The article questions the notion of a platform state that guided the coordinated reform activity of the French state, undertaken between 2014 and 2017, at the General Secretariat for Government Modernization. Based on an in-depth ethnographic study of the modernization services, it shows how the platform state took shape in an application for identifying and exchanging administrative data, called FranceConnect. From the choice of protocols to compliance with the law or the formulation of identity, the administrative and computer design of the application has undergone various technical, political and legal tests. We will see how, in these tests, two characteristics of the state in relation to information technologies were shaped: digital sovereignty, and the ergonomics of public services.