Cooperative social responsibility emerges as a comprehensive approach that encompasses economic, social, environmental, ethical, technological, and governance aspects. It essentially advocates for sustainability in organizations in the popular and solidarity financial sector. This research project aimed to design and test the validity of an instrument to measure compliance with these principles in savings and credit cooperatives in Ecuador, specifically focusing on the first segment. To this end, a tool was created, divided into six theoretical areas and 33 questions, based on classic models of social responsibility and international standards such as ISO 26000 and GRI, and linking them to the relationship between cooperative principles and the Sustainable Development Goals. The methodological strategy applied was quantitative, correlational, and non-experimental. The survey included 2,216 employees and managers from 19 Ecuadorian cooperatives, which allowed for the use of various statistical techniques to support the instrument’s validity. For example, an exploratory factor analysis (EFA) was performed, in which the sampling adequacy index (SAI) reached 0.980 and Bartlett’s test of sphericity showed significance (p < 0.000). Internal reliability (Cronbach’s α overall = 0.971), composite reliability (CR > 0.78), and convergent validity (in a suitable range) were also evaluated. The questionnaire’s structure clearly confirmed the validity of the theoretical model, without revealing any concerning cross-loadings and demonstrating high consistency between the different items. The findings indicate, in most cases, that the instrument is reliable and valid for assessing the construct in cooperatives from the first segment.