This paper explores the integration of principles of antifragile planning in the systems of governance and assessment tools for supporting the management of World Heritage Sites. The paper argues, after describing the management and evaluation procedures used by UNESCO for monitoring the effectiveness of World Heritage, such as Enhancing our Heritage toolkit, that these procedures focus primarily on maintaining the Outstanding Universal Value of World Heritage properties, without considering the possible implications in respect of the wider social, economic, and environmental context. In this respect, the aim of the paper is to orient a more complete assessment tool that considers the relationship and the reciprocal impacts between property and wider setting. Hence, the paper presents the principles of antifragile planning as a framework of orientations that can contribute to World Heritage evaluation tools. Hence, the paper proposes an assessment tool which integrates existing assessment tools developed by UNESCO for evaluating the management of World Heritage Sites and principles of antifragility to orient the policy design. Finally, we discuss the case of the World Heritage Site City of Vicenza and Palladian Villas of the Veneto, which lets us use the proposed assessment tool during the process of updating of its management plan, in force at the time of writing. The tool shows, as results, that the different approaches integrated are complementary and that this integration is a possible way to achieve a wider assessment tool that can address the management policy design in terms of antifragility. This paper aims to contribute to the development of assessment tools which include the antifragile dimension to enhance a policy design for the management of World Heritage properties effective for the property and its surroundings.