.ADDIN File Extension

Add-in definition file created by Microsoft Visual Studio, a Windows software development IDE; generated automatically when a new add-in project is created using the Add-In Wizard; contains data used to display the add-in information when using Visual Studio's Add-In Manager component.

ADDIN files are required in order to register new add-ins in the Add-In Manager. They are typically saved in the folder that was created for the add-in project. ADDIN files are saved using XML formatting.