The main objective of this article is to expose the process underlying the co-creation and in situ validation of a digital tool for self-regulation correction, and this, within the broader framework of a large-scale action research (Action concertée FRQSC-MÉQ 2020-2023 : projet MultiNumériC). This digital tool allows students, through the self-recording of their writing mistakes, to establish their own evolving portrait in real time—and mobile—of their strengths and difficulties in syntax, punctuation as well as lexical and grammatical spelling. The co-creation team (teacher-researcher and university researchers) observed, throughout the 2021-2022 school year, three groups of secondary 5 students who experimented and criticized the digital tool deployed, which enabled them to gradually improve its technological and didactic efficiency.