Registry entries for VSTO Add-ins
Applies to: 
Visual Studio 
Visual Studio for Mac
Note
This article applies to Visual Studio 2017. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here
You must create a specific set of registry entries when you deploy VSTO Add-ins that are created by using Visual Studio. These registry entries provide information that enables the Microsoft Office application to discover and load the VSTO Add-in.
Applies to: The information in this topic applies to VSTO Add-in projects. For more information, see Features available by Office application and project type.
Note
Interested in developing solutions that extend the Office experience across multiple platforms? Check out the new Office Add-ins model. Office Add-ins have a small footprint compared to VSTO Add-ins and solutions, and you can build them by using almost any web programming technology, such as HTML5, JavaScript, CSS3, and XML.
When you build your project, Visual Studio creates these registry entries on the development computer. This helps you easily run and debug the VSTO Add-in. Using ClickOnce to deploy your VSTO Add-in, the registry entries are automatically created on the end-user computer.
For more information about how to deploy a VSTO Solution Using Windows Installer, see Deploying a VSTO Solution Using Windows Installer.
For more information about how the registry entries are used during the load process for VSTO Add-ins, see Architecture of VSTO Add-ins.
Note
In this topic, the text add-in ID represents a unique ID for your VSTO Add-in. By default, the ID is the name of your VSTO Add-in assembly.
Register VSTO Add-ins for the current user vs. all users
When a VSTO Add-in is installed, it can be registered in two ways:
For the current user only (The VSTO Add-in is available only to the user that was logged onto the computer when the Add-in was installed). In this case, the registry entries are created under the HKEY_CURRENT_USER.
For all users (that is, any user that signs in to the computer can use the VSTO Add-in). In this case, the registry entries are created under HKEY_LOCAL_MACHINE.
All VSTO Add-ins that you create by using Visual Studio can be registered for the current user. However, VSTO Add-ins can be registered for all users only in certain scenarios. These scenarios depend on the version of Microsoft Office on the computer and how the VSTO Add-in was deployed.
Deployment type
If you use ClickOnce to deploy a VSTO Add-in, the VSTO Add-in can be registered only for the current user. This is because ClickOnce only supports creating keys under HKEY_CURRENT_USER. If you want to register a VSTO Add-in to all users on a computer, you must use Windows Installer to deploy the VSTO Add-in. For more information about these deployment types, see Deploy an Office solution by using ClickOnce and Deploy an Office solution by using Windows Installer.
Registry entries
The required VSTO Add-in registry entries are located under the following registry keys where Root is HKEY_CURRENT_USER or HKEY_LOCAL_MACHINE depending if the installation is for the current user or all users.
| Office Application | Configuration Path |
|---|---|
| Visio | Root\Software\Microsoft\Visio\Addins\add-in ID |
| All Other | Root\Software\Microsoft\Office\Office application name\Addins\add-in ID |
Note
If the installer is targeting all users on 64-bit Windows, it is recommended that it includes two registry entries, one under the HKEY_LOCAL_MACHINE\Software\Microsoft and one under the HKEY_LOCAL_MACHINE\Software\WOW6432Node\Microsoft hive. This is because it's possible for users to use either 32-bit or 64-bit versions of Office on the computer.
If the Installer is targeting the current user, it doesn't need to install to the WOW6432Node because the HKEY_CURRENT_USER\Software path is shared.
For more information, see 32-bit and 64-bit Application Data in the Registry.
The following table lists the entries under this registry key.
| Entry | Type | Value |
|---|---|---|
| Description | REG_SZ | Required. A brief description of the VSTO Add-in. This description is displayed when the user selects the VSTO Add-in in the Add-Ins pane of the Options dialog box in the Microsoft Office application. |
| FriendlyName | REG_SZ | Required. A descriptive name of the VSTO Add-in that is displayed in the COM Add-Ins dialog box in the Microsoft Office application. The default value is the VSTO Add-in ID. |
| LoadBehavior | REG_DWORD | Required. A value that specifies when the application attempts to load the VSTO Add-in and the current state of the VSTO Add-in (loaded or unloaded). By default, this entry is set to 3, which specifies that the VSTO Add-in is loaded at startup. For more information, see LoadBehavior values. Note: If a user disables the VSTO Add-in, that action modifies LoadBehavior value in the HKEY_CURRENT_USER registry hive. For each user, the value of the LoadBehavior value in the HKEY_CURRENT_USER hive overrides the default LoadBehavior defined in the HKEY_LOCAL_MACHINE hive. |
| Manifest | REG_SZ | Required. The full path of the deployment manifest for the VSTO Add-in. The path can be a location on the local computer, a network share (UNC), or a Web server (HTTP). If you use Windows Installer to deploy the solution, you must add the prefix file:/// to the manifest path. You must also append the string |vstolocal (that is, the pipe character | followed by vstolocal) to the end of this path. This ensures that your solution is loaded from the installation folder, rather than the ClickOnce cache. For more information, see Deploy an Office solution by using Windows Installer. Note: When you build a VSTO Add-in on the development computer, Visual Studio automatically appends the |vstolocal string to this registry entry. |
Registry entries for Outlook form regions
If you create a custom form region in a VSTO Add-in for Outlook, additional registry entries are used to register the form region with Outlook. These entries are created under a different registry key for each message class that the form region supports. These registry keys are in the following location, where Root is HKEY_CURRENT_USER or HKEY_LOCAL_MACHINE.
Root\Software\Microsoft\Office\Outlook\FormRegions\message class
Like the other registry entries shared by all VSTO Add-ins, Visual Studio creates the form region registry entries on the development computer when you build your project. Using ClickOnce to deploy your VSTO Add-in, the registry entries are automatically created on the end-user computer. When you use Windows Installer to deploy your VSTO Add-in, you must configure the InstallShield Limited Edition project to create the registry entries on the end-user computer.
For more information about the form region registry entries, see Specify the location of a form region in a custom form. For more information about Outlook form regions, see Create Outlook form regions.
LoadBehavior values
The LoadBehavior entry under the Root\Software\Microsoft\Office\application name\Addins\add-in ID key contains a bitwise combination of values that specify the run time behavior of the VSTO Add-in. The lowest order bit (values 0 and 1) indicates whether the VSTO Add-in is currently unloaded or loaded. Other bits indicate when the application attempts to load the VSTO Add-in.
Typically, the LoadBehavior entry is intended to be set to 0, 3, or 16 (in decimal) when the VSTO Add-in is installed on end-user computers. By default, Visual Studio sets the LoadBehavior entry of your VSTO Add-in to 3 when you build or publish it.
The following table lists all the possible values of the LoadBehavior entry. Some descriptions in this table refer to loading a VSTO Add-in manually or programmatically. To load a VSTO Add-in manually, select the check box next to the VSTO Add-in in the COM Add-Ins dialog box in the application. To load a VSTO Add-in programmatically, set the Connect property of the COMAddIn object that represents the VSTO Add-in to true.
| Value (in decimal) | VSTO Add-in status | VSTO Add-in load behavior | Description |
|---|---|---|---|
| 0 | Unloaded | Don't load automatically | The application never tries to load the VSTO Add-in automatically. The user can try to manually load the VSTO Add-in, or the VSTO Add-in can be loaded programmatically. If the VSTO Add-in is successfully loaded, the LoadBehavior value remains 0, but the status of the VSTO Add-in in the COM Add-ins dialog box is updated to indicate that the VSTO Add-in is loaded. |
| 1 | Loaded | Don't load automatically | The application never tries to load the VSTO Add-in automatically. The user can try to manually load the VSTO Add-in, or the VSTO Add-in can be loaded programmatically. Although the COM Add-ins dialog box indicates that the VSTO Add-in is loaded after the application starts, the VSTO Add-in isn't loaded until it's loaded manually or programmatically. If the application successfully loads the VSTO Add-in, the LoadBehavior value changes to 0, and remains at 0 after the application closes. |
| 2 | Unloaded | Load at startup | The application doesn't try to load the VSTO Add-in automatically. The user can try to manually load the VSTO Add-in, or the VSTO Add-in can be loaded programmatically. If the application successfully loads the VSTO Add-in, the LoadBehavior value changes to 3, and remains at 3 after the application closes. |
| 3 | Loaded | Load at startup | The application tries to load the VSTO Add-in when the application starts. This is the default value when you build or publish a VSTO Add-in in Visual Studio. If the application successfully loads the VSTO Add-in, the LoadBehavior value remains 3. If an error occurs when loading the VSTO Add-in, the LoadBehavior value changes to 2, and remains at 2 after the application closes. |
| 8 | Unloaded | Load on demand | The application doesn't try to load the VSTO Add-in automatically. The user can try to manually load the VSTO Add-in, or the VSTO Add-in can be loaded programmatically. If the application successfully loads the VSTO Add-in, the LoadBehavior value changes to 9. |
| 9 | Loaded | Load on demand | The VSTO Add-in will be loaded only when the application requires it. Such as when a user selects a UI element that uses functionality in the VSTO Add-in (for example, a custom button in the Ribbon). If the application successfully loads the VSTO Add-in, the LoadBehavior value remains 9, but the status of the VSTO Add-in in the COM Add-ins dialog box is updated to indicate that the VSTO Add-in is currently loaded. If an error occurs when loading the VSTO Add-in, the LoadBehavior value changes to 8. |
| 16 | Loaded | Load first time, then load on demand | Set this value if you want your VSTO Add-in to be loaded on demand. The application loads the VSTO Add-in when the user runs the application for the first time. The next time the user runs the application, the application loads any UI elements that are defined by the VSTO Add-in. However, the VSTO Add-in isn't loaded until the user selects a UI element that is associated with the VSTO Add-in. When the application successfully loads the VSTO Add-in for the first time, the LoadBehavior value remains 16 while the VSTO Add-in is loaded. After the application closes, the LoadBehavior value changes to 9. |