ObjectiveTo develop a rapid screening tool for the identification of frailty in medical calls and other out-of-hospital acute care services.DesignDevelopment study based on cross-sectional data. A set of potential items were developed based on existing frailty tools and other relevant literature by a panel with geriatric and primary care expertise. The items and the Clinical Frailty Scale (CFS) were administered on a convenience sample of older urgent care patients. Further development of the tool was based on statistical analyses of this data material and final discussions in the panel.SettingUrgent care centre in Norway, data collected between January and August 2022.ParticipantsAll patients ≥70 years were eligible for inclusion, with the exception of patients triaged to the highest urgency level and patients not able to answer questions with no next of kin present.Primary outcomePotential items associated with frailty by CFS, measured by explained variance (adjusted R2values from linear regression analyses).ResultsNine potential items were developed and administered on 200 patients (59% female), of whom 48% were 70–79 years, 38% were 80–89 years and 14% were ≥90 years. The median CFS score was 4 (living with very mild frailty). Receiving help weekly, being homebound and using a walking aid were identified as strong indicators of frailty (adjusted R2values 59%, 48% and 43%, respectively). Together these three factors could explain 74% of the variation in CFS scores.ConclusionsReceiving help weekly, being homebound and using a walking aid are strong indicators of frailty among urgent care patients. We developed a frailty screening tool for medical calls—FastFrail—consisting of three simple, binary questions (yes/no) on these aspects. We hypothesise that FastFrail can supplement traditional symptom-based triage and enable more accurate assessment of older adults calling for acute medical help. We intend to test the tool in clinical practice.