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API Rate Limit

A restriction on the number of API requests a client can make within a specified time period.

Sep 8, 2026 / About 1 min read

Security

An API rate limit is a control mechanism that restricts the number of requests a client can make to an API within a defined time window. Rate limiting protects services from abuse, ensures fair resource allocation among users, and prevents individual clients from overwhelming the system with excessive requests.

Rate limiting is implemented using algorithms such as the token bucket, sliding window, or fixed window counter. The token bucket algorithm allows short bursts of traffic while maintaining an average rate limit. Rate limit information is communicated to clients through HTTP headers such as X-RateLimit-Limit, X-RateLimit-Remaining, and Retry-After.

For URL shortening services, rate limiting applies to multiple endpoints: link creation (to prevent spam), redirect handling (to mitigate DDoS attacks), analytics queries (to protect database resources), and bulk operations (to manage server load). Different endpoints may have different rate limits based on their resource consumption.

When a client exceeds the rate limit, the server responds with HTTP 429 (Too Many Requests) and a Retry-After header indicating when the client can resume making requests. Well-designed APIs provide clear documentation of rate limits and graceful error responses.

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Related Terms

Bulk Shortening

The ability to shorten multiple URLs at once, typically through a CSV upload or API batch request.

Input Validation

The process of verifying whether input data from users matches the expected format and range. One of the security measures.

HTTPS

The secure version of HTTP that encrypts data transmitted between a browser and a web server using TLS.

Rate Limiting

A mechanism that caps the number of requests to an API or service within a given time window. Protects servers and ensures fair usage.

API Key

A unique string used to authenticate and control access to a web API. Identifies the caller and enforces usage limits.

SPF / DKIM

Technologies that authenticate email sender domains. DNS-based mechanisms essential for preventing spoofed and phishing emails.

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FAQ

How are API rate limits implemented?
Common algorithms include token bucket, sliding window, and fixed window. An in-memory data store such as Redis can be used to count requests.
What response should be returned when a rate limit is reached?
Return an HTTP 429 (Too Many Requests) status code. Include a Retry-After header to indicate when the client can retry, enabling proper backoff behavior.

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