Ensure API type definitions accurately reflect current implementations. When maintaining TypeScript definitions for APIs, regularly audit them against the actual source code to prevent developers from using non-existent or deprecated features. For API type definitions: 1. Remove outdated type declarations that no longer exist in the implementation 2. Add clear comments for deprecated features or known limitations 3. Document version changes that affect API types Example: ```typescript // INCORRECT: Keeping outdated type definitions /** * This function no longer exists in Express 5.0+ */ export function query(options: qs.IParseOptions): Handler; // CORRECT: Properly documenting API changes /** * @deprecated Removed in Express 5.0 (2014-11-06) * @see https://github.com/expressjs/express/blob/master/History.md#500-alpha1--2014-11-06 */ // export function query(options: qs.IParseOptions): Handler; ``` Accurate type definitions prevent confusion, reduce runtime errors, and improve developer experience when working with your API.