Fern supports a variety of OpenAPI extensions that enhance your API specification and generate higher-quality SDKs and CLIs.
You can apply these extensions in two ways: by overlaying them in a separate file or by embedding them directly in your OpenAPI specification. See Overlays for more information.
The table below shows all available extensions and links to detailed documentation for each one.
If there’s an extension you want that doesn’t already exist, file an issue to start a discussion about it.
FastAPI allows you to add extensions directly in your route decorators and models. See our FastAPI integration guide for detailed examples.