The article substantiates the theoretical and methodological principles of forming a methodological platform for diagnosing the economic activity of a trading enterprise as a basis for implementing a diagnostic process focused on the formation of special information used for making management decisions. It is noted that the diagnostics of economic activity of a trade enterprise as a component of management is a set of actions aimed at providing information support to management that requires from management staff systemic theoretical knowledge and applied skills of instrumental methods of identifying economic activity, trends, assessing causes of change, forecasting and the practical implementation of the identified opportunities to increase it, taking into account changes in the business environment and the needs of stakeholders. It is proved that the efficiency of diagnostics of economic activity is ensured by the appropriate methodology, which normalizes the organization of the diagnostic process, procedures and operations into a holistic system with clearly defined prerequisites, component composition and process of their implementation. The methodology framework is determined and the problem tree analysis of the formation of the methodological platform for diagnosing economic activity of trade enterprises is carried out. The architectural structure of the system of diagnosing economic activity of a trade enterprise through a combination of functional and support components, which are defining for productive functioning of the mechanism and efficiency of the diagnostic process, is considered. The sequence of stages of the diagnostic process and procedural aspects of verification of each of them is determined. It is proved that the efficiency of the process of diagnostics of economic activity is provided by an appropriate mechanism, which through a set of rules, special tools, methods and techniques launches and maintains a diagnostic study, thus ensuring the integrity of the diagnostic system. A conceptual model of the methodological platform for diagnosing economic activity of trade enterprises is developed, which integrates the identified preconditions and component composition of the methodology on the basis of systematicity and ensures the effectiveness of the process of obtaining information for management. The developed model allows to deepen and expand understanding of the essence of the system for diagnosing economic activity of the enterprise, its structure, regularities, the purposes and tasks of functioning, to provide high-quality instrumental support of the realization of diagnostic procedures and operations, to streamline the process of reception of the information for making management decisions focused on achieving target parameters of development of economic activity taking into account the dynamic changes in the business environment and consumer preferences.
