Babel‑Contracts is a Babel plugin that adds **Design by Contract** syntax to JavaScript. It lets developers write pre‑conditions, post‑conditions, invariants and assertions directly in function bodies (using special labels), which the plugin transpiles into runtime checks that throw descriptive errors when violated; the contracts can be stripped out for production builds. The tool is aimed at JavaScript developers who want a lightweight, compile‑time‑enabled way to enforce robust API contracts and improve code correctness.