Full-stack Developer interview questions and answers.

Questions

Technical questions to practise out loud

1. 01

   How do you design a clear API?

   A clear API models domain resources and operations consistently, validates inputs, uses predictable status and error formats, supports pagination and idempotency where needed, and evolves through an explicit compatibility policy.

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2. 02

   How do you handle transactions across services?

   Do not stretch a database transaction across services; keep each local transaction atomic and coordinate the workflow with idempotent commands, durable events, retries, compensation, and an observable state machine.

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3. 03

   What is the difference between authentication and authorization?

   Authentication proves who the caller is; authorization decides what that identity may do on a specific resource. Authenticate first, then enforce least-privilege authorization on the server for every protected operation.

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4. 04

   How do you keep frontend and backend contracts aligned?

   Keep contracts aligned with one versioned schema such as OpenAPI, generate or validate clients where useful, add consumer and provider contract tests, and deploy backward-compatible changes before removing old fields.

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5. 05

   How do you trace a request across the stack?

   Propagate a correlation or trace ID from browser to API and downstream services, record distributed spans and structured logs, and connect frontend timings, backend latency, errors, and release metadata in one trace.

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6. 06

   Where do you cache in a full-stack application?

   Cache at the layer that owns freshness: HTTP/CDN for public responses, client caches for server state, and backend caches for expensive shared reads. Define keys, TTL, invalidation, stampede protection, and stale-data tolerance first.

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7. 07

   How do you secure a full-stack application?

   Secure every boundary: validate untrusted input, authenticate securely, authorize server-side, protect sessions and CSRF, encode output, use parameterized queries, manage secrets outside code, and patch dependencies from a threat model.

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8. 08

   What is your end-to-end testing strategy?

   Use unit tests for domain logic, integration tests for databases and APIs, contract tests between frontend and backend, and a small end-to-end suite for critical journeys; keep failures attributable and test data isolated.

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9. 09

   How do you diagnose a slow user journey?

   Trace the complete user journey before optimizing: measure browser rendering and network waterfalls, follow the request through services and queries, identify the dominant latency component, fix it, and compare the same percentile baseline.

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10. 10

    How do you release a full-stack feature safely?

    Release a full-stack change with backward-compatible API and database steps, automated checks, feature flags or progressive rollout, health and business monitoring, and a tested rollback that does not depend on reverting irreversible data changes.

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