This article examines the development of international human rights standards and oversight mechanisms directed at addressing the negative effects of imprisonment. We identify this as the rules-based prison-regulation project, widely endorsed by international organizations and legal scholars. However, with a focus on the United Nations Standard Minimum Rules for the Treatment of Prisoners, we argue that this project has inherent limitations, as it is based on (a) a reductive understanding of carceral harms and (b) a rule-centric ontology of prisons. By challenging these foundations, we explore whether the project exemplifies “cruel optimism” (Berlant, 2011), where the pursuit of improved prison regulation could inadvertently hinder societal flourishing. We argue that the continuous search for new and better prison standards may perpetuate rather than alleviate the problems associated with imprisonment unless accompanied by explicit strategies for countering prison growth and dramatically reducing prisoner numbers, for building the democratic power of prisoners and communities targeted by imprisonment, and continual linkages between prison conditions and the wider political-economic institution of imprisonment. We conclude that engaging with prisons as sites of relational power in practice must underlie any quest to reduce the harms of imprisonment.