An efficient and accurate calculation platform of building energy consumption and carbon emissions at the urban scale is a prerequisite for low-carbon oriented urban design or urban renewal. On this basis, Urban Energy & Carbon Cloud (UECC), a novel and efficient simulation platform, focuses on evaluating city-scale building energy use and carbon emissions is developed. UECC is developed in accordance with the Guidelines for Calculating Energy Consumption and Operational Carbon Emissions of Urban Buildings, the first of its kind in China. UECC provides a suite of features and application scenarios such as the low carbon urban planning and design for urban planners, the urban electric system planning and district energy system planning for city energy managers, the energy saving potentials of different building energy efficiency initiatives for energy consultants and policy-makers, etc.