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.

1
GraphQL server can be implemented in any preferred programming language.
2
Unlike REST, where multiple endpoints provide fixed data structures, GraphQL has a single endpoint and lets clients define the structure of the response.
3
This reduces the over-fetching and under-fetching of data.
4
It is strongly typed using Schema Definition Language

Difficulty: 5/10

Topics: query flexibility, over‑fetching vs under‑fetching, schema evolution

Scenario Questions

0-2 years experience

1
How would you fetch a list of users with their posts using GraphQL compared to a typical REST endpoint?
2
If a client only needs a user's name and email, what would the GraphQL query look like and how does that avoid over‑fetching?
3
What happens if you request a field that doesn't exist in the GraphQL schema?

2-5 years experience

1
We added a new field to the User type but some clients started receiving errors; how would you debug the issue?
2
When deciding between GraphQL and REST for a new feature that requires pagination and filtering, what trade‑offs would you consider?
3
If a GraphQL resolver is causing N+1 queries, how would you identify and fix it?

5-8 years experience

1
Design a gateway that serves both GraphQL and existing REST services; how would you handle authentication and caching across the two?
2
At scale, what are the performance implications of deeply nested GraphQL queries and how would you mitigate them?
3
How would you implement rate limiting for a public GraphQL API without impacting existing REST clients?

8+ years experience

1
Our 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.
2
When multiple teams own different parts of the schema, how do you enforce versioning and backward compatibility?
3
What 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?