Whereas research has investigated links between personality and commenting behavior on various online platforms, research testing who comments positively, neutrally, or negatively in online scientific studies is missing. Herein, we tackle this gap, considering the HEXACO personality dimensions. Relying on a COVID-19 survey (N = 8,809), we find that, as compared to their counterparts, people high in Openness to Experience comment more; that people high in Extraversion and Openness to Experience commend more; and that those high in Emotionality write both more neutral comments and fewer complaints. Notably, these relations all appear to be modest. Combined, our findings provide novel insights into the relations between personality and commenting behavior in online scientific studies, suggesting that—while people with certain personality characteristics comment more in specific ways than others—researchers need not to worry too much that the comments they receive are overly biased.