This paper critically examines efforts to make the UN Al-Qaida and ISIL sanctions list interoperable with the Advanced Passenger Information (API) data used by the global aviation industry. The aim of this experiment to control the movements of foreign terrorist fighters. It is part of a panoply of recent UN Security Council (UNSC) measures requiring states to enhance information sharing about poten-tial terrorist threats. Drawing on interviews with UNSC experts and other IOs, I show how this technical project of list implementation has far-reaching political and legal effects. I argue that interoperability is forging powerful new forms of global security governance and stretching the boundaries of collective security. Empirically analysing the mundane politics of data formatting is important because it reveals how governance technologies (such as databases) actively participate in the creation of new forms of global security law, in the shadows of where we usually think the law to be.