Amazon's Simple Queue Service (SQS) is a cloud-based queue solution designed to help create decoupled architectures in serverless applications by ensuring that messages, such as customer orders in an e-commerce system, are processed asynchronously and reliably. SQS is particularly useful when services are loosely coupled, allowing each function to perform a single task without affecting other components. It offers a pull-based mechanism, which means subscribers must poll SQS to receive new messages, contrasting with push-based services like SNS and EventBridge. SQS guarantees at least once delivery, message persistence until consumption, and supports FIFO (first-in, first-out) queues for maintaining order. Dead-letter queues (DLQs) capture messages that fail after a specified number of retries, allowing for further investigation. AWS provides a free tier for new SQS users, offering the first one million requests per month at no cost, with pricing varying based on the type of queue and region. SQS is compatible with LocalStack, enabling users to explore and test its functionalities including debugging capabilities without triggering side effects.