Fern allows you to import other APIs into your API.

This is often useful if:

  • you want to reuse another API’s types in your API
  • you want to combine multiple microservices’ APIs into one SDK (similar to the AWS SDK)

Registering the dependency API

The first step is to register the API you want to depend on. To do this, use the register compiler command:

$ fern register
[some-dependency]: Uploading definition...
[some-dependency]: Registered @fern/some-dependency:0.0.1

Depending on the registered API

To add a dependency on another API, you simply create a folder in your Fern Definition to “house” the dependency. Inside the folder, create a special file __package__.yml which specifies the dependency and version you want to add.

├─ fern.config.json
└─ api/ # your API
  ├─ generators.yml
  └─ definition/
    ├─ api.yml
    ├─ imdb.yml
    └─ my-folder
      └─ __package__.yml
  name: @fern/some-dependency
  version: 0.0.1

When you compile the API with fern generate, the __package__.yml file will effectively be replaced with the API you’re depending on.