CartonCloud, a cloud-based Transport and Warehouse Management System, faced significant challenges in replicating production environments for local application development, resulting in complex debugging and costly AWS developer environments. To address these issues, they adopted LocalStack, a tool that emulates AWS services locally, allowing for efficient testing of serverless functions and reducing reliance on AWS. This transition, led by CTO Kenji Kimura, involved a six-month pilot project that standardized LocalStack across their development environment, significantly improving the developer experience by reducing onboarding time by almost 10 times and achieving a 15-fold increase in cost and operational efficiency. CartonCloud's innovative use of LocalStack, including the development of the Hotpotato service for optimizing API requests and SQS queue management, has enhanced the stability and efficiency of their engineering processes, transforming the onboarding and development landscape for their team.