What is REST API?
Representational State Transfer — an architectural style for building APIs that uses standard HTTP methods and URLs to perform operations on resources. The most common web API paradigm.
In plain English
A REST API is like a library system. Each book (resource) has a catalog number (URL). You can check out a book (GET), add a new book (POST), update its details (PUT), or remove it (DELETE). The operations are standard and predictable — you don't need special instructions for each book.
How it works
REST APIs expose resources at URLs (e.g., /api/users/123) and use HTTP methods to operate on them: GET to read, POST to create, PUT/PATCH to update, DELETE to remove. Responses are typically JSON. REST is stateless — each request contains all information needed to process it. Well-designed REST APIs use proper status codes, pagination, filtering, and HATEOAS links.
Why it matters for AI-built apps
Almost every web and mobile app communicates through APIs. REST is the standard that most developers, tools, and services understand. AI tools typically generate REST-style endpoints, but often with violations of REST principles — making the APIs harder to consume and maintain. Understanding REST conventions helps you evaluate and improve AI-generated code.
Common issues
Using verbs in URLs (POST /api/createUser instead of POST /api/users), returning 200 for every response regardless of outcome, not implementing pagination for list endpoints, inconsistent response formats, not using proper HTTP methods (POST for everything), and missing CORS configuration for frontend access.
Best practices
Use plural nouns for resource URLs (/users, /orders). Map HTTP methods to CRUD operations correctly. Return appropriate status codes (201 for created, 404 for not found, 422 for validation errors). Implement pagination from the start. Use consistent response envelopes. Support filtering and sorting via query parameters. Document with OpenAPI/Swagger.
Frequently asked questions
What's the difference between PUT and PATCH?
PUT replaces an entire resource (you must send all fields, even unchanged ones). PATCH partially updates a resource (you only send the fields you want to change). For most update operations in web apps, PATCH is more practical and bandwidth-efficient. AI tools often mix them up — use PATCH for partial updates.
Do I need to build my own REST API if I use Supabase?
Supabase auto-generates a REST API from your database schema, which is great for rapid prototyping. However, for complex business logic, data transformations, or multi-step operations, you'll want custom API endpoints. Many apps use a hybrid: Supabase's auto-generated API for simple CRUD and custom endpoints for complex operations.
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