Parameter Names | Fern Documentation

By default, Fern uses the property names from your AsyncAPI message schemas as SDK parameter names. You can customize these using the x-fern-parameter-name extension.

Customize message property names

Use x-fern-parameter-name to specify custom parameter names for message properties:

asyncapi.yml

1 components:
2   schemas:
3     UserEvent:
4       type: object
5       properties:
6         user_id:
7           type: string
8           description: Unique user identifier
9           x-fern-parameter-name: userId
10         created_at:
11           type: string
12           format: date-time
13           x-fern-parameter-name: createdAt
14         notification_type:
15           type: string
16           enum: [email, sms, push]
17           x-fern-parameter-name: notificationType

This generates SDK methods with cleaner parameter names:

1 // Instead of send({user_id: "123", created_at: new Date(), notification_type: "email"})
2 client.sendNotification({
3   userId: "123",
4   createdAt: new Date(),
5   notificationType: "email"
6 });

Language-specific parameter names

You can specify different parameter names for different programming languages:

asyncapi.yml

1 components:
2   schemas:
3     OrderEvent:
4       type: object
5       properties:
6         order_id:
7           type: string
8           x-fern-parameter-name:
9             python: order_id
10             typescript: orderId
11             go: OrderID
12             java: orderId
13             csharp: OrderId

Channel parameter names

Customize parameter names for channel address variables:

asyncapi.yml

1 channels:
2   user/{user_id}/notifications:
3     address: user/{user_id}/notifications
4     parameters:
5       user_id:
6         description: User identifier
7         x-fern-parameter-name: userId
8         schema:
9           type: string

This ensures consistent naming conventions across your SDK while maintaining compatibility with your existing message formats.