How might we innovate digital tools for citizen engagement with visual methods to ‘retool’ citizen science and invite more people to document their lived experiences as inputs to urban planning and policy? And could we do so in a participatory process that uses principles of Data Feminism and Design Justice to diversify who has a seat at the table in the tool development, and whose interest are built into the tools we make? Forged in the fire of such burning questions, we present the UB App as an open-source photovoice application for smartphones, co-created during the Urban Belonging Project (2020-22) in a process that involved scholars from Copenhagen and Amsterdam, professional urban planners, citizen engagement experts, and seven marginalized communities in Copenhagen (deaf, lgbtq+, physically disabled, mentally vulnerable, houseless, internationals, and ethnic minorities). At the 2023 FOSDEM, we are excited introduce the UB App and the UB Toolkit, and use examples from our design process to discuss the potentials and challenges of involving a multitude of voices and perspectives in the development of digital citizen science tools. We touch upon; how inputs from different stakeholders shaped decisions about what data collection the app makes possible; how it mitigates issues of privacy and visual and spatial literacy to make the app as inclusive as possible; and how design criteria were translated into app features that open new empirical opportunities for community engagement.