The key issue of this current study is related to shaping the attractiveness of heritage destinations, highlighting the significance of reuse and upgrading their historical buildings to achieve a high level of competitiveness and distinctiveness through a smart approach. Some of these cultural assets and events tend to be monotonous, and not so attractive for various categories of tourists, which negatively affects investment opportunities, tourism development, and social and economic resources. Furthermore, previous works have criticized the lack of evidence to support that the structure contains critical attributes and measurement items linked to the competitiveness of smart heritage destinations. As a result, this study aims to design and develop a composite index for evaluating these destinations and their buildings, which includes nine dimensions (attributes) and a set of key performance indicators (KPIs) of intelligent performance and competitiveness, reflecting the combination and noticing the distinct perspective between them. A mixed-methods approach was used between qualitative and quantitative methods to perform content validation on the proposed index. Furthermore, a pilot study was implemented for tourism heritage destinations to improve the quality and efficiency of the proposed index. Then, exploratory factor analysis (EFA) was used to analyze the data to develop the proposed index and measure its validity and reliability. Finally, the proposed composite index was finalized with 139 KPIs and applied to a case study (Salah El-Din Citadel). After that, we validated its utility in providing a quantitative evaluation of this heritage destination, identifying critical intervention priorities, and determining dimensions that need to be restructured. Additionally, it highlighted recommendations for future improvements to strengthen these heritage destinations to become smart heritage destinations capable of competition in the tourism sector.