This paper explains how the 193 first nationally determined contributions (NDCs) specify the vague criteria of differentiation of the Paris Agreement as subsequent practice (Article 31(3)(b) VCLT). Combining a legal analysis with an original, systematic empirical analysis of the NDCs, the paper provides transparency without judgment respecting the self-defined approach to differentiation of the Paris Agreement. Operationalising criteria of differentiation that are representatively recognised and affect subsequent practice are the term ‘fairness’, absolute emissions (most frequently specified by unconditional quantified absolute emissions targets or the respective share in global or regional emissions), and the emissions per capita (the most common parameter to define fairness). However, the open weight of these criteria compared to other, less uniformly recognised criteria of differentiation and the dominance of the individualistic term ‘fairness’ make clear that the criteria of differentiation are only slightly narrowed; the self-defined approach to differentiation still dominates. Based on the most recognised criteria of the NDCs, the paper suggests an open-ended reporting table to structure the criteria of differentiation, facilitate their comparison, and enhance their transparency.