BackgroundReducing the rates of sexually transmitted infections (STIs) among young people is a public health priority. The best way to avoid STIs from penetrative sex is to use a condom, but young people report inconsistent use. A missed opportunity to intervene to increase condom use is when young people access self-sampling kits for STIs through the internet. The potential of this opportunity is enhanced by the increasing numbers of young people being tested through this route every year in England. Hence, in a cocreation by young people, stakeholders, and researchers, Wrapped was developed––a fully automated, multicomponent, and interactive digital behavior change intervention developed for users of STI self-sampling websites, who are aged 16-24 years.ObjectiveThis paper is a protocol for a feasibility randomized controlled trial (fRCT). The fRCT seeks to establish whether it is feasible to run a randomized controlled trial to test the effectiveness and cost-effectiveness of Wrapped. Wrapped aims to reduce the incidence of STIs through increasing correct and consistent use of condoms among users of STI self-sampling websites, who are aged 16-24 years.MethodsA 2-arm parallel-group randomized fRCT of Wrapped plus usual care, compared to usual care only (basic information on STIs and condom use), with a nested qualitative study. A minimum of 230 participants (aged 16-24 years) are recruited from an existing chlamydia self-sampling website. Participants are randomized into 1 of 2 parallel groups (1:1 allocation). Primary outcomes are the percentage of users recruited to the fRCT and the percentage of randomized participants who return a chlamydia self-sampling kit at month 12. Additionally, besides chlamydia positivity based on biological samples, surveys at baseline, month 3, month 6, and month 12, are used to assess condom use attitude, behavioral capability, self-efficacy, and intention, along with details of any partnered sexual activity and condom use, and health economic data. Nested qualitative interviews with trial participants are used to gain insight into the factors affecting recruitment and attrition.ResultsRecruitment to the fRCT began in March 2021 and was completed in October 2021. Data collection was completed in December 2022.ConclusionsThis feasibility study will provide data to inform the design of a future-definitive trial. This work is timely given a rapid rise in the use of internet testing for STIs and the sustained high levels of STIs among young people.Trial RegistrationISRCTN Registry ISRCTN17478654; http://www.isrctn.com/ISRCTN17478654International Registered Report Identifier (IRRID)DERR1-10.2196/43645