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Visual Studio Tools for Office (VSTO) is a set of development tools available in the form of aVisual Studio add-in (project templates) and aruntime that allowsMicrosoft Office2003 and later versions of Office applications to host the.NET FrameworkCommon Language Runtime (CLR) to expose their functionality via .NET.

This allows extensions to the Office applications to be written inCLI compliant languages as well as to use functionality and user interface constructs from Office applications in .NET applications.^[1] Extensions to Office prior to Office 2003 only allowed the creation ofCOM add-ins usingVisual Basic orVisual C++ and a "Developer" edition was also offered that enabledVBA developers to create COM Add-ins.

VSTO supersedes developer editions of Office 2000 and Office XP for Office development. The developer editions of Office have been discontinued after Office XP and VSTO is available for Office 2003 and later versions only. The VSTO runtime, although part of VSTO development tools, is also downloadable separately if required. COM addin development is still possible for Office 2000 and all later versions using theShared Add-in template in any version ofMicrosoft Visual Studio.

The VSTO add-ins (project types and controls) are also developed using Visual Studio. For Visual Studio .NET 2003 and Visual Studio 2005, it was available only as a standalone edition with support for .NET languages limited to Visual Basic.NET and C#. It was also included as a part of theVisual Studio Team System 2005.

Later on, the Visual Studio Tools for Office 2005 Second Edition (VSTO 2005 SE) was released as a free add-in to Visual Studio Professional and above that includes Office 2007 and 2003 support. However, for Visual Studio Professional Edition, it installs only the application-level add-ins; it does not add the document-level customizations or other functionality (actions pane, host controls, visual document designer, etc.) available in the full version of VSTO or Team System editions.^[2][3]

The current version is Visual Studio Tools for Office 2012 (VSTO 4.5) which is compatible with Office 2016, Office 2013, Office 2010, and Office 2007.

Like VBA, code written for VSTO is executed by a separatevirtual machine (the CLR) which is hosted inside the Microsoft Office applications. However, unlike VBA, where the code isstored in the document file itself, programs written with VSTO are stored in separateCLI assemblies which are associated with the documents by means of custom properties.^[4]

If the properties are present, Microsoft Office hosts the CLR and loads the assembly specified in the property into a separateappdomain named after the document's name.^[5] VSTO applications are subject to the .NET FrameworkCode Access Security constraints, in addition to thedigital signature based permission model that governs VBA macros.^[6]

VSTO development is normally performed using Visual Studio as used by professional programmers. The Office application is (re)started for each debugging session. VBA is normally developed from within the Office application and requires no special tools. VBA also has a macro recorder that can generate VBA code from user actions which is useful for non-professional programmers.

Office extensions or add-ins can be developed using VSTO and JavaScript API technologies. VSTO is Microsoft .NET technology and add-ins using JavaScript API technology use JavaScript, HTML and CSS.

JavaScript API add-ins are highly portable across platforms like iOS, mobile phones, tablets and Windows. The complete licensing process and cycle is easy and maintained within add-ins. Interactive visualization is feasible in JavaScript API add-ins using Charts, ClipArt and Maps.

JavaScript API add-in development is comparatively new technology and is introduced with Office 2016. There are limited APIs and functions available and supported.

VSTO has complete access to all Office object models. It is feasible to perform all operations on the Office client. Features that requires accessing local machine file systems and other applications are feasible and easy in VSTO. C# or any otherCLI programming language can be used to create new Office add-ins.

The latest version of VSTO, as of 2018, is "Office Tools for Visual Studio" and is available with all versions of Microsoft Visual Studio 2017.

VSTO 2003, 2005, 3.0 and 2010 runtimes install in side-by-side (SxS) mode. VSTO 2005 SE runtime replaces the earlier VSTO 2005 runtime. VSTO 2010 runtime installs side-by-side with VSTO 3.0, however, Office 2007 applications can also use the VSTO 2010 runtime. All older VSTO solutions will continue to run in newer versions of Office as long as the runtime against which they were developed is installed.

VSTO solutions developed against newer Office versions will not work in older Office versions as they lack the necessary Primary Interop Assemblies (PIAs)^[7] Office 2010 applications will always use VSTO 2010 Runtime. Design-time support is as follows:

Code developed with various editions of VSTO will only work with certain releases and editions of Microsoft Office 2003 and related products. Specifically, VSTO solutions developed in editions prior to VSTO 2005 SE will not work with any edition of Office 2003 other than Professional. VSTO solutions developed with VSTO 2005 SE will work with Office 2003 Standard (only application-level add-ins) and Professional. VSTO 2005 SE solutions will work with all editions of Office 2007.

• Microsoft Visual Studio
• Visual Studio Tools for Applications (VSTA)

• Visual Studio Tools for Office homepage
• VSTO 2.0 SE (VS 2005) Add-in (Office 2003 and Office 2007)
• VSTO 2.0 SE (VS 2005) Runtime for Office 2003 and Office 2007
• VSTO 3.0 (VS 2008) Runtime for Office 2007
• VSTO 4.0 (VS 2010/2012/2013) Runtime for Office 2007/2010/2013 (permalink)
• Jake Ginnivan: Adding Value to Software projects with VSTOArchived 2014-12-17 at theWayback Machine

• Microsoft Visual Studio

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