API Rate Limiting: Algorithms, Headers & Best Practices

How to implement API rate limiting: token bucket, sliding window, leaky bucket algorithms. With headers and response codes.

Rate Limiting Algorithms

• Fixed window: Simple but allows bursts at window boundaries
• Sliding window: Smoother distribution, slightly more complex
• Token bucket: Allows bursts up to bucket size, then throttles. Most common.
• Leaky bucket: Processes at constant rate, queues excess requests

Response Headers

X-RateLimit-Limit: 100\nX-RateLimit-Remaining: 23\nX-RateLimit-Reset: 1711120060\nRetry-After: 30  // on 429 responses

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