Control Property Naming and Casing

TypeScript SDKs support configurable property naming to match your API’s field naming conventions. You can either normalize property names to a consistent casing style, or preserve the exact names from your OpenAPI spec.

Property Casing

Use modelPropertyCasing to control whether generated TypeScript types use camelCase or snake_case property names.

Configuration

<sdk-root>/.speakeasy/gen.yaml


typescript:
  modelPropertyCasing: "camel" # or "snake"

Options

camel (default): Properties use camelCase naming (e.g., firstName, createdAt)
snake: Properties use snake_case naming (e.g., first_name, created_at)

Examples

camelCase naming (default)


// Configuration: modelPropertyCasing: "camel"
export type User = {
    id: string;
    firstName: string;
    lastName: string;
    emailAddress: string;
    createdAt: Date;
    isActive: boolean;
};

snake_case naming


// Configuration: modelPropertyCasing: "snake"
export type User = {
    id: string;
    first_name: string;
    last_name: string;
    email_address: string;
    created_at: Date;
    is_active: boolean;
};

Preserve Original Property Names

Use preserveModelFieldNames to keep the exact property names from your OpenAPI spec without any normalization. This is useful when:

Your API uses unconventional naming (e.g., properties starting with _)
You need exact parity with existing SDKs or API documentation
Your property names have special meaning that would be lost through normalization

Configuration

<sdk-root>/.speakeasy/gen.yaml


typescript:
  preserveModelFieldNames: true

Interaction with modelPropertyCasing

When preserveModelFieldNames is enabled, modelPropertyCasing only affects synthetic fields generated by Speakeasy (like additionalProperties, clientID, etc.). Properties defined in your OpenAPI spec will use their original names exactly as specified.

Example

Given an OpenAPI spec with these properties:


components:
  schemas:
    Event:
      type: object
      properties:
        _raw:
          type: string
        __metadata:
          type: object
        event_type:
          type: string
        EventID:
          type: string

Without preservation (default):


// preserveModelFieldNames: false (default)
// Properties are normalized based on modelPropertyCasing
export type Event = {
    raw: string;        // Leading underscores removed
    metadata: object;   // Leading underscores removed
    eventType: string;  // Converted to camelCase
    eventId: string;    // Converted to camelCase
};

With preservation:


// preserveModelFieldNames: true
// Properties match OpenAPI spec exactly
export type Event = {
    _raw: string;       // Preserved with underscore
    __metadata: object; // Preserved with underscores
    event_type: string; // Preserved as snake_case
    EventID: string;    // Preserved as PascalCase
};

When to Use

Scenario	Recommendation
Standard APIs with conventional naming	Use `modelPropertyCasing` (default)
APIs with leading underscores (e.g., `_raw`, `_links`)	Use `preserveModelFieldNames: true`
Migrating from existing SDK with specific field names	Use `preserveModelFieldNames: true`
Mixed naming conventions that must be preserved	Use `preserveModelFieldNames: true`

Last updated on January 22, 2026