BACKGROUND: Young people face special challenges to accessing needed sexual and reproductive health (SRH) information and support. With high penetration and access, mobile phones provide a new channel for reaching young people, but there is little evidence around the impact of digital interventions on improving health outcomes. The Adolescent/Youth Reproductive Mobile Access and Delivery Initiative for Love and Life Outcomes (ARMADILLO) study will assess the effect of an intervention providing SRH information to young people via text message on their mobile phones in Kenya and Peru. This protocol details an open, individually-randomized, three-arm trial lasting seven weeks to assess the effect of the ARMADILLO intervention on dispelling myths and misconceptions related to contraception. A secondary objective is to determine whether youth given access to SRH information via text message can accurately retain that information. METHODS: Following a household enumeration, one eligible youth per household will be randomly selected for participation and randomized by computer into one of the three arms. Intervention arm participants will receive access to ARMADILLO content, control participants will receive no information, and 'Arm 3' participant interactions will vary by site: in Kenya, they will be alerted to various SRH domains and encouraged to learn on their own; in Peru, they will receive key content from each domain with the option to learn more if they wish. Participants will complete multiple-choice questionnaires administered by data collectors at baseline (prior to randomization), at intervention-period end (after week seven), and eight weeks after timing out of the intervention period. DISCUSSION: Part of the Sustainable Development Goal commitment towards ensuring healthy lives and promoting well-being for all at all ages includes a commitment to 'ensuring universal access to sexual health and reproductive health-care services, including for family planning, information and education'. If proven to be effective, interventions like ARMADILLO can bridge an important gap towards achieving universal access to SRH information and education for an otherwise difficult-to-reach group. TRIAL REGISTRATION: This trial was retrospectively registered with the ISRCTN Registry and assigned registration number ISRCTN85156148 on 29 May, 2018.