TypeScript serde layer

Fern’s TypeScript SDK generator includes an optional serde layer that determines whether the generated SDK matches your original API naming conventions (snake_case vs. camelCase, case-sensitive fields) or follows TypeScript conventions. This serde layer is controlled by the serdeLayer option in the TypeScript target’s generation block in sdk-config.yml.

By default, the serde layer is disabled, meaning field names are preserved exactly as they appear in your API specification.

When to enable the serde layer

targets:
  - language: typescript
    generation:
      serdeLayer: true # Enable serde layer

When you turn on the serde layer (serdeLayer: true), the TypeScript SDK generator includes custom serialization code that:

• Transforms all property names from your API to camelCase
• Validates requests and responses at runtime
• Supports complex types like Date and Set.

Enable the serde layer when you want idiomatic TypeScript conventions and don’t have case-sensitive field conflicts. Keep it disabled when your API has fields that differ only by casing or when you need exact field name preservation.

Additional configuration options

Set useBigInt: true alongside an enabled serde layer to preserve precision for large numbers. It only takes effect when the serde layer is enabled (serdeLayer: true), as it requires the custom serialization infrastructure.

sdk-config.yml doesn’t have the skipResponseValidation and allowExtraFields options yet. To use them with generators.yml, see the Legacy TypeScript serde layer page.

targets:
  - language: typescript
    generation:
      serdeLayer: true # Enable serde layer
      useBigInt: true  # Preserve precision for large numbers

For the complete list of all TypeScript configuration options, go to TypeScript configuration.