Design configuration interfaces to be flexible and extensible rather than overly specific. When creating configuration objects: 1. Make configuration parameters optional when possible with sensible defaults 2. Allow for arbitrary additional properties rather than creating specific fields for custom configurations **Example - Instead of this:** ```typescript export interface AxiosRequestConfig { // other properties... customConfig?: Record; } // Required configuration parameter getUri(config: AxiosRequestConfig): string; ``` **Do this:** ```typescript export interface AxiosRequestConfig { // other properties... [key: string]: any; // Allow arbitrary properties } // Optional configuration parameter getUri(config?: AxiosRequestConfig): string; ``` This approach allows consumers to extend configurations naturally without requiring interface changes for each new use case, while maintaining backward compatibility through sensible defaults.