text: Private API A private API is an interface that opens parts of an organization's backend data and application functionality for use by developers working within (or contractors working for) that organization. Private APIs are only exposed to internal developers therefore the API publishers have total control over what and how applications are developed. Private APIs offer substantial benefits with regards to internal collaboration. Using a private API across an organization allows for greater shared awareness of the internal data models. As the developers are working for (or contracted by) one organization, communication will be more direct and therefore they should be able to work more cohesively as a group. Private APIs can significantly diminish the development time needed to manipulate and build internal systems that maximise productivity and create customer-facing applications that improve market reach and add value to existing offerings.
  Private APIs can be made "private" in a number of ways. Most commonly the organization simply chooses not to document such an interface, such as in the case of undocumented functions of Microsoft Windows, which can be found by inspection of the symbol tables. Some Web-based APIs may be authenticated by keys, both discoverable by analysis of application traffic. macOS furthermore uses an "entitlement", granted only by digital signature, to control access to private APIs in the system.
  Private APIs are by definition without any guarantee to the third-party developer choosing to uncover and use them. Nevertheless, the use of undocumented functions on Microsoft Windows have become so widespread that the system needs to preserve old behaviors for specific programs using the "AppCompat" database.