What’s new for Office Add-ins: Announcements from Build 2023  

Office Add-ins team

The Microsoft 365 ecosystem is expanding rapidly, and we’re seeing an increasing number of add-in solutions across Office applications. We value your feedback and are committed to delivering new capabilities to help you build more powerful integrations with Word, Excel, PowerPoint, and Outlook. In this blog, we explore the new capabilities and features available to empower your Office solutions even more.  

Word 1.5 JavaScript API requirement set 

The Word 1.5 JavaScript API requirement set is rolling out to production! These new APIs streamline important scenarios such as citation management, document assembly and so on. Additionally, the APIs also provide performance improvements within Word compared to the features available using the OOXML APIs. For more information, see Word 1.5 requirement set and view the on-demand video Build with Microsoft Word as a platform: Word JavaScript APIs and key user scenarios.

Diagram showing what's new in Word 1.5 JavaScript API

These APIs extend and enrich the following areas. 

  • Insert file content from a Base64 format and keep original settings of footnote, endnote, page border, style, watermark, track changes and so on. Use these APIs to import a template with rich format, generate content, etc.
  • Import styles from other files and apply them to current working document. Use these APIs to store company-defined or individual-defined styles into documents and reuse them when needed.  
  • Manage footnote and endnotes of a document.  
  • Manage four types of fields across platforms: ADDIN, DATE, HYPERLINK, and TOC.  
  • Save and close a document.  
  • Fire events on add, delete, enter, exit, change data, or change selection of rich text content controls. With these events, add-ins can provide more interactive experience for end users. For example, show different content to users when they navigate among rich text content controls. 
  • Plain text content controls are supported across platforms. Now you can add, update or delete plain text content controls.  

With Word API 1.5, many user scenarios can be enhanced or unlocked. For example, citation management scenario is now unblocked with the support of Field, Footnote / Endnote, and Content Controls. Assembling documents is much easier with Styles, file insertion, Fields and Content Control support.  

Support for add-ins in the new Outlook on Windows

Every year, we focus on delivering features you need to enhance your Outlook add-ins and enable experiences not possible before. With the new Outlook on Windows client in preview, we’re launching initiatives to help ensure that your add-in solutions integrate seamlessly.

Microsoft Outlook modern web interface

The new Outlook on Windows desktop client in preview unifies the Outlook experience across platforms into a single web codebase. This creates a beautiful, modern interface that delivers a more consistent user experience with faster access to feature updates.  

Already have an existing Outlook web add-in? We invite you to test it in the new Outlook on Windows client and share your feedback on your experience with us and the developer community. 

Given the web-based nature of the new Outlook on Windows client, VSTO and COM add-ins aren’t supported. We recognize that there are some scenarios that can currently only be implemented in VSTO and COM add-ins. To help you plan and transition your existing solution to a web add-in, we’re focusing on closing this gap and developing support for these scenarios in web add-ins. This way, your users can continue to use your add-in solution in the new Outlook on Windows client. 

To learn more about the web add-in experience in the new Outlook on Windows client, see Develop Outlook add-ins for the new Outlook on Windows (preview) and view the on-demand session Unleash your Outlook Add-ins experiences into the new Outlook.

Mailbox 1.13 JavaScript API requirement set 

As part of the effort to close the gap on scenarios only supported by VSTO and COM add-ins, we’re excited to share that some of these features are now generally available in Outlook on Windows and on the web with the release of Mailbox 1.13.  

  • Set custom signatures with the OnMessageFromChanged and OnAppointmentFromChanged events. With the addition of these events to the event-based activation feature, your add-in can update the signature when the sender’s account changes.
  • Schedule messages to send at a later date, even with the Outlook client closed, using the delay delivery time API. 
  • Activate your add-in and perform operations on multiple selected messages in one go with the item multi-select feature. Now you can complete certain operations with a single click, such as uploading emails to your customer relationship management (CRM) system or categorizing items in your inbox. 
  • Activate your add-in even without the Reading Pane enabled or a message first selected from the mailbox by configuring the SupportsNoItemContext element in your manifest. Enable users to access content from different data sources, such as SharePoint or OneDrive, directly from their Outlook client. 
  • Automatically prepend marketing headers and legal disclaimers to a mail item when it’s sent with the prepend-on-send feature. 
  • Implement data loss prevention solutions through the sensitivity label API. With this API, it’s possible to develop an add-in to automatically assign and verify the sensitivity label of a mail item to ensure that it’s only shared with authorized stakeholders. This feature also introduces the OnSensitivityLabelChanged event, so that your add-in can automatically detect changes to the sensitivity label and perform operations as needed. 
  • Activate an add-in in shared mailbox scenarios by configuring the SupportsSharedFolders element in your manifest. 

The sample scenarios outlined for each feature provide a glimpse into what your add-in can achieve. Using these new features, the possibilities to address other use cases are endless. Unlock these capabilities in your Outlook add-in with Mailbox 1.13 today! 

Discover new add-in capabilities in Outlook on mobile devices  

We continue to enhance the Outlook add-in experience across all platforms and we’re pleased to share new and upcoming capabilities in Outlook on Android and on iOS. As a result, you can empower your users to do more on your Outlook mobile add-ins.

  • Never miss notes from a meeting ever again! Enable your add-in to directly log appointment notes and other meeting details to an external system, such as a CRM or note-taking application. With this feature, your add-in will activate in the Appointment Read surface and will implement a Log button. To learn how to implement this feature, see Log appointment notes to an external application in Outlook mobile add-ins. 
  • Support for event-based activation is expanding to Outlook mobile, starting with the OnNewMessageCompose event. Stay tuned for more information about this feature in the coming months! 

Excel 1.17 JavaScript API Set 

Excel is the ultimate decision-making tool. Add-ins extend Excel’s data analysis, calculation, and visualization capabilities.  We see a ton of success from existing add-ins and many new add-ins are focused on bringing the power of AI to users. We have over 2000 APIs available for Excel, and we’ve added a few more that enable your add-ins to work with conditional formatting and handle changes to worksheet properties. The Excel API 1.17 requirement set includes multiple new methods for adjusting conditional formatting rules and worksheet events:  

  • The additional Change conditional formatting rules APIs allow you to adjust the conditional format rule to different types like cell value, color scale, text comparison, etc. You can also remove the format properties from a conditional format rule with clearFormat() API.  
  • The Worksheet events APIs allow you to monitor changes to the name, visibility, and position of a worksheet. You can customize your add-in action based on these events.  

 For more information, see Excel JavaScript API 1.17.       


We hope you are as excited about these new features as we are. Take a moment to learn more and engage with us! 

Happy coding! 


Discussion is closed. Login to edit/delete existing comments.

  • PandaSharp 3

    I’d love just one feature for the new Outlook, use native instead of web tech and avoid use 500mb of Ram to do nothing.

  • Richard Deeming 1

    We need to replace a COM add-in which automates saving a message (as a .msg file) and its attachments to configured folders on the user’s network.

    As far as I can see, that’s something that will never be possible with a web add-in. JavaScript has no access to the user’s file system, beyond an extremely limited and isolated local folder exposed by the File System API.

    Is there a suggested workaround for this scenario? Or are we just going to have to tell our customers to never update Outlook?

  • MgSam 1

    Who is “Outlook on Windows” for? Why do you guys keep building new mail clients every few years?

    Instead of building a new client, please improve the existing Outlook which is already used by millions of your paying customers. How about implementing sorting and easier exporting on a meeting attendee list? How about making a rules UI which is easier and more intuitive to use?

  • Steve 1

    I don’t get why we need this new web-based outlook client instead of using the outlook website directly.
    The web-based tech comes with its own limitations and can never replace existing native COM add-ins.
    Besides, the new outlook client takes ages to start (10s is already an unacceptable level) and eats extensive memory. Do you think I should appreciate the beautiful splashing screen and placeholders for 10s before I start checking emails?
    Please stop producing such web-based garbage app because no one wants a client that costs more to do less.

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