The “attitude-behavior gap” in environmental sustainability is when individuals want to be eco-friendly, but their actions contradict that. To promote eco-friendly behavior among consumers, this study investigates a redesign of e-commerce platforms to bridge the attitude-behavior gap in online shopping. We introduce explanable environmental cues through SEER - Sustainable E-commerce with Environmental-impact Rating. A quasi-randomized case-control experiment with 98 subjects demonstrates the efficacy and user-friendliness of the proposed concept design. The case group using SEER showed significantly more eco-friendly behavior than the control group (p < 0.005) and reported that the components introduced in SEER made finding eco-friendly products more convenient, simultaneously increasing their trust in the labels because of the provided explanation. In addition, SEER has been rated highly in terms of usability, with a System Usability Scale (SUS) score of 79.18. [Read]