I noticed your validation buttons didn’t seem to give the proper validation messages. You need to use an Output widget to capture the output you wish to display (see Widget Events — Jupyter Widgets 8.1.1 documentation). Actually, it does seem like at least one part of the code in outils.py does use an output widget to properly capture output messages in a button on_click handler (in class Question, for example, the output is displayed inside of a with self.out context handler), but other places do not capture the output messages in an output widget (for example, in Question_ouverte, the button on_click handler displays output without redirecting it to an output widget). I would suggest making the Question_ouverte class on_click handler behave like the Question on_click handler, i.e., display an output widget in the widget layout, and use it to capture the markdown displayed in the on_click handler.