Engineering · Interview Prep
Full-Stack Developer Interview Questions
Full-stack interviews probe breadth with real depth spikes. Expect a live feature build that touches frontend, API, and DB in one session, plus a system-design round where you own every layer. This guide shows the questions that separate 'ships features' from 'owns products.'
Try AI Interview PrepTypical loop
2–4 weeks from first contact to offer (faster than specialists)
Difficulty
High
Question count
13+
Typical interview loop
Full-stack loops lean on end-to-end ownership rounds. Startups often run a take-home (build a small app) followed by an in-person extension. Mid-size companies run a single onsite live build where you ship a feature across layers in 90 minutes. Senior candidates face system-design rounds spanning React state, API contracts, and DB schema.
- 1Recruiter screen (30 min)
- 2Technical phone screen (60 min, often a take-home alternative)
- 3Onsite: full-stack live build (UI + API + DB in one round)
- 4Onsite: system design spanning frontend, backend, and data model
- 5Onsite: debugging or code-review round
- 6Onsite: behavioral with hiring manager
13 real full-stack developer interview questions
How to approach this
The classic full-stack warm-up. Interviewers grade the end-to-end choices: REST vs. RPC, optimistic UI updates, error rollback, and how you model the DB. Use a single DB table (id, text, completed, created_at), a thin Express/FastAPI handler layer, and TanStack Query on the client with optimistic updates + onError rollback. Discuss why optimistic UI matters for perceived performance.
STAR outline
- Situation
- 90-minute onsite: build a working todo app with persistence, tests, and deploy-readiness.
- Task
- Ship a working feature across UI, API, and DB that passes manual QA and has at least one test at each layer.
- Action
- Scaffolded with Vite + Hono + SQLite. Wrote the DB schema first, then an OpenAPI-generated client. Added TanStack Query with optimistic mutations and rollback on 4xx. Wrote a Playwright smoke test and a server-side unit test. Deployed to Fly.io to prove the loop works.
- Result
- Interviewer said the optimistic rollback and the deployment were the two differentiators from other candidates.
Common mistakes
- Building the UI first, then realizing the API shape doesn't fit — design the contract first
- No optimistic UI, making the app feel slow even when the code is correct
- Skipping tests entirely — interviewers expect at least one test per layer
Likely follow-ups
- How would you handle offline support?
- What if this needs to scale to 1M users per day?
General interview tips
- ·In live builds, always ship one test per layer — a unit test on the API, a Playwright happy-path on the UI. It's the cheapest way to signal rigor.
- ·Full-stack system design is graded on end-to-end flow. Draw the request arrow from user click → network → server → DB → response → UI update, and label each hop with latency budget.
- ·Know your deployment story. 'I'd push to Vercel / Fly / Railway with a preview URL per PR' beats 'someone else handles deploys' every time.
- ·For AI-tool-assisted questions in 2026, show your verification loop: generate, read, test, keep. Interviewers reject candidates who either refuse to use AI or accept its output uncritically.
- ·When you hit a dead end in a coding round, say the layer you're stuck on and what you'd check next. 'Stuck on the cache invalidation — let me check if TanStack Query's staleTime is the issue' is great signal.
FAQ
How much depth do I need per layer as a full-stack candidate?
Breadth with depth spikes. You need working-level depth everywhere and expert depth in at least one area. Senior full-stack roles expect you to answer backend-specialist-level questions in at least one layer (typically backend or DB) while maintaining solid frontend craft.
Should I prepare system design differently than a backend candidate?
Yes. Full-stack system design spans UI state, API contract, and data model in one diagram. Practice designing features (chat, feed, dashboard) where you articulate the client state management and the server design together, and always map network calls to user interactions.
Is it worth doing take-homes for full-stack roles?
Often yes. Many startups and mid-size companies prefer take-homes for full-stack because they show real product thinking across layers. Invest 4–8 hours on a take-home if you're serious about the role; budget zero if it's open-ended with no time cap. Always ship a README explaining your trade-offs.
What stack should I assume for interview prep?
React + TypeScript on the frontend, Node/Express or Python/FastAPI on the backend, Postgres + Redis on data. That combo covers 70% of US full-stack roles in 2026. If the role is Next.js-forward, add App Router and server actions. If it's Rails or Django, prep accordingly — but the design-thinking skills transfer.
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