Despite growing use of 3D city models (3DCMs) and urban digital twins (UDTs), web tools for their processing and visualization remain scarce. We present an interoperable, high-performance web application composed of a 3D tiler and a WebGPU viewer that enables scalable conversion, streaming, and rendering of urban datasets in compliance with open standards. The proposed system allows users to explore large-scale 3DCMs interactively without local installations. A showcase visualizing quality-validation results for a 3DCM demonstrates practical value. Experiments confirm that 3D Tiles 1.1 standard enables scalable data management and richer interaction, whereas WebGPU offers up to 7x better rendering performance on modern hardware. By presenting this solution and usage example, we aim to foster development of next-generation web-based 3D geospatial, digital-twin, and metaverse solutions.