GraphQL Interview Questions 2026, 30 Q&A on Schema, Resolvers, and Performance

By Aditya SharmaPublished 8 Jun 2026Claim-verifiedSpot an error? Corrections open

9 min read

Interview Questions

Updated: 8 Jun 2026

Aditya's Edit

PapersAdda 2026 Placement Cycle

By Aditya Sharma·Founder & Editor, PapersAdda

What changed in 2026 drives

Mass-recruiter offer letters are flatter for 2026 batch - the 4-5 LPA ASE band has barely budged in three years while inflation eats real wages. Premium tracks (Digital, Pro, Elite, Specialist) are still where the differential lives, and they are entirely test-driven. If you are aiming higher than the default offer, the coding round is not optional pageantry - it is the entire interview.

What I'd actually study for this

01Two solid coding-round answers (1 medium-hard DSA each, with edge-case discussion) > five half-baked ones
02One real project you can defend end-to-end - file paths, design decisions, and what you would change
03One DBMS schema you actually built (not a textbook ER diagram), with at least 3 join-heavy queries written from memory
04Three behavioural STAR stories: failure recovered, conflict handled, ownership taken

Where most candidates trip up

The single biggest mistake is treating company-specific guides as primary prep and DSA as secondary. It is the opposite. Mass recruiters use the test as a filter, but premium tracks at every IT services company use coding to allocate offer band. Spend 70% of prep time on DSA + system fundamentals, 20% on company-specific patterns, 10% on HR rehearsal. Reverse that ratio and you collect the default offer.

Editorial commentary by Aditya Sharma · written for PapersAdda · not generated, not aggregated.

GraphQL appears in interviews for modern API stacks, and candidates report the questions cluster around schema design, resolvers, and the N+1 performance trap. This guide compiles 30 questions from candidate-reported rounds and public preparation resources, each with schema definition language (SDL) and the trade-off being tested.

The pitch: clients request exactly the fields they need from one endpoint, avoiding over- and under-fetching. The cost: server-side complexity in resolvers, caching, and security.

Fundamentals (Q1 to Q12)

Q1. What is GraphQL?

Q2. How does GraphQL differ from REST?

	GraphQL	REST
Endpoints	One	Many
Data shape	Client-specified	Server-fixed
Over/under-fetching	Avoided	Common
Versioning	Schema evolution	URI versions
Caching	Custom	HTTP-native

Candidate-reported as a guaranteed comparison question.

Q3. What are the GraphQL operation types?

Q4. What is the schema and SDL?

type User {
  id: ID!
  name: String!
  orders: [Order!]!
}
type Query { user(id: ID!): User }

Q5. What is a resolver?

const resolvers = {
  Query: { user: (_, { id }, ctx) => ctx.db.user(id) },
  User: { orders: (user, _, ctx) => ctx.db.ordersFor(user.id) },
};

Q6. What are GraphQL scalar and custom types?

Q7. What are interfaces and unions?

Q8. What are input types?

Q9. How do mutations work?

type Mutation { createUser(input: CreateUserInput!): User! }

Q10. What are fragments?

Q11. What are variables in GraphQL?

Q12. How does GraphQL handle errors?

Performance and Resolvers (Q13 to Q22)

Q13. What is the N+1 problem in GraphQL?

Q14. How does DataLoader solve N+1?

const userLoader = new DataLoader(ids => db.usersByIds(ids));
// resolver: (parent) => userLoader.load(parent.userId)

Q15. How do you control query cost and depth?

Q16. How do you paginate in GraphQL?

Q17. How do you cache GraphQL?

Q18. What are persisted queries?

Q19. How do subscriptions work?

Q20. How do you secure a GraphQL API?

Q21. How does authorization work in resolvers?

Q22. What is schema stitching vs federation?

Scenarios and Trade-offs (Q23 to Q30)

Q23. When should you choose GraphQL over REST?

Q24. Scenario: a GraphQL endpoint is slow on a list query. Diagnose.

Q25. Scenario: a single client query overloads the server. Fix.

Q26. How do you handle file uploads in GraphQL?

Q27. How do you evolve a GraphQL schema without breaking clients?

Q28. Scenario: introspection exposes the whole schema to attackers. Mitigate.

Q29. How do you test a GraphQL API?

Q30. Scenario: design a GraphQL API for a blog with posts, authors, and comments. Walk through it.

GraphQL Mock Test, 2026 Edition

5 original questions calibrated to the 2026 backend batch by Aditya Sharma, from candidate-reported patterns.

Question 1

The N+1 problem is solved by:

a) more endpoints b) DataLoader batching c) bigger servers d) REST

Solution: DataLoader batches per-request child fetches. Answer: (b)

Question 2

GraphQL exposes:

a) many endpoints b) a single endpoint with a typed schema c) no schema d) only queries

Solution: One endpoint, client selects fields from the schema. Answer: (b)

Question 3

To prevent an expensive malicious query, use:

a) bigger timeout b) depth and complexity limits c) more caching d) HTTPS only

Solution: Limit depth/complexity and require pagination. Answer: (b)

Question 4

The standard scalable pagination in GraphQL is:

a) offset only b) cursor-based connections c) no pagination d) client filtering

Solution: Relay-style connections with cursors scale well. Answer: (b)

Question 5

To remove a field without breaking clients you:

a) delete it b) mark it @deprecated and keep it c) rename it d) change its type

Solution: Deprecate rather than remove; evolve the schema. Answer: (b)

FAQ, GraphQL Interview Questions

Q: How deep is the N+1 problem tested? Candidate-reported rounds almost always probe it and expect DataLoader as the solution.

Q: Do freshers get GraphQL questions? Lighter ones (schema, queries, resolvers). DataLoader, federation, and security depth skew mid to senior.

Q: GraphQL or REST to learn first? REST first as the default; learn GraphQL for stacks that use it. Confirm the company stack on its careers page.

Q: What is the most-missed GraphQL concept? The N+1 problem and query-cost limiting, per candidate-reported feedback.