Add-in for Office 365 Web vs Office Desktop Apps

Developing Add-in for Office 365 Web vs Office Desktop Apps

Since the release of Office 2013 and Office 365, I’ve been asked if the same plug-in developed would support both desktop and web version of Office Products. Talking to customers, many of them are left confused by what difference is between the two.

To begin with, Microsoft provides primarily two different SDKs for developing Add-ins for MS Office Tools. One SDK is called COM Add-in or VSTO Add-in SDK, and the other is called Web Apps for Office SDK, essential for Office 365 Add-in development.

What are COM-Add-ins ?

COM Add-in SDK are Windows Only Supported, hence they run only on windows desktop with Office Applications such as Word, Powerpoint, Excel or Outlook. COM Add-ins can be developed using any programming language that can interface with COM. Most COM add-in developers use Visual Studio (with C#, VB.Net, or C++) and create the UI elements with Winforms or WPF. Microsoft itself doesn’t push pure COM add-in development. Instead, they promote VSTO (Visual Studio Tools for Office), which is a layer on top of COM based SDK. COM add-ins will work in the desktop Office environment, but will not be accessible when editing a document with the web interface.

A brief into VBA Add-ins ?

Some customers also ask what are VBA Add-ins for Office. A simple answer to this is; If you want to target Office for Mac, you would need to develop in Visual Basic for Applications (VBA). VBA add-ins have limitations, especially with what you can develop in UI. Unless you have a pressing need to support old versions of Office on Mac, I would not advise to develop any VBA Add-ins.

An Intro into Apps for Office SDK.

Apps for Office SDK allows developers to develop Add-ins which would support both Desktop and Web Versions of Office Applications. It also supports Office Applications running on Mobile and Tablets. You develop Add-ins with this SDK using HTML5 / CSS3 / JavaScript and XML. You might be thinking, then why not use this SDK always. Currently the API’s available is limited in what you can access within the object model of Office Applications, hence you need to first evaluate what you need to achieve before choosing the right SDK for your business goals. Though the Web Apps Office Add-ins are accessed over the internet, you can still develop those to work offline once they have been installed.

COM Add-ins have been a pain in installation, at time the installer breaks due to a large variety of reasons. It takes a developer a couple of iterations to get a stable installer which works under all circumstances. This is resolved with new Apps for Office SDK. The Add-in is installed using a XML manifest file hosted on a web server which makes the installation process simpler, however the manifest file has to be defined correctly to cover all supported devices.