Abstract Background Evidence-based parenting programmes have strong evidence in preventing and mitigating violence, but in-person programmes are challenging to deliver at scale. ParentApp is an open-source, offline-first app-based adaptation of the Parenting for Lifelong Health for Parents and Teens programme to promote playful and positive parenting, reduce risks for sexual violence victimisation, and prevent violence against adolescents. This study aims to evaluate the effectiveness and cost-effectiveness of ParentApp compared to an attention-control group. Methods This study is a two-arm pragmatic cluster-randomised controlled trial to test whether ParentApp reduces adolescent physical abuse, emotional abuse, and sexual violence risks and victimisation at 1 month and 12 months post-intervention. Caregivers of adolescents aged 10–17 years and their adolescent children (N = 2400 caregiver-adolescent dyads) will be recruited in urban and peri-urban communities in the Mwanza region of Tanzania. A total of 80 study clusters will be stratified and randomised (1:1) to the intervention group, who will receive ParentApp with support through a WhatsApp group, or to an attention-control group, who will receive a water, sanitation, and hygiene app. Quantitative data will be collected through outcomes questionnaires with caregivers and adolescents, administered at baseline, 4 months post-baseline, and 16 months post-baseline, as well as through routine implementation data and ParentApp engagement data. Qualitative data will be collected through individual interviews and focus groups with caregivers, adolescents, and implementing partner staff. Discussion App-based interventions have the potential to expand access to evidence-based parenting support, but currently lack rigorous evidence in low- and middle-income countries. This is the first known randomised control trial of a hybrid digital parenting programme to prevent the abuse of adolescents in low- and middle-income settings. Trial registration The trial was registered on the Open Science Framework on 14 March 2023, registration: OSF.IO/T9FXZ .
