Building a REST API Rate Limiter in Node.js — From Zero to Production Rate limiting is one of those things every API needs but few get right. Here's my battle-tested implementation. Why Roll Your Own? Yes, there are middleware packages. But: express-rate-limit is basic (no sliding window) rate-limiter-flexible is powerful but complex Cloud-based solutions cost money per request Sometimes you need something simple, dependency-free, and understandable . Let's build it. The Requirements Limit requests per IP address Sliding window (not fixed window — prevents burst attacks) Redis-backed (for multi-instance support) Fallback to in-memory if Redis is down Clean HTTP headers for clients ( X-RateLimit-* ) Configurable per-route limits Step 1: The Core Algorithm class SlidingWindowLimiter { constructor ( options = {}) { this . windowMs = options . windowMs || 60000 ; // 1 minute this . maxRequests = options . maxRequests || 100 ; this .…