This paper describes the development and reliability assessment of the Caring Nurse Observation tool (CNOT), which includes measures of verbal and non-verbal caring interactions. Using Watson caring and Watzlawick communication theories, observable indicators of caring were selected. After a content validity assessment, the 43 indicators of the tool were tested for inter-rater reliability using both role-playing and real-life nurse-patient interactions. Mean inter-rater agreement was 38% and 41%, respectively, in the two datasets, indicating reliability of the tool. the CNOT will aid nurses to document and demonstrate the impact of caring attitudes on health outcomes in research and clinical practice.