We describe a co-design approach to design the online WebSoKeyTo used to design AAC. This co-design was carried out between a team of therapists and a team of human-computer interaction researchers. Our approach begins with the use and evaluation of an existing SoKeyTo AAC design application. This step was essential in the awareness and definition of the needs by the therapists and in the understanding of the poor usability scores of SoKeyTo by the researchers. We then describe the various phases (focus group, brainstorming, prototyping) with the co-design choices retained. An evaluation of WebSoKeyTo is in progress.