To create a reliable API, the performance of an API should be tested. Though the User interface of an API may be outstanding, it is the performance of the API that matters the most. The process to test the performance of an API includes load testing i.e. the memory bottleneck and data limitations.
Memory bottlenecks occur when the server is not able to handle multiple requests at a time and data limitations occur when the request posts different data from what the API expects.