The primary purpose of an API rate limiter is to control the number of requests a client can make to an API within a specified time frame. This mechanism helps prevent abuse and overload of the server, ensuring equitable resource usage among all clients. By limiting the rate of requests, API rate limiters contribute to improved performance and reliability of services while safeguarding the backend from excessive loads that could lead to downtime or impaired functionality. Rate limiting is essential for maintaining the overall health of an API ecosystem and enhancing user experience by managing resource allocation.