What is rate limiting and how do you implement it in FastAPI?

Rate limiting protects your API from abuse and ensures fair use. For FastAPI, use slowapi (a FastAPI port of Flask-Limiter): from slowapi import Limiter; from slowapi.util import get_remote_address; limiter = Limiter(key_func=get_remote_address); app.state.limiter = limiter; app.add_exception_handler(RateLimitExceeded, _rate_limit_exceeded_handler). Apply to routes: @app.get('/api/data') @limiter.limit('10/minute') async def get_data(request: Request): .... For production with distributed instances, use a Redis backend: Limiter(key_func=get_remote_address, storage_uri="redis://localhost:6379"). For advanced scenarios, implement custom middleware that increments a Redis counter with TTL. Rate limit headers (X-RateLimit-Limit, X-RateLimit-Remaining, Retry-After) inform clients of their quota.