Climate-4-CAST contributes to climate neutrality by empowering local public authorities who struggle to integrate climate concerns into urban governance processes with limited municipal funding. High levels of uncertainty about emissions impacts, timing and cost of impacts, and potential of feedback effects are a barrier to climate action. Decision-makers are not climate subject experts: they speak a different language. Climate specialists need to translate their analyses in terms that municipal budget-makers understand; the decision-makers need a reliable science-based foundation on which to base their financial allocations and to monitor results. To tackle these problems, Climate-4-CAST equips local public administrations with an open source decision support tool to allow both a visualisation of individual measures’ emissions impacts in different scenarios and a cost-benefit analysis of the measures’ performance against city goals. Through transnational co-development and piloting, the tool will be adapted to local contexts and needs while allowing better cross-border coordination, e.g. on data. The operationalisation will be proof-tested with key decision-makers to ensure usability as a governance instrument for climate budgeting. Thus, the project accelerates cities' climate actions and improves policy implementation for climate neutrality. Swifter progress towards climate goals supports overall sustainable development in the BSR and also benefits citizens and businesses.