API Rate Limiting

API rate limiting is a strategy for controlling the frequency of requests that a user or application can make to an API endpoint. Limits are typically expressed as requests per unit of time, such as 100 requests per minute or 10,000 requests per day. When a client exceeds the limit, the server responds with an HTTP 429 Too Many Requests status code.

Rate limiting serves multiple purposes: it protects servers from being overwhelmed by excessive traffic, prevents abuse by malicious actors attempting denial-of-service attacks, ensures fair resource allocation among all API consumers, and helps manage infrastructure costs. Common implementation strategies include fixed-window counting, sliding-window logs, token bucket algorithms, and leaky bucket algorithms.

API providers communicate rate limits through response headers such as X-RateLimit-Limit, X-RateLimit-Remaining, and X-RateLimit-Reset. Developers should design their applications to respect these limits by implementing exponential backoff retry logic, caching responses to reduce redundant requests, and queuing requests during high-traffic periods. Most major APIs including those from Google, Twitter, and Stripe enforce rate limits and provide detailed documentation on their specific policies.