Background Inadequate knowledge and skills and a lack of confidence to provide care have been identified as major unmet needs for carers of people with brain cancer. An online intervention was developed to address the unmet needs of carers of people with high-grade glioma. Methods Ten carers evaluated the intervention through multiple methods. Acceptability and usability were measured through online data analytics (unique page views, time on page), surveys, and interviews. Questionnaires measured potential impacts on distress (Distress Thermometer), depression, anxiety (Hospital Anxiety and Depression Scale), carer competence (Carer Competence Scale), carer preparedness (Caregiving Preparedness Scale), unmet needs (Supportive Care Needs Scale - Brain Tumor Specific for carers), usability and acceptability (USE). Results Results suggested the intervention had high levels of usability (usability scales' means range = 5.1 to 6.7 out of 7) and acceptability (M = 76.3/100). Correlations indicated the potential to impact depression. Qualitative findings highlighted benefits of the intervention as a comprehensive reliable resource that could validate and normalize carer experiences. Interview findings guided further improvements (eg, additional carer videos, content organization). Conclusions The study indicated high acceptability and usability of an online intervention for carers of people with high-grade glioma. This exploratory study also provided preliminary indications of a potential to decrease depression. However, a more robust, potentially longitudinal, investigation is needed with a larger and broader sample. Informed by this study, the intervention has been amended and a randomized controlled trial will further evaluate the enhanced intervention.