The ‘EU arm’s length principle’ gradually evolved into an ‘EU arm’s length tool’ in the Starbucks, Fiat, Apple, and Amazon judgments of the General Court of the European Union (‘GC’). This contribution analyzes in detail why a ‘principle’ progressed into a ‘tool’ in these judgments. For this matter, it considers the arm’s length standard from the point of view of the regulation strategy of states (i.e., a reflexive regulation strategy) to govern the taxation of multinational companies. The author maintains that the regulatory design of the arm’s length standard entails a choice for ‘reflexive transfer pricing law’ and subsequently relies on that perspective for analyzing the judgments of the GC. This angle meticulously illustrates that the abuse of discretionary powers by the tax authorities in the process of monitoring the residual profit allocation of the taxpayer constitutes the relevant state aid problem. The contribution concludes that the GC eventually devised a rather toothless ‘tool’ that does not properly address this issue. At the same time, it also concludes that it should be relatively straightforward for the Court of Justice EU to finetune the ‘EU arm’s length tool’ in order to establish an effective and foreseeable reconciliation of EU state aid law and transfer pricing law. For this matter, the contribution puts forward a concrete recommendation.