While urban design affects the public, most people do not have the time or expertise to participate in the process. Many online tools solicit public input, yet typically limit interaction to collecting complaints or early-stage ideas. This paper explores how to engage the public in more complex stages of urban design without requiring a significant time commitment. After observing workshops, we designed a system called CommunityCrit that offers micro-activities to engage communities in elaborating and evaluating urban design ideas. Through a four-week deployment, in partnership with a local planning group seeking to redesign a street intersection, CommunityCrit yielded 352 contributions (around 10 minutes per participant). The planning group reported that CommunityCrit provided insights on public perspectives and raised awareness for their project, but noted the importance of setting expectations for the process. People appreciated that the system provided a window into the planning process, empowered them to contribute, and supported diverse levels of skills and availability.