AIM: The aims of this paper are (1) to present the results of the development, content validation and implementation study of the Relationship Competencies Guiding Tool; (2) to provide examples of how each item in the tool is reflected in clinical narratives written by nurses and justify the corresponding scores after the evaluation; (3) to present how the language and content of the narratives are interpreted with the tool and to describe an exemplar; and (4) to present barriers to and facilitators of the application of the tool. BACKGROUND: From a person-centered care approach, the fostering of authentic relationships with patients is key to achieving therapeutic benefits. Therefore, it is essential to help nurses establish meaningful relationships with patients and help them acquire these abilities. Clinical narratives can be used as a way to promote reflective practice and professional competency development among nurses. A tool to evaluate the knowledge, skills, attitudes and values necessary for developing authentic encounters with patients through clinical narratives was developed, validated and implemented. DESIGN: An instrument-development study comprised of three steps: (1) conceptualization; (2) item generation and content validity; and (3) implementation of the tool and linguistic evaluation. METHODS: This study was conducted in three major steps. Step one entailed conceptualization. Step two included the generation of items and content validation. In step three, the tool was used to independently evaluate 25 narratives. One of these narratives was also linguistically analysed to provide a comprehensive view of the interpretative strategies deployed by evaluators. RESULTS: The Relationship Competencies Guiding Tool was developed, validated and implemented. It could help nurses work on nursing relationship-based professional competencies, guided the evaluators in the process of assigning scores to the corresponding items and helped the researchers identify certain barriers and facilitators before and during the narrative evaluation process. CONCLUSIONS: The tool has been shown to be clear, relevant and conceptually and linguistically suitable for evaluating clinical narratives. The Relationship Competencies Guiding Tool could be applied to interpret how nurses reflect professional competencies in a clinical narrative as a preliminary step in the construction of a measurement tool. TWEETABLE ABSTRACT: From a person-centered relationship-based care approach, clinical narratives can be used to promote professional competencies between nurses. The Relationship Competencies Guiding Tool may help evaluate the knowledge, skills, attitudes and values necessary for developing authentic encounters with persons/families, as reflected by nurses' clinical narratives.