More and more people are living in the city areas which brings a huge demand for city services. Our cities are now equipped with all kinds sensors and the rise of Internet of Things (IoT) offers the opportunity to connect them together. Cities cannot become smart without the engagement of application developers and citizens. Efforts have been put on making data accessible to public. Past studies focused on the development of data management platforms to integrate data. This paper proposes a novel idea of integrating APIs instead data which not only improves the accessibility of data but also the efficiency. In this paper, a smart city architecture with API management platform is present on the basis of the +CityxChange project in Trondheim, as well as a demonstration of the API management platform to show how it works.