Rate Limiting

Core Idea

Rate limiting defines a quota, such as “100 requests per minute,” and rejects additional calls with HTTP 429. Implementations rely on counters tied to an identifier (IP, API key, token) and a rolling or fixed time window. When the quota resets the client can send requests again.

Why It Matters Here

FastAPI tutorials often pair rate limiting with shared state—Redis, API Gateways, or proxies—to keep counts consistent across workers. Integrating it with CORS preflight handling ensures abusive browsers never reach expensive handlers, and storing counters in a Redis cache prevents per-process drift.