Research on negative partisanship and affective polarization shows that wholesale rejections of individual parties are a common and growing phenomenon. This article offers a novel perspective on assessments of parties by considering citizens' legitimacy perceptions of political parties as institutional players. Combining research on political parties and public opinion, I develop a theoretical framework that explains how parties' characteristics shape their perception as legitimate institutional players. I argue that governing experience, age, ideology, and democratic behaviour provide informational cues to citizens about how democratically dangerous a party is. To test my argument, I fielded a cross-sectional survey in seven West European countries and a large-scale survey experiment. The results consistently show that citizens use party-level cues such as ideological moderation and democratic behaviour to form party legitimacy perceptions. The findings have important public opinion implications for political parties and their institutional role in democracies.