Silverlight to React Modernization Without Source Code: The Architect’s Guide

Your mission-critical Silverlight application is a black box. The original .NET source code is lost to a decade of developer turnover, the proprietary XAML files are inaccessible, and the browser plugin that once powered your entire enterprise operations is a security liability. For most Enterprise Architects, this is the "Point of No Return"—the moment where a complete, multi-million dollar manual rewrite seems like the only option.

Industry experts recommend moving away from plugin-based architectures immediately, yet 67% of legacy systems lack the documentation required to even begin a migration. When you are forced to perform a silverlight react modernization without access to the original .NET source, you aren't just migrating code; you are performing digital archaeology.

TL;DR: Modernizing Silverlight to React without source code is now possible through Visual Reverse Engineering. By recording user workflows, Replay extracts design tokens, component hierarchies, and business logic flows directly from the UI. This methodology reduces the average modernization timeline from 18 months to a matter of weeks, offering a 70% time savings over manual reconstruction.

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The $3.6 Trillion Technical Debt Crisis#

The global technical debt has ballooned to $3.6 trillion, and Silverlight applications represent a significant, high-risk portion of that debt. Because Silverlight was a compiled, client-side technology, the "logic" is often trapped inside

files that are difficult to decompile into meaningful, modern C#.

According to Replay’s analysis, the primary blocker for enterprise migration isn't the target language (React), but the "Documentation Gap." When the source code is missing or obfuscated, functional requirements must be manually rediscovered by interviewing end-users and observing legacy screens.

Video-to-code is the process of using computer vision and AI to record these legacy interactions and transform them into structured, documented React components and design systems. This bypasses the need for the original .NET source entirely.

Why Traditional Rewrites Fail (and Why You Can't Wait)#

Statistics show that 70% of legacy rewrites fail or exceed their original timeline. The "Big Bang" rewrite—where a team tries to replicate 10 years of Silverlight features in React from scratch—usually collapses under the weight of "feature creep" and undocumented edge cases.

For organizations in Financial Services or Healthcare, the risk of a failed rewrite is not just financial—it’s operational. If you are attempting a silverlight react modernization without the original XAML or C# files, manual reconstruction is a recipe for catastrophic regression.

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The Methodology: Silverlight React Modernization Without Original Source#

When the source code is gone, the UI becomes your "Source of Truth." This approach relies on capturing the "Intent" of the application rather than the "Implementation" of the legacy code.

1. Visual Capture and Design Token Extraction#

The first step is recording every state of the Silverlight application. Since the application likely runs in an isolated environment (like a specialized IE11 VM or a browser emulator), you record the workflows. Replay's AI analyzes these recordings to identify repeating UI patterns—buttons, data grids, modal windows, and navigation structures.

2. Building the Design System (The Library)#

Before writing a single line of business logic, you must establish a Design System. Replay automatically extracts colors, typography, and spacing from the recorded video to create a modern Tailwind or CSS-in-JS theme.

Design System Extraction is the automated identification of UI primitives from visual data, ensuring the new React application maintains brand consistency without manual CSS mapping.

3. Component Synthesis#

Once the tokens are identified, the platform generates functional React components. Below is an example of how a complex Silverlight DataGrid—often the most difficult element to migrate—is transformed into a clean, typed React component using Replay’s output.

typescript
// Generated React Component from Silverlight Grid Capture
import React from 'react';
import { useTable } from '@/hooks/useTable';
import { Button } from '@/components/ui/button';

interface PolicyData {
  id: string;
  policyNumber: string;
  holderName: string;
  premiumAmount: number;
  expiryDate: string;
}

export const PolicyDashboard: React.FC = () => {
  // Replay identifies data patterns and suggests Type definitions
  const { data, loading } = useTable<PolicyData>('/api/v1/policies');

  return (
    <div className="p-6 bg-slate-50 rounded-xl shadow-sm">
      <h2 className="text-2xl font-bold mb-4">Insurance Policy Overview</h2>
      <table className="min-w-full divide-y divide-gray-200">
        <thead>
          <tr>
            <th>Policy #</th>
            <th>Holder</th>
            <th>Premium</th>
            <th>Status</th>
          </tr>
        </thead>
        <tbody className="bg-white">
          {data.map((policy) => (
            <tr key={policy.id}>
              <td className="px-6 py-4">{policy.policyNumber}</td>
              <td className="px-6 py-4">{policy.holderName}</td>
              <td className="px-6 py-4">${policy.premiumAmount}</td>
              <td>
                <Button variant="outline" onClick={() => handleEdit(policy.id)}>
                  View Details
                </Button>
              </td>
            </tr>
          ))}
        </tbody>
      </table>
    </div>
  );
};

Discover how Replay handles complex component generation

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Technical Deep Dive: Mapping XAML Logic to React Hooks#

In a silverlight react modernization without source code, the biggest challenge is replicating the state management and event handling that was previously buried in C# code-behind files.

Silverlight relied heavily on

and two-way data binding. In a modern React environment, we translate these behaviors into functional state management (useState, useReducer) or global stores like Zustand or Redux.

Reconstructing "Hidden" Logic#

When you record a workflow in Replay, the "Flows" feature maps the sequence of events. If clicking "Submit" on Screen A opens a filtered view on Screen B, Replay documents this transition logic.

Industry experts recommend this "outside-in" approach because it ensures the new system matches the user's mental model, even if the underlying legacy database calls were inefficient or convoluted.

typescript
// Reconstructing Silverlight Event Logic in React
import { useState, useEffect } from 'react';

export const useSilverlightTransition = (initialState: any) => {
  const [state, setState] = useState(initialState);

  // Replay's "Flows" identifies that this logic 
  // was triggered by the 'OnSelectionChanged' event in XAML
  const handleSelectionChange = (newItem: any) => {
    // Logic inferred from visual state changes
    if (newItem.isValid) {
      setState((prev) => ({ ...prev, selectedItem: newItem, viewMode: 'detail' }));
    }
  };

  return { state, handleSelectionChange };
};

Learn more about mapping legacy workflows to React Flows

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Security and Compliance in Regulated Environments#

For industries like Insurance, Government, and Telecom, "Cloud-only" is often not an option. Legacy Silverlight apps often handle sensitive PII (Personally Identifiable Information) or PHI (Protected Health Information).

Replay is built for these high-stakes environments. The platform is SOC2 compliant and HIPAA-ready. More importantly, for organizations with strict data residency requirements, Replay offers an On-Premise deployment option. This allows you to perform your silverlight react modernization without sending sensitive UI recordings to a public cloud.

The "Clean Room" Modernization#

By using visual reverse engineering, you create a "Clean Room" environment. You are not copying old, potentially vulnerable .NET code. Instead, you are generating fresh, secure React code that follows modern security headers, OWASP guidelines, and sanitized data handling practices.

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Scaling the Migration: From One Screen to Thousands#

The average enterprise Silverlight application contains between 50 and 300 unique screens. If a manual developer takes 40 hours per screen to document, design, and code, a 100-screen app requires 4,000 developer hours. At a standard enterprise rate, that is a $600,000 investment for just the UI layer.

Using Replay, that timeline is slashed by 70%.

1. •The Library: Centralize your UI components. Once a "Silverlight DataGrid" is defined in Replay, it is reused across every screen.
2. •The Blueprints: Use the visual editor to tweak the AI-generated code before exporting.
3. •Automated Documentation: Replay generates the documentation that was missing for the last decade, ensuring the next generation of developers won't face the same "Black Box" problem.

According to Replay's analysis, the cost savings of automated documentation alone covers the ROI of the platform within the first six months of a modernization project.

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Frequently Asked Questions#

Can I really perform a silverlight react modernization without any source code?#

Yes. Visual Reverse Engineering uses the rendered UI as the source of truth. By capturing the application's behavior, layout, and data flow through video, Replay can reconstruct the component architecture and design system in React without ever needing to see the original XAML or C# code.

How does Replay handle complex Silverlight controls like DataGrids and Charts?#

Replay’s AI is trained to recognize standard enterprise UI patterns. It identifies the functional boundaries of complex controls (like pagination, sorting, and filtering in a grid) and maps them to modern React equivalents, such as TanStack Table or Recharts, ensuring that the functionality remains identical even if the underlying implementation is completely new.

Is the generated React code maintainable?#

Unlike "transpilers" or "black-box converters" of the past, Replay generates clean, human-readable TypeScript and React code. It follows modern best practices, including component modularity, Tailwind CSS for styling, and standard Hook-based state management. The goal is to provide a foundation that your internal team can own and extend immediately.

What happens to the backend APIs?#

While Replay focuses on the UI and Frontend architecture, it helps bridge the backend gap by identifying the data structures required by the UI. This allows your backend team to build modern REST or GraphQL APIs that match the expected "data contracts" inferred from the legacy Silverlight interactions.

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Conclusion: The Path Forward#

The "Source Code Gap" is no longer a valid excuse for maintaining high-risk Silverlight applications. The cost of inaction—browser incompatibility, security vulnerabilities, and developer scarcity—far outweighs the effort of a modern, visual-first migration.

By leveraging Replay, Enterprise Architects can turn a 24-month nightmare into a 24-day win. You can deliver a high-performance, SOC2-compliant React application that looks and feels exactly like the original, but runs on a modern, scalable stack.

Ready to modernize without rewriting? Book a pilot with Replay