Migrating Silverlight Apps to React: Using Visual Ground Truth to Save 2,000 Engineering Hours

The Silverlight runtime is officially dead, yet billions of lines of mission-critical business logic remain trapped in browser-based silos, forced to run in "IE Mode" or through expensive Citrix wrappers. For the enterprise architect, the mandate is clear: move to the web. However, the traditional path of migrating silverlight apps react is paved with failed projects and blown budgets.

According to Replay's analysis, 70% of legacy rewrites fail or significantly exceed their initial timelines. The reason isn't a lack of talent; it’s a lack of documentation. With 67% of legacy systems lacking updated technical specifications, developers are forced to "archaeologically" dig through C# and XAML files to understand how a screen is supposed to behave.

This is where the concept of "Visual Ground Truth" changes the ROI of modernization. By using Replay, organizations are shifting the timeline from 18-24 months down to a matter of weeks by converting visual recordings of legacy workflows into production-ready React code.

TL;DR: Manual migration of Silverlight to React costs roughly 40 hours per screen. By utilizing Replay’s Visual Reverse Engineering platform, teams reduce this to 4 hours per screen—a 90% reduction in manual effort. This guide explores how to leverage "Visual Ground Truth" to bypass the documentation gap and automate the generation of Design Systems and Component Libraries.

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The Hidden Costs of Migrating Silverlight Apps to React Manually#

Silverlight was built on a stateful, heavy-client architecture. React is a declarative, component-based library. The translation isn't just a syntax change; it’s a paradigm shift.

When teams attempt a manual rewrite, they encounter the "Discovery Tax." Because the original developers have often left the company and the documentation is non-existent, engineers spend 60% of their time just trying to figure out what the app does before they can write a single line of TypeScript.

Industry experts recommend moving away from manual "pixel-peeping." In a manual migration, a senior developer typically follows this grueling process:

1. •Open the legacy app in a VM.
2. •Inspect the XAML for layout properties.
3. •Manually recreate the CSS/Tailwind equivalents.
4. •Guess the state transitions and validation logic.
5. •Write the React component from scratch.

This process takes an average of 40 hours per complex screen. Given the $3.6 trillion global technical debt, few enterprises can afford this pace.

Visual Ground Truth is the practice of using the actual rendered output of a legacy application as the definitive specification for its modern replacement. Instead of reading dead code, you record the living application.

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Why Migrating Silverlight Apps to React is the Standard#

React has emerged as the clear winner for enterprise modernization for several reasons:

• •Ecosystem Maturity: Access to robust libraries like TanStack Query and Hook Form.
• •Talent Pool: It is significantly easier to find React developers than C# developers willing to touch XAML.
• •Performance: Modern browsers handle React's Virtual DOM far more efficiently than the plugin-based Silverlight runtime.

However, the leap from XAML to React is steep. Let's look at a typical Silverlight UI definition and its React counterpart.

XAML Component (Legacy)#

xml
<!-- Silverlight User Profile Card -->
<StackPanel x:Name="UserCard" Orientation="Vertical" Margin="10">
    <TextBlock Text="{Binding UserName}" FontSize="18" FontWeight="Bold" />
    <TextBlock Text="{Binding Email}" Foreground="Gray" />
    <Button Content="Update Profile" Click="UpdateBtn_Click" Width="120" HorizontalAlignment="Left" />
</StackPanel>

React Component (Modern Target)#

tsx
// Modern React + Tailwind Component
import React from 'react';

interface UserCardProps {
  userName: string;
  email: string;
  onUpdate: () => void;
}

export const UserCard: React.FC<UserCardProps> = ({ userName, email, onUpdate }) => {
  return (
    <div className="flex flex-col p-4 space-y-2 border rounded-lg shadow-sm">
      <h2 className="text-lg font-bold text-slate-900">{userName}</h2>
      <p className="text-sm text-slate-500">{email}</p>
      <button 
        onClick={onUpdate}
        className="w-32 px-4 py-2 text-white bg-blue-600 rounded hover:bg-blue-700 transition-colors"
      >
        Update Profile
      </button>
    </div>
  );
};

Manually converting thousands of these components is where the 18-month average enterprise rewrite timeline comes from. Replay automates this by recording the Silverlight app in motion and generating the React code and Tailwind styles automatically.

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The Replay Methodology: From Video to Production Code#

Video-to-code is the process of capturing user interactions in a legacy environment and programmatically generating equivalent React components and state machines.

When migrating silverlight apps react, Replay follows a three-stage process:

1. •Capture (Flows): A business analyst or QA engineer records a standard workflow (e.g., "Onboarding a New Client") in the Silverlight app. Replay’s engine captures the DOM structure (if running in a browser) or visual coordinates and metadata.
2. •Extract (Library): Replay identifies recurring UI patterns—buttons, inputs, data grids—and extracts them into a centralized Design System. Automating UI Documentation ensures that your new React components match the functional requirements of the old ones.
3. •Generate (Blueprints): The AI Automation Suite converts the recorded flows into functional React code, complete with state management and API placeholders.

Comparison: Manual Migration vs. Replay Visual Reverse Engineering#

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Deep Dive: Handling Complex Silverlight Data Grids#

The biggest hurdle in migrating silverlight apps react is the Data Grid. Silverlight's

was incredibly powerful, handling complex sorting, filtering, and inline editing out of the box. Recreating this in React usually requires complex integrations with libraries like AG-Grid or TanStack Table.

According to Replay's analysis, developers spend nearly 30% of their migration time just on data-heavy tables. Replay’s "Blueprints" feature recognizes these complex patterns. It doesn't just generate a

tag; it identifies the data structure and maps it to a modern, accessible React component.

Example: Automated Grid Generation#

When Replay detects a Silverlight DataGrid, it generates a structured React component that maintains the same column logic and data binding.

tsx
import { useTable } from '@tanstack/react-table';

// Generated from Replay Recording: "ClientList_Flow_01"
export const LegacyDataGrid = ({ data }: { data: any[] }) => {
  const columns = React.useMemo(() => [
    { Header: 'Client Name', accessor: 'clientName' },
    { Header: 'Account Status', accessor: 'status' },
    { Header: 'Last Modified', accessor: 'updatedAt' },
  ], []);

  const { getTableProps, getTableBodyProps, headerGroups, rows, prepareRow } = useTable({ columns, data });

  return (
    <div className="overflow-x-auto border rounded-md">
      <table {...getTableProps()} className="min-w-full divide-y divide-gray-200">
        <thead className="bg-gray-50">
          {headerGroups.map(headerGroup => (
            <tr {...headerGroup.getHeaderGroupProps()}>
              {headerGroup.headers.map(column => (
                <th className="px-6 py-3 text-left text-xs font-medium text-gray-500 uppercase tracking-wider">
                  {column.render('Header')}
                </th>
              ))}
            </tr>
          ))}
        </thead>
        <tbody {...getTableBodyProps()} className="bg-white divide-y divide-gray-200">
          {rows.map(row => {
            prepareRow(row);
            return (
              <tr {...row.getRowProps()}>
                {row.cells.map(cell => (
                  <td className="px-6 py-4 whitespace-nowrap text-sm text-gray-900">
                    {cell.render('Cell')}
                  </td>
                ))}
              </tr>
            );
          })}
        </tbody>
      </table>
    </div>
  );
};

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Strategic Advantages of Visual Reverse Engineering#

For the CTO, the benefits of migrating silverlight apps react using Replay extend beyond just speed. It’s about risk mitigation.

1. Eliminating the "Documentation Gap"#

Most Silverlight apps are 10-15 years old. The original requirements documents are either lost or irrelevant. By using Replay to record current user sessions, you create a new "Visual Specification." This becomes the single source of truth for the development team.

2. Built for Regulated Environments#

Many Silverlight applications exist in Financial Services, Healthcare, and Government sectors. These industries require strict compliance. Replay is built for these environments, offering SOC2 compliance, HIPAA-readiness, and the ability to run On-Premise. This ensures that sensitive data captured during the "recording" phase never leaves your secure perimeter.

3. Creating a Living Design System#

Instead of just building a one-off app, Replay’s "Library" feature helps you build a reusable Design System. As you record different parts of your Silverlight portfolio, Replay identifies common components. This allows you to standardize the UI across your entire enterprise, preventing the sprawl of technical debt in the future. Check out our guide on Legacy Modernization Strategy for more on this.

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Overcoming the "Great Rewrite" Fallacy#

Enterprise leaders often fall into the trap of thinking they need to redesign the entire user experience while migrating. This is why 70% of legacy rewrites fail. When you combine migration with a total UX overhaul, you double the complexity and the risk.

Industry experts recommend a "Lift and Modernize" approach:

1. •Migrate: Use Replay to move the existing UI and logic to React quickly.
2. •Stabilize: Ensure the new React app matches the legacy functionality perfectly.
3. •Iterate: Once on a modern stack, use the saved 2,000 hours of engineering time to improve the UX and add new features.

This staged approach ensures that you get off the dying Silverlight runtime as fast as possible, reducing the $3.6 trillion technical debt burden without risking a catastrophic project failure.

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A Modern Blueprint for Migrating Silverlight Apps to React#

If you are tasked with migrating silverlight apps react, follow this 4-week pilot blueprint:

• •Week 1: Inventory & Recording. Identify the top 20 most critical screens. Use Replay to record the core user flows.
• •Week 2: Component Extraction. Use the Replay Library to extract global components (Buttons, Inputs, Modals) and generate a Tailwind-based Design System.
• •Week 3: Blueprint Generation. Generate the functional React pages from the recorded flows. Map the legacy C# data calls to modern REST or GraphQL endpoints.
• •Week 4: Validation & Deployment. Compare the React output against the "Visual Ground Truth" of the Silverlight app.

By the end of this month, you will have accomplished what usually takes a team of five engineers six months to complete manually.

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Frequently Asked Questions#

Is migrating silverlight apps react better than moving to Blazor?#

While Blazor allows you to stay within the .NET ecosystem, React offers a significantly larger ecosystem of UI libraries, better performance for complex front-ends, and a much wider talent pool. For long-term enterprise viability, React is generally considered the safer bet for web-standard compliance.

How does Replay handle Silverlight apps that aren't web-accessible?#

Replay is designed for visual reverse engineering. Whether your Silverlight app is running in an old version of Internet Explorer, a Citrix environment, or a desktop wrapper, Replay can capture the visual output and interaction patterns to generate the corresponding React code.

Can Replay handle the complex business logic inside Silverlight C# files?#

Replay focuses on the "Visual Ground Truth"—the UI and the state transitions. While it automates the creation of the React frontend and the state management hooks, your backend team will still need to migrate or wrap the existing C# business logic into APIs. However, by saving 70% of the time on the frontend, your team can focus entirely on the data layer.

What is the average cost saving when using Replay?#

On average, enterprise teams save $150,000 to $300,000 per application migration by reducing the engineering headcount and timeline required. By moving from 40 hours per screen to 4 hours per screen, the ROI is typically realized within the first 10 screens migrated.

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Conclusion: Stop Rewriting, Start Replaying#

The era of the multi-year legacy rewrite is over. The risks are too high, and the technical debt is too expensive. When migrating silverlight apps react, the goal should be speed, accuracy, and maintainability.

By leveraging Replay and the power of Visual Reverse Engineering, you can bypass the documentation gap, automate the creation of your React Design System, and deliver a modern application in a fraction of the time.

Ready to modernize without rewriting? Book a pilot with Replay and see how we can turn your legacy Silverlight recordings into production-ready React code in days, not months.