Embodiments of the present invention provide a computer-implemented method for generating an API difference description file that describes the differences between multiple API versions to assist in migrating an application program from a first version to a second version. The method includes receiving a first API description file of a first version of a web API, receiving a second API description file of a second version of the web API, generating an API difference description file that describes differences between the first and second API description files, and then updating an application program using the API difference description file.