Expression‑Expander is a tiny TypeScript/JavaScript library that recursively walks any object graph (objects, arrays, maps, sets, primitives, promises, etc.) and replaces template strings of the form `${…}` with values looked up (or otherwise evaluated) from a user‑supplied context. It’s aimed at developers who need lightweight, configurable string interpolation inside configuration objects, JSON‑like data structures, or any nested data before runtime.