Mutable‑Proxy is a lightweight JavaScript library that lets you create proxies whose underlying target can be changed at runtime. It provides a factory that returns a controller with `setTarget`, `setHandler`, and the proxy itself, enabling seamless swapping of objects, arrays, functions, or class instances while preserving their original prototype behavior. The tool is aimed at developers who need dynamic, mutable proxy objects for testing, state management, or metaprogramming scenarios.