In digital environments, the activity of a knowledge worker is in part dedicated to the developments of their instruments, ie. the configurations of tools, the setting up of information structures, and the development of computer-related skills. Users are not assisted in this constructive dimension of their activities, where a certain complexity exists due to the levels of sophistication and the instability of digital environments. We propose a theoretical model of digital instrument in order to understand, and to detect from a user's traces of interaction, the apparition and the development of digital instruments. From this capacity to detect digital instruments, our goal is to provide users with a reflexive assistance related to the constructive dimension of their work.