API Rate Limiting Algorithms Explained

Rate limiting protects APIs from abuse and ensures fair resource allocation. Understanding different algorithms helps you choose the best approach for your use case.

Token Bucket

Tokens are added to a bucket at a fixed rate. Each request consumes a token. When the bucket is empty, requests are rejected. Allows burst traffic up to the bucket size.

• Good for APIs with bursty traffic patterns
• Flexible: burst up to capacity, then throttle
• Implementation: Redis with INCR/EXPIRE

Leaky Bucket

Requests enter a queue and are processed at a fixed rate. Excess requests overflow and are rejected. Provides consistent, smooth rate limiting.

• Perfect for APIs needing constant throughput
• Smooths out traffic spikes
• Good for payment processing, serializing requests

Fixed Window

Counts requests in fixed time windows (e.g., per minute). Simple to implement but can allow double the rate at window boundaries.

Sliding Window

More accurate than fixed window. Tracks requests in a rolling time window. Complex to implement but prevents boundary spikes.

Choosing the Right Algorithm

Use Token Bucket for general APIs allowing bursts. Use Leaky Bucket for rate-sensitive operations. Use Sliding Window for precise limits without boundary effects.