Background <p>Surrogate decision-makers (SDMs) of patients with serious illnesses (PSI) face significant challenges in making end-of-life decisions, including feeling unprepared and uncertain due to lack of clarity on what patients and they themselves value. We developed a digital SDM-focused intervention (<i>Careverse</i>) that provides educational materials and tools for SDMs to initiate and discuss values conversation with patients and clinicians. The aims of this study are (i) to test the impact of <i>Careverse</i> on SDMs self-reported engagement in care planning behaviours and (ii) to evaluate whether <i>Careverse</i> increases caregivers’ and patients’ self-reported satisfaction with care and improves patient outcomes.</p> Methods <p>This is a two-armed, parallel-design, single-blinded, participant-level randomised controlled trial of 100 identified decision-makers for patients with serious illness, along with their patients in a public university hospital in Singapore. Participants are English-speaking adult SDMs (21&#xa0;years and older) of PSIs, including brain tumours, spontaneous intracerebral haemorrhage, and late-stage chronic kidney disease. Physicians in charge must assess that the patient is an appropriate candidate for advance care planning (ACP). Eligible caregivers of these patients with serious illness are then assigned to the intervention or control group using randomisation stratified by patients’ conditions. We will assess SDM outcomes (engagement in care planning behaviours as a surrogate decision maker within 6 weeks—primary outcome; satisfaction with care; goals of care congruence, wellbeing) and patient outcomes (healthcare utilisation at end-of-life).</p> Discussion <p>This trial will provide much-needed empirical evidence about a SDM-focused digital care planning intervention to empower caregivers to engage more effectively in care planning behaviours and be better prepared for their SDM role. This trial will also test the effect of <i>Careverse</i> on improving both SDM’s- and patient-centred outcomes, and inform clinicians, payers and health systems seeking to adopt and scale effective and efficient digital strategies for supporting SDMs in real-world serious illness care settings.</p> Trial registration <p>ClinicalTrial.gov NCT07134881. Registered on 21 August 2025, <a href="https://clinicaltrials.gov/study/NCT07134881">https://clinicaltrials.gov/study/NCT07134881</a>.</p>