School counseling is a decision-making process in which high school students have to decide what higher education course they will register for. Many digital devices support high school students in this guidance process. Given the diversity of architectures and services offered by existing devices, the main goal of this project is to predict their impact on high school students. It is necessary, therefore, to propose a formal characterization of digital devices for school counseling. This paper proposes an ontology to represent knowledge of digital guidance devices. An instantiation of the ontology is performed for each device to be studied. The ontology is built to be able to identify the different functions of the digital devices, their types, and the relationships between the tools of the digital devices and the guidance actors. The ontology includes the tools that the user may use, the topics covered by the device, the elementary components, and the support used (mobile application, computer application, or website).