Generate REST API Reference | Fern Documentation

Fern generates REST API Reference documentation from an OpenAPI specification or Fern Definition. Once the API definition is set up, adding it to the docs takes just one line of configuration.

Fern also supports gRPC, GraphQL, WebSocket (AsyncAPI or Fern Definition), OpenRPC, and Webhook references.

Configuration

Set up your project structure

For OpenAPI/AsyncAPI: Add your specification file to your /fern directory and create a generators.yml that references it in the api.specs section

For Fern Definition: Add a definition/ directory with your API definition files (Fern auto-detects this)

generators.yml

1 api:
2   specs:
3     - openapi: "./openapi.yml"

Customize the layout

For a full list of configuration options and layout customizations, see Customize API Reference layout.

Include more than one API Reference

To include multiple, distinct API definitions in your documentation, use the api-name property. The api-name corresponds to the folder name containing your API definition.

This works with any combination of OpenAPI and Fern Definition formats. For example:

fern

fern.config.json

docs.yml

plant-api

openapi.yml# OpenAPI spec

generators.yml# References the OpenAPI spec

garden-api

definition

api.yml

Flat layout

Tabbed layout

For a simple setup without tabs, you can include multiple API References directly in your navigation: