The Japan-India Nuclear Cooperation Agreement of 2016 is accompanied by a “Note on Views and Understanding” reflecting the conflict of views between the two States during the six and a half years of negotiation regarding the possibility of Indian nuclear testing and its impact on the bilateral nuclear cooperation. Japan asserted that if India were to conduct a nuclear test, it would cease cooperation and terminate the cooperation agreement, while the Indian side was of the view that it would not accept its current voluntary test moratorium being transformed into a legally binding obligation. This difference of opinion resulted in the accompanying Note. After its signing, however, the two sides apparently hold different views on the legal nature of the Note. This article examines the question of how the legal nature of an international instrument is to be determined in the light of the relevant ICJ jurisprudence among others.