Backend API

RESTful API design uses appropriate HTTP methods (GET, POST, PUT, DELETE) matched to actions, and status codes (200, 201, 400, 404, 500) to communicate results. Structure endpoints as resource-based URLs, apply consistent naming conventions, and return correct codes for success, client errors, and server errors to make your API predictable and reliable.

Implement query parameters as optional filters on GET endpoints—use `?category=electronics` for filtering, `?sort=price` for sorting, and `?page=2&limit=10` for pagination. Validate all parameters, document expected formats in OpenAPI specs, and return paginated metadata so clients can navigate results efficiently.

Configure CORS to whitelist trusted domains, implement authentication middleware (API keys, OAuth, JWT), add security headers (Content-Security-Policy, X-Frame-Options), validate all input, and enforce rate limiting. Layer these controls in your middleware stack to protect endpoints from unauthorized access and common attacks.

Yes. Version your API through URL paths (`/v1/products`, `/v2/products`) or headers, then document each version in separate OpenAPI specifications. This lets clients choose versions while maintaining clear contracts, reduces breaking changes, and enables consistent documentation across versions.

Return 400 for invalid client input, 401 for missing authentication, 403 for insufficient permissions, 404 for missing resources, and 500 for server errors. Include error messages and codes in response bodies so clients understand what failed and how to fix it.

Add rate-limiting middleware that tracks requests per client (by IP or API key) and returns 429 when limits are exceeded. Chain middleware in your server-side request handlers to validate authentication, parse parameters, and enforce policies before reaching business logic.