ClimApp is a mobile tool that translates climate service into personalized adaptation strategies to cope with thermal stress including heat and cold stress. ClimApp integrates weather forecast data with human heat balance models, to predict thermal strain experienced by humans. The app works globally in both hot and cold climates, in a temperature range from -50 C to +50 C. The App provides personalized health risk warning and advice for individuals, groups, organizations, public and private sectors, to support decision-making for adaptation strategies, and to improve the quality of life and health when facing thermal climate challenges. Targeted users: Initial targeted users are outdoor workers, occupational health and safety professionals, caregivers for elderly people and children who are more vulnerable to extreme heat and cold. It can also be used by other sectors/activities such as outdoor and leisure activities, and by the general population.