Extensions overview (OpenAPI) | 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 a separate file or by embedding them directly in your OpenAPI specification. See Overlays 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-basic`	Customize basic authentication parameter names and environment variables
`x-fern-bearer`	Customize bearer authentication parameter names and environment variables
`x-fern-availability`	Mark availability status (beta, generally-available, deprecated)
`x-fern-base-path`	Set base path prepended to all endpoints
`x-displayName`	Specify how tag names display in your API Reference
`x-fern-enum`	Add descriptions and custom names to enum values
`x-fern-examples`	Associate request and response examples
`x-fern-explorer`	Control API Explorer (playground) availability globally or per endpoint
`x-fern-global-headers`	Configure headers used across all endpoints
`x-fern-header`	Customize API key header authentication parameter names and environment variables
`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-sdk-variables`	Set common path parameters across all requests
`x-fern-parameter-name`	Customize parameter variable names
`x-fern-property-name`	Customize object property variable names
`x-fern-retries`	Configure retry behavior for endpoints
`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.