Two Hungarian cities — Pécs (population 140,000) and Miskolc (population 155,000) — are jointly building the modelling, data, and governance infrastructure needed for energy transition. Rather than implementing a single intervention, the project creates the tools and institutional architecture that enable data-driven decision-making: digital monitoring systems for emissions and energy, feasibility studies for solar, microgrids, and energy storage, mobility surveys, circular economy assessments, and a Climate Neutrality Platform convening the 26 signatories of Pécs's Climate City Contract.