Abstract Issue Informal carers provide an important and often overlooked role in the care of people with a cancer diagnosis. Our study sought to better understand carers needs and develop an online resource to help address the needs identified. There are not currently any widespread or embedded support services for cancer carers in Vietnam. Description of the Problem We conducted in-depth interviews and focus groups with both carers (n = 20) and healthcare providers (n = 22) to understand the needs and challenges of caring for someone with a cancer diagnosis. We discussed what resources would alleviate challenges and used these discussions to inform a process of co-designing an online resource. This process was modelled off a peer-led online resource intervention developed in the United Kingdom. This process of co-design is transferable to other contexts, and when adapted could help meet the needs of cancer carers in other lower and middle income countries. Results Carers in Vietnam reported (i) economic challenges of care; (ii) not being able to access facilities and secure accommodation when caring for inpatients; (iii) lack of information about cancer and nutrition; (iv) lacking emotional support; and (v) requiring training to support both the treatment and recovery of people under their care. Suggestions for content of an online resource included the need for contextually appropriate Vietnamese content, specific information on diet and nutrition, support in making decisions around treatment, and signposting for other services. Lessons Successful co-design of resources requires input from multiple key stakeholders. This is necessary to successful adapt and modify interventions for new contexts. Our process revealed new information about the roles and needs of carers, and enabled us to incorporate solutions to these needs within our online resource. Given the lack of other supportive services for carers, the development of such resources should be considered a priority. Key messages Cancer carers in Vietnam experience specific challenges including provision of nutrition, supporting navigation of hospital administration, and taking a central role in treatment decision-making. Co-designed online resources have the potential to support carers in providing relevant and appropriate information and signposting to other important services.