What is the importance of API testing and tools like Postman or Swagger?

Short answer: Ensures correctness, reliability, performance, and security of APIs. Postman → Manual and automated API testing, environment variables, collections. Swagger (OpenAPI) → Live documentation, mock servers, auto-generated client SDKs. Automates QA process and reduces bugs in production.

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.