GraphQL Interview Questions

1. What is GraphQL and how does it differ from REST?

2. What is a GraphQL schema and what is the Schema Definition Language (SDL)?

3. What is the difference between a query, a mutation, and a subscription in GraphQL?

4. What are resolvers in GraphQL and how do they work?

5. What is the N+1 problem in GraphQL and how does DataLoader solve it?

6. What are GraphQL fragments and why are they useful?

7. What is the difference between scalar types and object types in GraphQL?

8. How does GraphQL handle errors compared to REST?

9. What are GraphQL variables and how do they differ from arguments?

10. What is introspection in GraphQL and what are its security implications?

11. What is the difference between a nullable and a non-nullable field in GraphQL?

12. How does pagination work in GraphQL with cursor-based connections?

13. What are GraphQL directives and what are common built-in ones?

14. What is schema stitching and federation in GraphQL?

15. How does caching work in GraphQL and why is it harder than REST?

16. What is an input type in GraphQL and when do you use one?

17. What is the difference between over-fetching and under-fetching, and how does GraphQL address them?

18. What are GraphQL enums and interfaces and how do they differ?

19. What is a union type in GraphQL and when should you use it?

20. How do you secure a GraphQL API against malicious queries?

21. What is query complexity analysis and depth limiting in GraphQL?

22. How does the Apollo Client cache normalize data?

23. What is the difference between client-side and server-side GraphQL?

24. What are persisted queries in GraphQL and why are they used?

25. How does GraphQL versioning differ from REST versioning?

26. What is a GraphQL context object and what does it typically contain?

27. How do GraphQL subscriptions work under the hood with WebSockets?

28. What is the role of the GraphQL execution engine and how are queries resolved?

29. What is the difference between eager and lazy resolution in GraphQL resolvers?

30. How do you handle authentication and authorization in a GraphQL API?

31. How do you debug a slow GraphQL query in production?

32. How do you decide it is safe to remove a deprecated field from a GraphQL schema?

33. How do you stop a breaking GraphQL schema change reaching production?

34. How do you implement field-level authorisation in GraphQL without scattering checks through every resolver?

35. How do you model expected business errors in a GraphQL schema rather than throwing them?

36. How does an entity get resolved across subgraphs in a federated GraphQL architecture?

37. How do you scale GraphQL subscriptions across multiple server instances?

38. What are the caching and lifetime pitfalls of DataLoader in a GraphQL server?

39. How do you rate limit a GraphQL API when every request hits the same endpoint?

40. How do you test a GraphQL API across schema, resolvers and integration?

41. How do you handle file uploads in a GraphQL API?

42. How does incremental delivery with @defer and @stream work, and when is it worth using?

43. How do you cache GraphQL responses at the CDN or edge?

44. How do you implement timeouts and cancellation in a GraphQL server?

45. How do you migrate an existing REST API to GraphQL incrementally?

46. How do you make GraphQL mutations safe to retry on an unreliable network?

47. How do you stop sensitive data leaking through a GraphQL API's errors, logs and schema?

48. How do you govern a large GraphQL schema across many teams?

49. What changes when you run a GraphQL server on serverless or edge runtimes?

50. How do you load test and capacity plan a GraphQL API?

51. How do you enforce tenant isolation in a multi-tenant GraphQL API?

52. How do you keep a GraphQL client cache consistent after a mutation?

53. How do you fix an N+1 in GraphQL that DataLoader cannot batch?

54. How do you set GraphQL query cost limits without breaking legitimate clients?

55. How do persisted queries change your deployment and client release process?

56. How do you rename a GraphQL field or change its type without breaking clients?

57. Why can a single null collapse a whole GraphQL response, and how do you design against it?

58. How do you choose between offset and cursor pagination in a GraphQL schema?

59. How do you resolve schema composition conflicts in a federated GraphQL graph?

60. When should GraphQL subscriptions use server-sent events instead of WebSockets?

61. Should GraphQL authorisation live in the schema or in the resolver layer?