---
title: GraphQL Interview Questions & Answers (2026): Queries, Resolvers & vs REST
description: The GraphQL interview questions that get asked in 2026 — queries vs mutations, the schema, resolvers, GraphQL vs REST and the N+1 problem — with clear answers.
url: https://usegreenroom.app/blog/graphql-interview-questions
last_updated: 2026-06-19
---

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Technical

# GraphQL interview questions and answers

June 19, 2026 · 8 min read

![GraphQL interview questions and answers — cover from Greenroom, the AI mock interviewer](/assets/blog/graphql-interview-questions-hero.webp)

GraphQL is a popular alternative to REST for APIs, and its interviews test why it exists (precise data fetching), how the schema and resolvers work, and the trade-offs versus REST. Here are the **GraphQL interview questions** that actually get asked, with answers. (See also our REST API guide.)

## Fundamentals

- What is GraphQL, and what problem does it solve?
- **GraphQL vs REST** — over-fetching and under-fetching.
- Queries vs **mutations** vs subscriptions.
- What is the schema and the type system (SDL)?
- Single endpoint — why?

## Resolvers & execution

- What is a **resolver** and how does it work?
- The resolver chain; how nested queries resolve.
- Arguments and variables.
- Fragments.

![GraphQL interview topics — queries, mutations, schema, resolvers, vs REST](/assets/blog/pool-structured-screen.webp)

GraphQL rounds test the schema/resolver model and the trade-offs versus REST.

## Performance & practical concerns

- The **N+1 problem** in GraphQL and how DataLoader solves it.
- Caching challenges compared to REST.
- Error handling and partial responses.
- Security — query depth limiting, rate limiting.

**The core truth:** GraphQL interviews reward understanding the trade-off — it gives clients precise control over data and eliminates over-fetching, but complicates caching and can introduce N+1 problems. Knowing when it beats REST, and when it doesn't, is the signal.

## How to prepare

GraphQL rounds probe the model and trade-offs versus REST. Practise explaining resolvers and the N+1 fix out loud. Greenroom runs spoken technical interviews that follow up on your reasoning. Pair it with our REST API and backend guides.

## Frequently asked questions

### What are the most common GraphQL interview questions?

Common GraphQL questions cover what GraphQL is and the problems it solves, GraphQL vs REST (over-fetching and under-fetching), queries vs mutations vs subscriptions, the schema and type system, the single endpoint, resolvers and the resolver chain, arguments, variables and fragments, the N+1 problem and DataLoader, caching challenges, error handling, and security like query depth limiting.

### What is the difference between GraphQL and REST?

REST exposes multiple endpoints that each return fixed data structures, which can cause over-fetching (getting more than you need) or under-fetching (needing multiple requests). GraphQL exposes a single endpoint where the client specifies exactly which fields it wants in one query, eliminating over- and under-fetching. The trade-off is that GraphQL complicates HTTP caching and can introduce N+1 query problems.

### What is the N+1 problem in GraphQL?

The N+1 problem occurs when resolving a list field triggers one query for the list and then a separate query for each item's nested data, resulting in N+1 database calls. It's solved with batching and caching via a tool like DataLoader, which collects the individual requests within a tick and resolves them in a single batched query, dramatically reducing database round trips.

### How should I prepare for a GraphQL interview?

Focus on the schema and resolver model, the trade-offs versus REST (precise fetching vs harder caching), and performance concerns like the N+1 problem and DataLoader. Practise explaining how resolvers work and when GraphQL beats REST out loud with a voice-based mock interview that follows up, since these rounds probe understanding and trade-offs rather than syntax.

GraphQL rounds reward understanding the trade-offs, explained out loud. Greenroom runs spoken technical interviews that follow up on your reasoning. Free to start.