflow transforms API specifications into production-ready client libraries automatically.

Fern combines your API specifications with generator configurations and custom code to produce SDKs in multiple languages. By default, SDK generation runs on Fern's managed cloud infrastructure.

<Info>
  Alternatively, [you can run SDK generation on your own infrastructure](/sdks/deep-dives/self-hosted) to meet specific security or compliance requirements.
</Info>

## Generation workflow

Before generating SDKs, you'll configure your `fern/` folder with SDK generators specified in `generators.yml` and connect your API specification. You can also add custom code, tests, and other configuration as needed.

Running `fern generate` kicks off the cloud generation process and involves a few key steps:

<Steps>
  <Step title="Cloud execution">
    Fern allocates compute resources and pulls the appropriate Docker image for your specified generator version.
  </Step>

  <Step title="Generate core SDK">
    The Docker container executes the generation logic and produces your SDK's core files (models, client code, API methods).
  </Step>

  <Step title="Verify organization">
    Fern verifies your organization registration to ensure the complete SDK can be generated. Without organization verification, only partial SDK files (core code without package metadata) are produced.
  </Step>

  <Step title="Add package metadata">
    Fern completes the SDK by adding package distribution files such as `pyproject.toml`, `package.json`, README, and any dependencies.
  </Step>

  <Step title="Output to destination">
    Fern publishes or saves the complete SDK to your configured location (local filesystem, GitHub repository, package registry). After publication, developers can use your SDKs to integrate with your APIs.
  </Step>
</Steps>

<Accordion title="Architecture diagram" toc={true}>
  ```mermaid
  sequenceDiagram
      autonumber
      participant Dev as Developer
      participant Fern as Fern
      participant Docker as Docker Container
      participant Dest as Output Destination
      
      Dev->>Fern: fern generate
      Fern->>Fern: Allocate cloud compute
      Fern->>Docker: Pull & run generator image
      Docker->>Docker: Generate core SDK files
      Docker->>Fern: Return partial SDK
      Fern->>Fern: Verify organization
      Fern->>Fern: Add package metadata
      Fern->>Dest: Output complete SDK
  ```
</Accordion>