Formal international law is stagnating in terms both of quantity and quality. It is increasingly superseded by ‘informal international lawmaking’ involving new actors, new processes, and new outputs, in fields ranging from finance and health to internet regulation and the environment. On many occasions, the traditional structures of formal lawmaking have become shackles. Drawing on a two-year research project involving over 40 scholars and 30 case studies, this article offers evidence in support of the stagnation hypothesis, evaluates the likely reasons for it in relation to a ‘turn to informality’, and weighs possible options in response. But informal structures can also become shackles and limit freedom. From practice, we deduce procedural meta-norms against which informal cooperation is increasingly checked (‘thick stakeholder consensus’). Intriguingly, this benchmark may be normatively superior (rather than inferior) to the validation requirements of traditional international law (‘thin state consent’).