Sideload Office Add-ins in Office on the web for testing

You can install an Office Add-in for testing without having to first put it in an add-in catalog by using sideloading. Sideloading can be done in either Microsoft 365 or Office on the web. The procedure is slightly different for the two platforms.

When you sideload an add-in, the add-in manifest is stored in the browser's local storage, so if you clear the browser's cache, or switch to a different browser, you have to sideload the add-in again.


Sideloading as described in this article is supported on Word, Excel, and PowerPoint. To sideload an Outlook add-in, see Sideload Outlook add-ins for testing.

The following video walks you through the process of sideloading your add-in in Office on the web or desktop.

Sideload an Office Add-in in Office on the web

  1. Open Office on the web.

  2. In Get started with the online apps now, choose Excel, Word, or PowerPoint; and then open a new document.

  3. Open the Insert tab on the ribbon and, in the Add-ins section, choose Office Add-ins.

  4. On the Office Add-ins dialog, select the MY ADD-INS tab, choose Manage My Add-ins, and then Upload My Add-in.

    The Office Add-ins dialog with a drop-down in the upper right reading "Manage my add-ins" and a drop-down below it with the option "Upload My Add-in"

  5. Browse to the add-in manifest file, and then select Upload.

    The upload add-in dialog with buttons for browse, upload, and cancel.

  6. Verify that your add-in is installed. For example, if it is an add-in command, it should appear on either the ribbon or the context menu. If it is a task pane add-in, the pane should appear.


To test your Office Add-in with Microsoft Edge with the original WebView (EdgeHTML), an additional configuration step is required. In a Windows Command Prompt, run the following line: npx office-addin-dev-settings appcontainer EdgeWebView --loopback --yes. This is not required when Office is using the Chromium-based Edge WebView2. For more information, see Browsers used by Office Add-ins.

Sideload an Office Add-in in Office 365

  1. Sign in to your Microsoft 365 account.

  2. Open the App Launcher on the left end of the toolbar and select Excel, Word, or PowerPoint, and then create a new document.

  3. Steps 3 - 6 are the same as in the preceding section Sideload an Office Add-in in Office on the web.

Sideload an add-in when using Visual Studio

If you're using Visual Studio to develop your add-in, the process to sideload is similar. The only difference is that you must update the value of the SourceURL element in your manifest to include the full URL where the add-in is deployed.


Although you can sideload add-ins from Visual Studio to Office on the web, you cannot debug them from Visual Studio. To debug you will need to use the browser debugging tools. For more information, see Debug add-ins in Office on the web.

  1. In Visual Studio, show the Properties window by choosing View -> Properties Window.
  2. In the Solution Explorer, select the web project. This will display properties for the project in the Properties window.
  3. In the Properties window, copy the SSL URL.
  4. In the add-in project, open the manifest XML file. Be sure you are editing the source XML. For some project types Visual Studio will open a visual view of the XML which will not work for the next step.
  5. Search and replace all instances of ~remoteAppUrl/ with the SSL URL you just copied. You will see several replacements depending on the project type, and the new URLs will appear similar to https://localhost:44300/Home.html.
  6. Save the XML file.
  7. Right click the web project and choose Debug -> Start new instance. This will run the web project without launching Office.
  8. From Office on the web, sideload the add-in using steps previously described in Sideload an Office Add-in in Office on the web.

Remove a sideloaded add-in

You can remove a previously sideloaded add-in by clearing your browser's cache. Additionally, if you make changes to your add-in's manifest (for example, update file names of icons or text of add-in commands), you may need to clear the cache and then re-sideload the add-in using updated manifest. Doing so will allow Office to render the add-in as it's described by the updated manifest.