The Kubernetes Scheduler is a crucial control plane component that determines which node a Pod will run on. Thus, anyone utilizing Kubernetes relies on a scheduler. kube-scheduler-simulator is a simulator for the Kubernetes scheduler, that started as a Google Summer of Code 2021 project developed by me (Kensei Nakada) and later received a lot of contributions. This tool allows users to closely examine the scheduler’s behavior and decisions. It is useful for casual users who employ scheduling constraints (for example, inter-Pod affinity) and experts who extend the scheduler with custom plugins.