Three years ago, I woke up to a $1,200 AWS bill. Someone had found my staging API, scraped every endpoint for six hours straight, and triggered enough Lambda invocations to fund a small vacation. No rate limiting. No IP blocking. Just open season. That bill taught me more about API security than any tutorial ever could. Since then, I've built rate limiting into every API I touch—not as an afterthought, but as foundational infrastructure. I've seen credential-stuffing attacks stop cold at 100 requests per 15 minutes. I've watched DDoS attempts peter out against token buckets. I've helped teams prevent the exact disaster I stumbled into. This guide covers what I wish I'd known before that bill arrived: how to implement production-grade rate limiting, which algorithms to use when, and how to layer rate limiting with authentication and authorization so your API isn't just protected—it's defensible. Every code example here runs in production. Every attack scenario is real.…