Additional properties

When OpenAPI schemas use the additionalProperties keyword, Speakeasy generates SDKs that handle these flexible object types automatically.

Using additionalProperties in SDKs

Important: additionalProperties is an internal implementation detail. Pass objects with all properties directly - the SDK handles serialization and validation automatically.

The Speakeasy approach

Speakeasy sets additionalProperties to false by default unless explicitly defined otherwise. This encourages fully-typed objects with clear documentation. Most developers prefer closed objects by default, but setting additionalProperties: false in every schema would be tedious. Most backend frameworks that generate OpenAPI schemas don’t add additionalProperties: false, even when that’s the intended behavior.

Using additionalProperties: true

Set additionalProperties: true to accept arbitrary fields beyond the defined properties. This is useful for accepting unpredictable fields or allowing future extensions without schema updates.

Generated type structure

Usage

Using typed additionalProperties

Constrain additional properties to a specific type:

Generated type structure

Usage