The paper presents the methodological premises of an ergonomic diagnostic tool which assesses the utility as well as functionality of a particular internet platform. This assessment is supposed to enable the improved functioning of the system which involves, on the one hand, the platform users, and on the other hand, some internet application technologies. The proposed method has a qualitative-heuristic character and involves seven assessment criteria. The authors suggest using one of the two detailed alternatives (based on a check-list) of assessment: point estimation of the mean or application of fuzzy logic for determining group and comprehensive evaluations.