Thailand has numerous data sources related to smart city development; however, these data are often fragmented, focusing on specific systems, aspects, and technologies. This fragmentation poses challenges for inter-organizational use and collaborative development efforts. This research aims to develop a common data set for smart city development in Thailand, comprehensive characteristics of the seven key areas in smart city development: smart environment, smart mobility, smart energy, smart economy, smart people, smart living, and smart governance. The study employs a research and development methodology divided into three phases: (1) analyzing foundational data for smart city development from international and national organizations through a preliminary source, (2) investigating information and data management practices from key Thai organizations, and (3) synthesizing these findings to develop a common data set, designing a data dictionary for smart city in Thailand, and evaluating it with expert input. The results indicate significant advancements in city management and sustainability through the use of a standardized dataset. The data dictionary details the data domains, elements, and their properties, providing a valuable resource for expanding knowledge on common data sets for smart city. This tool will benefit Thailand’s administrators in managing smart city data and developing comprehensive databases. Additionally, it offers a foundation for scholars and researchers to further explore and develop fundamental data for smart city initiatives in other cities.