1. An application programming interface (API) analytics system comprising: a memory comprising API call data that identifies a set of API calls detected during performance of an activity, and a classification structure that maps predetermined API usage patterns to predetermined types of activities, the classification structure comprising a plurality of nodes connected by a plurality of branches, the nodes representing tests, the branches representing outcomes of the tests, leaf nodes of the nodes representing the predetermined types of activities; and a processor configured to: form truncated API call data in which duplicated API calls in the set of API calls are consolidated in the truncated API call data; and classify the activity as one of the predetermined types of activities based on a traversal of at least one of the branches of the classification structure to a leaf node that represents the one of the predetermined types of activities, the traversal governed by an application of a set of the tests to the truncated API call data, the set of the tests including any of the tests represented by any of the nodes on a path that includes the at least one of the branches of the classification structure and that ends at the leaf node.