Granularity: Microservice APIs should be designed with a clear Single?

Short answer: Responsibility Principle (SRP) in mind, meaning each microservice should expose only the functionality related to its domain. Avoid "fat" endpoints that do too much.

Real-world example (ShopNest)

ShopNest splits Catalog, Cart, Order, and Payment into services so teams can deploy catalog changes without redeploying payments.

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.