What is GraphQL, and how does it differ from REST?
GraphQL is a query language for your API, and a server-side runtime for executing queries using a type system you define for your data. The GraphQL specification was open-sourced in 2015 and has since been implemented in a variety of programming languages. GraphQL has been released simply as a specification, for a query language for APIs that allows clients to request exactly the data they need, nothing more and nothing less.
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GraphQL server can be implemented in any preferred programming language.
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Unlike REST, where multiple endpoints provide fixed data structures, GraphQL has a single endpoint and lets clients define the structure of the response.
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This reduces the over-fetching and under-fetching of data.
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It is strongly typed using Schema Definition Language
Scenario Questions
0-2 years experience
- 1How would you fetch a list of users with their posts using GraphQL compared to a typical REST endpoint?
- 2If a client only needs a user's name and email, what would the GraphQL query look like and how does that avoid over‑fetching?
- 3What happens if you request a field that doesn't exist in the GraphQL schema?
2-5 years experience
- 1We added a new field to the User type but some clients started receiving errors; how would you debug the issue?
- 2When deciding between GraphQL and REST for a new feature that requires pagination and filtering, what trade‑offs would you consider?
- 3If a GraphQL resolver is causing N+1 queries, how would you identify and fix it?
5-8 years experience
- 1Design a gateway that serves both GraphQL and existing REST services; how would you handle authentication and caching across the two?
- 2At scale, what are the performance implications of deeply nested GraphQL queries and how would you mitigate them?
- 3How would you implement rate limiting for a public GraphQL API without impacting existing REST clients?
8+ years experience
- 1Our organization wants to migrate a large monolithic REST API to GraphQL over several years; outline a migration strategy that minimizes disruption for multiple product teams.
- 2When multiple teams own different parts of the schema, how do you enforce versioning and backward compatibility?
- 3What governance model would you set up to manage schema evolution and avoid breaking changes across services?
Follow-up Questions
- Can you give an example of a query that would be inefficient in GraphQL?
- How does caching differ between GraphQL and REST?
- What are the security considerations unique to GraphQL?