Default values

The x-fern-default extension lets you specify a client-side default value for a path, header, or query parameter, including headers defined under x-fern-global-headers. When present, the generated SDK makes the parameter optional and automatically sends the default value if the caller omits it. x-fern-default supports string and boolean values; other types (such as numbers) are ignored.

This is useful for pinning an API version header or a region path parameter while still allowing callers to override the value.

Path parameters

In the example below, the SDK sends us-east-1 for region when the caller doesn’t specify one.

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paths:
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  /regions/{region}/resources:
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    get:
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      operationId: list_resources
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      parameters:
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        - name: region
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          in: path
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          required: true
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          x-fern-default: "us-east-1"
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          schema:
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            type: string

Headers

In the example below, the SDK sends 2024-02-08 for X-API-Version when the caller doesn’t specify one.

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paths:
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  /users:
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    get:
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      operationId: list_users
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      parameters:
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        - name: X-API-Version
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          in: header
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          x-fern-default: "2024-02-08"
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          schema:
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            type: string

Query parameters

In the example below, the SDK sends false for verbose when the caller doesn’t specify one.

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paths:
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  /search:
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    get:
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      operationId: search
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      parameters:
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        - name: verbose
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          in: query
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          x-fern-default: false
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          schema:
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            type: boolean

Global headers

In the example below, the SDK sends 2024-02-08 for the X-API-Version global header when the caller doesn’t specify one.

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x-fern-global-headers:
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  - header: X-API-Version
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    name: version
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    x-fern-default: "2024-02-08"