The core Composite Application Framework client-side JavaScript library, automatically included into every Composite Application Framework HTML page, is built on the open-source Prototype library. Prototype provides many convenience functions for manipulating strings, arrays, and DOM objects, as well as for making asynchronous requests. See Using Prototype.js for documentation on the Prototype library.

The core Composite Application Framework library provides a few extra prototype-style convenience functions, a facility for logging debug messages, a facility for dynamically loading other script files, a facility for displaying alert and progress dialogs, access to the Client-Side Model, and access to the Scriptaculous Effects library.