This research explores the role and challenges of openness between digital healthcare platforms through the use of boundary resources in the Dutch healthcare system, focusing on factors influencing openness decisions. Traditionally, boundary resources facilitate arm’s-length relationships between platforms and their periphery. This study examines their specific contribution to platform-to-platform openness in digital healthcare. To properly define openness between platforms, a distinction was made between interoperability and platform-to-platform openness: interoperability focuses on the compatibility of platform resources, while openness emphasizes the provision or accessibility of these resources. Boundary resources are further divided into technical and social aspects, shaped by laws and regulations. A document analysis of key policy documents maps how these relevant boundary resources function. The importance of APIs is emphasized as a means to progress toward an interconnected digital healthcare system, however, the practical implications and impact of openness decisions leading to the formulation of API’s, particularly between platforms, remain somewhat unclear. Interviews with the most relevant stakeholders in the field provide further insight into the drivers and barriers affecting boundary resources adoption. Most emphasis is placed data exchange and transactional based platforms by the stakeholders. The distinction between interoperability and platform-to-platform openness in healthcare can help avoid conflating compatibility requirements with broader governance and strategic considerations, enabling more focused discussions on factors essential for platform-to-platform openness. Boundary resources, while holding significant potential to facilitate openness, are not clearly distinguished by platform owners in their application for inter-platform openness compared to openness toward complementors, while these two forms of openness can serve a distinct purpose. Openness concerns are further composed of involved technical costs, security and data liability issues, as well as competitive pressures, with the potential loss of operating models and market position adding additional complexity to these openness decisions. Regulatory direction stimulates the development of boundary resources to promote inter-platform openness by embedding platform connections within the broader market ecosystem. Boundary resources could be further utilized further to enable platforms to xtend their periphery and for addressing deeper infrastructural and collaborative challenges within the healthcare sector. Platform-to-platform openness is influenced not only by decisions of the platform owners themselves, but also by broader market dynamics, regulatory frameworks, and the platform environment. This research highlights the potential of boundary resources in tackling infrastructure, innovation, and data-sharing challenges in healthcare.