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Mock interviews by role · Software & Engineering

Full-Stack Developer mock interview

Full-stack interviews ask you to cross the boundary other candidates skip: what the screen sends, what the server stores, and what the user sees when the server is slow. An answer that is only React or only SQL is incomplete for this title.

Practice each question by naming the contract between the two sides before you pick a library.

Practice this role with an AI interviewer

What the loop usually looks like

  1. Screen

    30 min

    A feature you took from UI through the database.

  2. Practical exercise

    60 min

    A small end-to-end change: form, endpoint, and persistence.

  3. Design and collaboration

    45 min

    Trade-offs and a story about splitting work with a specialist.

What interviewers score

  • End-to-end ownership
  • API contracts
  • User-visible failure
  • Knowing when to go deep

10 full-stack developer interview questions and model answers

  1. Technical

    1. A form submit succeeds in the UI but the record never appears. How do you trace it?

    What they are testing: Crossing the stack.

    I confirm the browser sent the request and the status code. Then I check whether the handler committed, whether a background job was required, and whether the list query filters the new row out. I do not start by rewriting the form.

  2. Technical

    2. Where do you validate input: browser, server, or both?

    What they are testing: Trust boundaries.

    The browser validates so the user gets a fast message. The server validates because the browser can be skipped. Both sides share the same rules so the messages match. Authorization is only on the server.

  3. Domain

    3. How do you decide which layer owns a business rule?

    What they are testing: Boundaries.

    If the rule must hold for every client, it lives on the server next to the data. The UI may repeat it for feedback. A rule about focus or animation stays in the client.

  4. Technical

    4. Design the save flow for a note that should not be lost on refresh.

    What they are testing: Persistence and UX.

    I debounce writes to a draft endpoint and keep the latest text in the page until the save returns. The document shows saved or still saving. A failed save stays on screen with the text intact and a retry.

  5. Situational

    5. You are strong on the client and weaker on the query. How do you say that?

    What they are testing: Honest scope.

    I say which part I will implement and which part I want a reviewer on. I still sketch the query and its index so the specialist is editing a proposal, not starting from a blank page.

  6. Behavioral

    6. Tell me about a feature you shipped across UI and API.

    What they are testing: Ownership evidence.

    I name the user action, the request body, the table, and the empty state. I also name the bug we found only when both sides were together, which was a date the client sent in local time and the server stored as if it were UTC.

  7. Technical

    7. How do you keep a list and a detail page from showing different totals?

    What they are testing: Single source of truth.

    Both pages read the same query or the same aggregated field. I do not recompute the total in the client from a partial page of rows. If the list is paginated, the total comes from the server.

  8. Behavioral

    8. Describe a time you simplified the stack instead of adding a service.

    What they are testing: Restraint.

    The proposal was a new service for a weekly export. I shipped it as a job in the existing app because the data was already there and the volume was small. We agreed to split it out if the job started affecting request latency.

  9. Domain

    9. What do you ask a designer before you build a multi-step flow?

    What they are testing: Requirements.

    I ask what is saved if the user leaves at step two, and what support should see. Those two answers decide the data model. Visual polish can follow.

  10. Situational

    10. The API is late and the UI deadline is fixed. What do you show?

    What they are testing: Delivery under dependency risk.

    I ship the UI against a typed fake that matches the agreed contract, behind a flag, and I list the states the fake does not cover. I do not invent a second contract to unblock the screen.

Frequently asked questions

Are full-stack loops just two interviews taped together?

Often yes: one client exercise and one server exercise. The candidates who do well connect them instead of treating them as unrelated tests.

Should I claim full-stack if I lean one way?

Say the lean. Interviewers trust a frontend-leaning full-stack candidate who can still describe the write path more than someone who implies equal depth and then cannot.

How many projects should I talk about?

One project in detail beats three names. Bring the request, the table, and the bug.

Can I practice both sides in one session?

Yes. Set the mock up as a full-stack round and answer with the contract between UI and API. VirtualInterview.ai will follow up on the part you skipped.

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