Information systems (IS) in Dutch first-line healthcare are organized complex and inefficiently. This limits innovation and interoperability of IS in this domain. Innovation is considered useful to make first-line healthcare more efficient. Digital platform literature shows a how a digital platform provides a more flexible approach to IS and greater rate of innovation. There is little ex-ante design knowledge on how to develop a digital platform. Also, transforming IS in healthcare is complex and often fails. Moreover, openness of a platform can enhance innovation but also introduces risks such as loss of control. This research focused on examining what architectural configurations can facilitate a desired level of platform openness for the Dutch primary healthcare domain. A design science research approach was used to answer this question. Design choices for architectural openness were distilled from literature. A concept artefact on design choices was developed and evaluated with domain experts. The study shows that openness is desired from the perspective of IS suppliers but that openness can never come at the cost of loss of quality or security. Respondents are reluctant to open up critical functionality embedded in the platform. Future researchers are suggested to study the design of boundary resources to manage control over complements and the relationship with complementors.