I design and build RESTful APIs that other developers actually enjoy integrating with — consistent resource naming, sensible status codes, and documentation that stays in sync with the code, usually via Postman collections or OpenAPI/Swagger.
This also covers third-party API integrations for systems you already rely on, webhook systems and event broadcasting for real-time updates, and the operational side — rate limiting, caching, and authentication — so the API holds up under real usage.