Rate Limiting System Design : Explained Simply

The Backend Guide to Building Scalable Rate Limiting

Rate limiting sounds simple — until you’re asked to design it in an interview or build it for millions of users.
This post breaks down how rate limiting actually works, step-by-step, without any fluff.

This is a high-level design meant for interviews or as a foundation to explore further in real systems.

What Are We Really Solving?

Before even touching code or system diagrams, let’s understand why rate limiting is needed.

Imagine this:

You’ve built an API that gives out weather data. It works fine for a few users. But one day, someone writes a bot that hits your API thousands of times per second. Your server:

• Slows down
• Crashes
• Legit users can’t access it

Now multiply that with 10k users , some hitting it fairly, others abusing it and expensive backend services getting overloaded (like DB, external APIs).

That’s where rate limiting comes in.

Rate limiting helps you:

• Protect your system from being overwhelmed.