Overview of OpenAPI extensions | Fern Documentation

Fern supports a variety of OpenAPI extensions that enhance your API specification and generate higher-quality SDKs.

You can apply these extensions in two ways: by overlaying them in separate override files or by embedding them directly in your OpenAPI specification. See Overrides for more information.

Available extensions

The table below shows all available extensions and links to detailed documentation for each one.

Extension	Description
`x-fern-version`	Configure API version schemes and headers
`x-fern-audiences`	Filter endpoints, schemas, and properties by audience
`x-fern-availability`	Mark availability status (beta, generally-available, deprecated)
`x-fern-base-path`	Set base path prepended to all endpoints
`x-fern-enum`	Add descriptions and custom names to enum values
`x-fern-examples`	Associate request and response examples
`x-fern-global-headers`	Configure headers used across all endpoints
`x-fern-ignore`	Skip reading specific endpoints or schemas
`x-fern-sdk-method-name`	Customize SDK method names
`x-fern-sdk-group-name`	Organize methods into SDK groups
`x-fern-parameter-name`	Customize parameter variable names
`x-fern-property-name`	Customize object property variable names
`x-fern-type-name`	Override auto-generated names for inline schemas
`x-fern-server-name`	Name your servers

Request a new extension

If there’s an extension you want that doesn’t already exist, file an issue to start a discussion about it.

FastAPI

FastAPI allows you to add extensions directly in your route decorators and models. See our FastAPI integration guide for detailed examples.