How to Build an In-Memory Rate Limiter in Next.js

Rate limiters control API request frequency to prevent abuse and manage costs. This guide implements an in-memory rate limiter for Next.js using the fixed window algorithm, tracking requests by unique identifiers and blocking excess traffic with 429 responses. The implementation stores usage data in a Map, automatically clears expired entries, and can be applied to any API route. Artillery load testing confirms the limiter accurately enforces limits (12 requests per 60 seconds) even under high traffic, with 99% of requests maintaining sub-100ms latency.