REST API Overview

REST (Representational State Transfer) uses HTTP methods (GET, POST, PUT, DELETE) with resource-based URLs. Each endpoint returns fixed data structure, requiring multiple requests for related data. REST is simple, well-understood, cacheable with HTTP caching, and supported by all platforms. However, it often leads to over-fetching (getting unnecessary data) or under-fetching (requiring multiple requests).

GraphQL Fundamentals

GraphQL is a query language for APIs where clients specify exactly what data they need. Single endpoint handles all requests, strongly typed schema defines available data, queries can fetch nested related data in one request, and mutations handle data modifications. GraphQL eliminates over-fetching and under-fetching but adds complexity in implementation and caching.

Mobile apps using GraphQL report 40% reduction in network requests and 60% less data transfer compared to REST.

Data Fetching Efficiency

REST example: Fetching user profile with posts requires 2-3 requests (GET /users/123, GET /users/123/posts, GET /posts/456/comments). GraphQL: Single query fetches user, posts, and comments in one request. For mobile apps on slow networks, reducing round trips significantly improves perceived performance. However, complex GraphQL queries can be slower than optimized REST endpoints.

Caching Strategies

REST benefits from HTTP caching (ETags, Cache-Control headers) and CDN support. GraphQL caching is more complex: Apollo Client provides normalized cache, queries are POST requests (not cacheable by default), and persisted queries enable GET requests for caching. Implement custom cache keys and cache invalidation strategies for GraphQL.

Offline Support

Both support offline-first architecture. REST with local database and sync queue works well. GraphQL with Apollo Client offers optimistic UI updates, automatic retry on reconnection, and conflict resolution. GraphQL's normalized cache makes offline support more elegant but requires more setup. Choose based on your team's expertise and app complexity.

Performance Comparison

GraphQL reduces network requests (fewer round trips) and data transfer (precise queries), but has higher server complexity and potential N+1 query problems. REST has simpler server implementation, better HTTP caching, and predictable performance, but requires more client-side data management. For mobile apps, GraphQL often wins on slow networks despite server overhead.

When to Use Each

Choose GraphQL when: You have complex, nested data relationships, mobile app needs flexible data fetching, you want to avoid versioning, or you're building multiple clients (iOS, Android, Web) with different data needs.

Choose REST when: You have simple, flat data structures, you need maximum HTTP caching, your team lacks GraphQL expertise, or you're building a public API for third-party developers who expect REST.