1. A non-transitory machine-readable storage medium comprising instructions executable by a processor of a computing device for classifying application protocol interfaces (APIs) to: determine that a user action occurred; monitor a first thread separate from a user interface (UI) thread of the computing device, where the first thread processes a first application programming interface (API) in response to the occurrence of the user action; determine whether the first API being processed on the first thread is related to the user action; responsive to the first API being related to the user action, determine whether the first API being processed on the first thread causes the first thread to update the UI thread of the computing device; and responsive to the UI thread being updated, tag the first API as affecting user experience.