Prepare for your GraphQL interview with these 30 essential questions covering basic, intermediate, and advanced topics. Whether you’re a fresher, have 1-3 years of experience, or are a seasoned developer with 3-6 years, this guide provides clear, practical answers to help you succeed.
Basic GraphQL Interview Questions
1. What is GraphQL?
GraphQL is a query language for APIs that allows clients to request exactly the data they need, using a strongly-typed schema to define the API structure.[1][2]
2. What are the core components of a GraphQL architecture?
The main components are the schema, which defines data types and operations; resolvers, which fetch data for fields; and queries, mutations, or subscriptions for operations.[1][4]
3. How does GraphQL differ from traditional REST APIs?
GraphQL uses a single endpoint for all requests, enables clients to specify exact data needs to avoid over-fetching or under-fetching, and supports real-time updates via subscriptions.[2][5]
4. What is a GraphQL schema?
A GraphQL schema is a blueprint defining types, relationships, queries, mutations, and subscriptions using Schema Definition Language (SDL).[4][5]
5. What are scalars in GraphQL?
Scalars are primitive types like Int, Float, String, Boolean, and ID that represent leaf values in the query response.[1]
6. What is a GraphQL query?
A query reads data from the server immutably, allowing clients to request specific fields in a nested structure.[1][2]
query {
user(id: "123") {
name
email
}
}7. What are GraphQL mutations?
Mutations modify data on the server, similar to POST/PUT/DELETE in REST, and return updated data in the response.[2]
8. Explain GraphQL resolvers.
Resolvers are functions attached to schema fields that fetch or manipulate data, mapping fields to data sources with custom logic like authentication.[1][2]
9. What is introspection in GraphQL?
Introspection allows clients to query the schema itself for types, fields, and documentation, enabling tools like automatic docs and type-checking.[5]
10. What are directives in GraphQL?
Directives like @include or @skip modify query execution based on conditions, such as including fields only if a variable is true.[4]
Intermediate GraphQL Interview Questions
11. How do you define an object type in a GraphQL schema?
Use the type keyword followed by the name and fields, specifying their types, e.g., type User { id: ID!, name: String! }.[1][5]
type User {
id: ID!
name: String!
email: String
}12. What are arguments in GraphQL queries?
Arguments pass values to fields, like id: “123” in a query, to filter or customize data retrieval.[4]
13. How do you implement pagination in GraphQL?
Use cursor-based pagination with first, after, last, or before arguments, which is reliable for large or changing datasets.[3]
query {
posts(first: 10, after: "cursor") {
edges {
node { title }
}
}
}14. What are GraphQL fragments?
Fragments reuse sets of fields across queries, defined with fragment on TypeName { fields }, improving DRY principles.[1]
15. Explain input types in GraphQL.
Input types define complex arguments for mutations using input UserInput { name: String!, email: String! }, distinct from output types.[1]
16. How do you handle errors in GraphQL?
Errors appear in the errors array of the response with path, message, and extensions for precise debugging.[1]
17. What are enums in GraphQL?
Enums define a set of allowed values, like enum Role { ADMIN USER }, enforcing type safety.[1]
18. How does query validation work in GraphQL?
The server validates queries against the schema for syntax, type correctness, and cycles before execution.[1]
19. What is a union type in GraphQL?
Unions represent multiple possible types, like union SearchResult = User | Post, resolved via __typename.[1]
20. Explain interfaces in GraphQL.
Interfaces define shared fields across types, e.g., interface Node { id: ID! }, implemented by types like User.[1]
Advanced GraphQL Interview Questions
21. How do you create a custom scalar in GraphQL?
Define a scalar with name and implement serialize, parseValue, and parseLiteral functions for validation and conversion.[2]
22. What is the N+1 problem in GraphQL and how to solve it?
N+1 occurs when resolvers trigger extra queries per item; solve with DataLoader for batching and caching.[3]
23. Explain schema stitching in GraphQL.
Schema stitching merges multiple schemas into one, customizing types and fields across services using tools like GraphQL Tools.[2][3]
24. What is query complexity and how to limit it?
Complexity measures query cost to prevent overload; set limits via analyzers that score fields and depth.[3]
25. How do you implement role-based access control (RBAC) in GraphQL?
Use context in resolvers to check user roles against directives or custom logic before resolving fields.[3]
26. What are GraphQL subscriptions?
Subscriptions enable real-time updates via WebSockets, notifying clients of data changes matching a query pattern.[2][5]
subscription {
postAdded(channelId: "1") {
id
title
}
}27. How do you optimize performance in a GraphQL API?
Implement DataLoader for batching, persisted queries for caching, and query analyzers for complexity limits.[2][3]
28. Explain persisted queries in GraphQL.
Persisted queries store query strings server-side by ID, reducing payload size and enabling validation/caching.[5]
29. Scenario: At Zoho, how would you structure a large-scale GraphQL schema for a SaaS product?
Modularize into domain-specific sub-schemas, use federation for services, and apply naming conventions with interfaces for shared fields.[3]
30. Scenario: In a Paytm-like startup handling high-traffic payments, how do you debug a GraphQL API in production?
Use tracing with tools like Apollo Tracing, monitor resolver timings, log errors with paths, and set metrics for query complexity and latency.[3]
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