During a global pandemic, how can we best prompt social media users to demonstrate discernment in sharing information online? We ran a contextual adaptive experiment on Facebook Messenger with users in Kenya and Nigeria and tested 40 combinations of interventions aimed at decreasing intentions to share misinformation while maintaining intentions to share factual posts related to COVID-19. We estimate precise null effects of showing users warning flags or suggesting related articles alongside misleading posts, tactics used by social media platforms. Instead, users share more discerningly when they are given tips for spotting misinformation or are nudged to consider information’s accuracy, reducing misinformation sharing by 7.5% and 4.5% relative to control, respectively. We find significant heterogeneity in response to these treatments across users, indicating tips and the accuracy nudge affect outcomes through separate mechanisms. These low-cost, scalable interventions have the potential to improve the quality of information circulating online.