A method for ranking a set of APIs for multiple software applications executing on respective servers, including initializing, by a first computer, respective ranking scores for the APIs, and receiving, from a plurality of second computers, multiple API calls to the APIs in the set. For each given API call to a given API in the set received from a given second computer, a given server executing a given software application including the given API is identified, the given API call is forwarded to the identified server, a response to the given API call is received from the identified server, performance metrics with respect to the given API call and response are computed, and the ranking score for the given API are updated based on the computed performance metrics. The APIs can be provided to the second computers responsively to the ranking scores, as updated in response to the requests.