Set up your dev environment for extending Teams apps across Microsoft 365


Extend teams app across Microsoft 365 is currently available only in public developer preview.

The development environment for extending Teams apps across Microsoft 365 is similar to Microsoft Teams development. This article discusses specific configurations required to run preview builds of Microsoft Teams and Microsoft Office applications in order to preview Teams apps running in Outlook and Office.

To set up your development environment:

Prepare a Developer Tenant for testing

You need a Microsoft 365 developer subscription sandbox tenant to set up your dev environment. If you don't already have one, create a sandbox tenant or get a test tenant through your organization.

After you have a tenant, you need to enable sideloading for your tenant, see enable sideloading. To verify if sideloading is enabled, sign in to Teams, select Apps and then check for Upload a custom app option.

Upload a custom app option

Enroll your developer tenant for Office 365 Targeted releases


Refer to the latest updates on Microsoft Teams - Microsoft 365 Developer Blog to check if and support for Teams apps is available to your test tenant.

To enroll your test tenant for Office 365 targeted releases:

  1. Sign in to Microsoft 365 admin center with your test tenant credentials.

  2. Go to Settings > Org Settings > Organization profile.

  3. Select Release preferences.

  4. Select any Targeted release preference:

    1. Target release for everyone
    2. Target release for select users

    Microsoft 365 admin center 'Release preferences' menu with Targeted release option selected

  5. Select Save.

For more information on Office 365 release options, see Set up the Standard or Targeted release options in Microsoft 365 admin center help.

Install Office apps in your test environment


Refer to the latest updates on Microsoft Teams - Microsoft 365 Developer Blog to check if Outlook for Windows desktop support for Teams message extensions is available to your test tenant.

You can preview Teams apps running in Outlook on Windows desktop by using a recent Beta Channel build. Check if you have to Change the Microsoft 365 Apps update channel for your test tenant to install an Office 365 Beta Channel build.

To install Office 365 Beta Channel applications in your test environment:

  1. Sign in to your test environment with your test tenant credentials.

  2. Download the Office Deployment Tool and extract to a local folder.

  3. Go to the local folder and open configuration-Office365-x86.xml (or *x64.xml, depending on your environment) in a text editor and update the Channel value to BetaChannel.

  4. Open Command Prompt and navigate to the local folder path.

  5. Run setup.exe /configure configuration-Office365-x86.xml (or use the *x64.xml file, depending on your setup).

  6. Open Outlook (desktop client) and set up the mail account using your test tenant credentials.

  7. Open File > Office Account > About Outlook.
    If the build number is 14416 or higher and the channel is Beta Channel, you're running Microsoft 365 beta Channel build.

  8. In the top-right corner, turn on the Coming Soon toggle.

    'Coming Soon' toggle option in Outlook


You may need to close Outlook and restart your computer for the Coming Soon button to appear.

You can verify test tenant support for your tenant account:

  • For Teams personal tabs running on,, and Outlook for Windows desktop, sign in with your test tenant credentials and check for ellipses (...) option on the left sidebar of Office or Outlook.

    Ellipses ('...') option on the left sidebar of Outlook

  • For message extensions in and Outlook for Windows, check for More Apps option at the bottom of the Outlook compose message pane.

    'More apps' option in the Outlook compose message pane


If you're opted in to Beta Channel releases but you don't see these ellipses options, it's likely that preview feature support is in the process of rolling out to your tenant. For the latest updates, see Microsoft Teams Developer Blog.

Switch to the Developer Preview version of Teams

Ensure that you switch to the Public Developer Preview from your Microsoft Teams client.

  1. Sign in to Teams with your sandbox tenant credentials.

  2. From the ellipsis (...) menu next to your user profile, select About > Developer preview. A dialog appears, select Switch to developer preview.

  3. After the Teams app restarts, go to the ellipsis (...) menu next to your user profile and check if Developer Preview is selected.

    Public developer preview option in Teams

Install Visual Studio Code and Teams Toolkit Preview extension

Optionally, you can use Visual Studio Code to extend Teams apps into Office and Outlook.

The extension Teams Toolkit for Visual Studio Code (v2.10.0 or later) provides commands that can help modify your existing Teams code to be compatible with Outlook and Office. For more information, see enable Teams personal tab for Office and Outlook.

Next steps