This article examines the principles of sustainable digital design as a holistic approach to web‐product development, wherein each interface optimization considers not only user experience and business metrics but also the material costs of computation, data transmission, and rendering. The relevance of this work is driven by the rapid increase in energy consumption of data centers and user devices under the influence of digitalization, and by the necessity to minimize the carbon footprint of web services amid constraints of the “green” energy system and social responsibility for product accessibility. It seeks to organize and measure important ways of eco-friendly web design—the choices of loading, dark styles, graphic types, shortening and shaking trees, client or server rendering options, adaptive delivery of content, and CO₂ budgets—based on their effects on speed, energy used by devices, and the environment. For this purpose, a careful look at industry reports, acade͏mic tests, and real-world studies was done, plus a metric comparison from the Web Almanac Core, Web Vitals, and lab tests. The novelty of this work lies in integrating ecological, economic, and technical metrics into a unified methodology. For each technique, comparable numerical estimates of carbon‐emission reduction and business‐efficiency gains are presented, and recommendations are developed for their combined application within the CO₂ budget of first‐screen delivery. Key findings indicate that activating lazy loading with a single HTML attribute can reduce transferred data volume and improve Time to Interactive by 20–30%; employing a dark theme on OLED displays under bright lighting can decrease display power consumption by up to 47%; and replacing PNG images with SVG sprites can reduce graphic payload by 60–80%. This article will be valuable to web designers, front‐end developers, product managers, and IT strategists seeking to marry high interface performance with a minimal
carbon footprint.