The high intensity of repetitive questions regarding product information, order status, and store policies in e-commerce businesses creates an additional workload for customer service and delays responses to customers. This research aims to implement a rule-based chatbot on the WhatsApp platform to automate customer service. The method used is the Waterfall software engineering model with stages of needs analysis, design, implementation, testing, and evaluation. The chatbot was implemented using Python integrated with WhatsApp Business API utilizing quick reply features. Functional testing results on 100 question samples show 87% accuracy. Usability testing using the System Usability Scale (SUS) on 30 users yielded a score of 78.5 (category "Good"). These results indicate that the proposed solution is effective in handling routine inquiries and can reduce customer service operational burden by 40% based on response time measurements. The main limitation lies in handling complex questions that require real-time data checking from external inventory systems.