A restriction on the number of API requests a client can make within a given time period, used to protect server resources and ensure fair access.
Rate limiting prevents any single client from overwhelming an API with too many requests. Common limits are expressed as requests per second, per minute, or per day. When a client exceeds the limit, the API returns an error (typically HTTP 429 Too Many Requests) and the client must wait before making more requests.
Rate limits vary by API and by access tier. Public APIs often have lower limits; registered or paid users may have higher limits. Understanding rate limits is important when building applications that make many API calls.
Example: An open data API allows 100 requests per minute for anonymous users and 1,000 requests per minute for registered users. A developer building a data pipeline that needs to retrieve 50,000 records must design their code to respect the rate limit — for example, by adding delays between requests or batching queries to stay within the allowed rate.