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What are apps for Office?
Apps are web applications that extend what a document, email message, or meeting request can do in Office.
Run them in multiple environments like Office desktop applications, Office Online, and mobile browsers—in the cloud or on your site.
API Tutorial for Office
The API Tutorial is a great way to start building apps for Office. The app teaches you how to get basic development tasks done in an interactive way by allowing you to run and edit code directly in Microsoft Excel. You can download the app for free from the Office Store, or run it online.