How would you ensure that a REST API is idempotent?

Short answer: GET, PUT, DELETE → Ensure repeated requests produce the same result. Avoid side effects on repeated requests. Use unique request IDs for POST (to prevent duplicate creation).

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.