Stripe Backend Engineer Interview Questions

I would isolate the dependency behind a clear boundary, degrade gracefully, and surface status honestly to the caller. Depending on the operation, I might queue the request for later processing, retry with backoff, or switch to a safe fallback state. The system should remain internally consistent even when the upstream network is not.

I would instrument request traces, business metrics, audit logs, and alerting around key invariants such as duplicate attempts, failed captures, and reconciliation gaps. Observability in payments is not just about latency; it is about being able to explain where every important operation went. If something is wrong, the system should make the failure path visible quickly.

I would treat backward compatibility as a core contract and avoid breaking existing clients without a migration path. That means adding fields instead of changing meanings, versioning carefully, and deprecating old behavior gradually. For a payments company, stable APIs are essential because clients often integrate deeply and cannot update instantly.

I would combine unit tests for business rules, integration tests for persistence and external dependencies, and end-to-end tests for the most critical flows. I would also add failure injection and idempotency tests because those are where payment bugs often hide. The test plan should focus on preventing financial correctness regressions, not just code coverage.

I would treat refunds and reversals as first-class financial operations with their own state and audit trail. They should never mutate the original charge record in a way that hides history; instead, they should create compensating entries that clearly explain the correction. That makes reconciliation and support investigations much safer.