Metacontroller is a Kubernetes add-on that enables writing custom controllers as webhook scripts in any language, without needing to write a full Go controller. It provides two primary controller patterns: CompositeController (manages child resources from a parent) and DecoratorController (attaches additional resources to existing objects matched by selectors). The system is deployed as a cluster add-on via Helm or kustomize manifests, and it runs as a controller-manager binary that watches CompositeController and DecoratorController CRDs, then calls user-defined webhooks (sync, finalize, customize) to determine desired state. The architecture is built on dynamic Kubernetes clients, shared informers with custom indexing, and a webhook executor that supports TLS mutual auth, bearer/basic auth, ETag caching, and per-endpoint configuration. Key entry points include the main binary at pkg/cmd/metacontroller/main.go, the server bootstrap at pkg/server/server.go, and the controller reconciliation loops in pkg/controller/composite and pkg/controller/decorator. External dependencies are the Kubernetes API server, etcd (for integration tests), and user-provided webhook servers. The codebase is well-structured with extensive unit and integration tests, a Helm chart, CI/CD pipelines, and active maintenance with frequent releases.