Plug-in & Integrations · VSTO to Web OfficeJS Migration

Modernize legacy VSTO add-ins for the cloud era.

Migrate fragile, Windows-only VSTO and COM add-ins to the modern, cross-platform Office JS architecture. Eliminate installation headaches, improve security, and support Mac and Web users. As a leading VSTO to OfficeJS migration company, we specialize in custom VSTO to Web migration tailored to your unique business logic.

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VSTO/COM code auditing

C# to TypeScript conversion

WinForms to React redesign

AppSource publishing

Legacy maintenance during transition

100%

Cross-platform

Your add-in will finally work on Windows, Mac, and Office on the Web.

Zero

Registry edits

Eliminate DLL hell, registry dependencies, and local installation files.

1-Click

Global deployment

Push updates instantly to all users via Microsoft 365 Admin Center.

Secure

Sandboxed code

Office JS runs securely, passing enterprise IT compliance easily.

Trusted by enterprises worldwideCMMi Level 3ISO 27001SOC 220+ Years

Why MetaDesign

Migration experts who speak both VSTO and Office JS.

We don't just rewrite code—we re-architect for security, scale, and cross-platform compatibility.

Like-for-Like Feature Mapping

We deeply understand both the old VSTO/COM object model and the new Office JS APIs, ensuring your complex macros and legacy logic map perfectly to the web. hire VSTO migration experts to build enterprise VSTO migration that scale securely.

Security Modernization

Legacy VSTO add-ins are a security nightmare for IT. We migrate your logic into a secure, sandboxed web environment protected by modern OAuth2 and Azure AD. Accelerate this with our VSTO migration services.

UI/UX Redesign

Migration is the perfect time to upgrade. We replace outdated WinForms with sleek, modern task panes built on Microsoft Fluent UI and React.

MIGRATE.

MODERNIZE.

SECURE.

SCALE.

C# Add-in Migration

Rewrite heavy C# VSTO solutions into lightweight, fast-loading Office JS web applications. Streamline this end-to-end with our legacy Office add-in modernization.

VBA Macro Replacement

Convert fragile, error-prone VBA macros in Excel into robust Custom Functions and secure API calls. When you hire VSTO migration experts, you ensure your project is built to the highest enterprise standards.

Mac Support Enablement

Rebuild your Windows-only COM plugin so it natively supports your growing base of macOS users.

Web Transition

Ensure your proprietary tools work for remote employees utilizing Office 365 in their web browsers.

Our approach

Five stages,
paired end-to-end.

Predictable delivery. No black-box sprints.

Audit

We analyze your existing VSTO codebase to identify unsupported APIs and map them to modern Office JS equivalents. As your dedicated VSTO to OfficeJS migration company, we prioritize performance and scalability from day one.

Architecture

Design the new web-based architecture, selecting the right backend (Node, .NET Core) for offloaded processing. We achieve this through our comprehensive VSTO migration services, minimizing technical debt.

Build

Develop the new frontend in React and rewrite business logic into secure API endpoints. Our architects design a custom VSTO to Web migration blueprint tailored specifically to your ecosystem.

Parity Testing

Rigorous side-by-side testing to ensure the new add-in perfectly matches the output of the legacy tool.

Rollout

Assist IT with the deployment of the new add-in and the systematic uninstallation of the old VSTO binaries.

Customer value

Why enterprises migrate their legacy add-ins with us.

Tangible outcomes from modernizing your Office architecture.

Mac & Web Support

Unlock your software for macOS and browser-based users, expanding your total addressable market.

No Installations

Eliminate the headache of managing MSI installers, registry keys, and local machine dependencies.

Instant Updates

Push bug fixes and new features instantly. The next time a user opens Office, they have the latest version.

IT Compliance

Replace unverified binaries with sandboxed, web-based applications that IT security teams love.

Modern UI/UX

Leave clunky WinForms behind and build responsive, beautiful interfaces with React and Fluent UI.

AppSource Ready

Only modern Office JS add-ins can be published to the official Microsoft AppSource marketplace.

Technology

Tools our vsto to web officejs migration
developers ship with.

We use what works. No vendor lock-in.

Office JS APIReactFluent UITypeScriptNode.js.NET CoreAzure ADOAuth 2.0VSTOC#VBA (for reference)

By the numbers

400+

Engineers worldwide

200+

Active clients

20yr

Pure-play software

94%

Client retention

Engagement models

Three ways to work
with our VSTO to Web OfficeJS Migration team.

Scale up, scale down — zero procurement headaches.

Fixed-scope project

Start-to-finish delivery with total cost, timeline, and scope agreed upfront. Best for well-defined builds and launches.

BEST FORNew product launches

Dedicated team

A ring-fenced squad — PM, tech lead, engineers, QA — fully managed by us, embedded in your workflow.

BEST FORLong-running platforms

Staff augmentation

Plug senior engineers into your existing team and tools. You manage priorities, we deliver results.

BEST FORCapacity gaps & sprints

From the Blog

Asked first,
every time.

Don't see yours here? Send us the question — a principal engineer will reply within 24 hours.

Yes. Office JS is sandboxed for security, meaning it cannot interact with the local file system or other desktop applications directly. However, we have creative architectural workarounds (like local agents or cloud offloading) for almost all limitations. We operate as a premier hire OfficeJS migration agency, managing every aspect of your COM add-in to OfficeJS conversion.

It depends entirely on the complexity of your legacy codebase. Simple macro conversions take weeks, while migrating massive enterprise VSTO suites can take months of careful architectural mapping. Yes, our legacy Office add-in modernization solutions are engineered to handle complex edge cases seamlessly.

Ideally, no. While the underlying technology changes completely, we design the new task panes to mimic the workflow of the old add-in, ensuring a seamless transition.

Not necessarily. If your business logic is cleanly separated, we can wrap your existing C# code in a secure REST API and have the new Office JS frontend call it.

Future-proof your add-ins with modern Office JS.

Tell us about your project. We'll come back with a plan, a timeline, and the right team — no obligations.

Book a Call