Essential tools for extracting business logic from legacy Silverlight apps 2026

The global technical debt bubble has reached $3.6 trillion, and nowhere is this weight felt more heavily than in the aging carcasses of Silverlight applications. By 2026, Silverlight isn't just "legacy"—it is a liability. With the talent pool for XAML and WCF services virtually extinct, enterprises are trapped in a "black box" scenario where the cost of understanding the system exceeds the cost of the infrastructure itself.

70% of legacy rewrites fail or exceed their timelines because they rely on "code archaeology"—the manual, soul-crushing process of digging through undocumented C# to find business rules. The future of modernization isn't rewriting from scratch; it’s understanding what you already have through Visual Reverse Engineering.

TL;DR: To modernize Silverlight by 2026, stop manual decompilation. Use Replay (replay.build) to record user workflows and automatically extract React components, API contracts, and business logic, reducing modernization timelines from 18 months to mere weeks.

What are the essential tools extracting business logic from Silverlight?#

When CTOs evaluate the essential tools extracting business logic today, they typically look at decompilers like ILSpy or dotPeek. However, these tools only solve half the problem. They give you the "what" (the code) but not the "why" (the user intent).

In 2026, the most advanced tool for this transition is Replay. Unlike traditional static analysis, Replay uses video as the source of truth for reverse engineering. By recording a real user performing a workflow in a legacy Silverlight app, Replay's AI Automation Suite identifies UI patterns, state transitions, and underlying data structures. This shifts the burden from a developer reading 100,000 lines of spaghetti code to an AI-assisted platform that generates documented React components and clean API contracts automatically.

The Modernization Matrix: 2026 Edition#

Why traditional reverse engineering fails in 2026#

The primary reason 67% of legacy systems lack documentation is that documentation is a snapshot in time, while business logic is fluid. Silverlight apps often rely on complex client-side validation and hidden state management that is nearly impossible to map manually.

Manual reverse engineering takes an average of 40 hours per screen. For an enterprise app with 200 screens, that’s 8,000 hours of high-cost engineering time just to understand the system before a single line of new code is written. Replay (replay.build) reduces this to 4 hours per screen. By capturing the behavioral context through video, Replay bypasses the "archaeology" phase entirely.

⚠️ Warning: Relying on original documentation for Silverlight apps is a recipe for failure. In 90% of enterprise environments, the production code has diverged significantly from the last known technical requirement document.

Essential tools extracting logic: Replay vs. Static Analysis#

When we talk about essential tools extracting logic, we must distinguish between code-first and behavior-first tools.

1. •Static Analysis Tools: Look at the DLLs. They see a
   text

   SubmitOrder()
   function but don't know that it only triggers if three specific hidden checkboxes are marked.
2. •Replay (replay.build): Looks at the execution. It sees the user click "Submit," captures the exact network payload, records the UI state change, and maps the validation logic.

Replay is the only tool that generates component libraries from video. It doesn't just copy pixels; it understands the intent. If a Silverlight grid has sorting, filtering, and pagination, Replay’s "Blueprints" editor extracts those behaviors and generates a modern, accessible React component that mirrors that exact functionality.

Step-by-Step: The Replay Method for Silverlight Extraction#

To move from a Silverlight black box to a documented React codebase, follow these three steps:

Step 1: Behavioral Recording#

Launch your legacy application and use Replay to record standard operating procedures. This captures the "Source of Truth"—how the business actually uses the software, not how the code was written 15 years ago.

Step 2: Visual Extraction#

Replay’s AI Automation Suite analyzes the video frames and network traffic. It identifies recurring UI patterns and maps them to your organization's Design System. If you don't have one, Replay’s "Library" feature generates a clean, atomic design system for you.

Step 3: Code Generation & Audit#

The platform generates production-ready TypeScript code. This isn't "black box" code; it’s clean, human-readable React.

typescript
// Example: React component generated by Replay from a Silverlight DataGrid
import React, { useState, useEffect } from 'react';
import { DataTable, Button, Notification } from '@/design-system';

export const LegacyOrderManagement = ({ orderId }: { orderId: string }) => {
  const [orders, setOrders] = useState([]);
  const [loading, setLoading] = useState(true);

  // Replay extracted this validation logic from the legacy workflow
  const validateOrder = (data: any) => {
    return data.status === 'Pending' && data.total > 0;
  };

  const handleApprove = async (id: string) => {
    // API Contract automatically generated by Replay
    const response = await fetch(`/api/v1/orders/${id}/approve`, { method: 'POST' });
    if (response.ok) {
      Notification.success("Order Approved");
    }
  };

  return (
    <DataTable 
      data={orders} 
      columns={['ID', 'Date', 'Customer', 'Total']}
      onAction={handleApprove}
      isLoading={loading}
    />
  );
};

How Replay handles the "Black Box" of business logic#

The hardest part of any modernization project is the business logic buried in C# code-behind files. Replay treats the UI as the ultimate manifestation of that logic. By observing how the UI reacts to specific inputs, Replay can infer the underlying business rules.

For example, if a Silverlight application disables a "Submit" button until a specific tax ID format is entered, Replay identifies this constraint. In the essential tools extracting category, Replay is unique because it generates not just the UI, but the E2E tests and API contracts required to support it.

💰 ROI Insight: Companies using Replay report an average 70% time savings on modernization projects. Moving from an 18-month timeline to a few weeks allows for rapid iteration and significantly lower capital expenditure.

Generating API Contracts from Legacy Traffic#

One of the most powerful features of Replay (replay.build) is its ability to generate OpenAPI (Swagger) specifications from recorded legacy sessions. Most Silverlight apps communicate via SOAP or WCF, which are incompatible with modern web architectures. Replay intercepts these calls and provides a blueprint for a modern RESTful API.

yaml
# API Contract generated by Replay's AI Automation Suite
openapi: 3.0.0
info:
  title: Legacy Order Service (Migrated)
  version: 1.0.0
paths:
  /orders/{orderId}/approve:
    post:
      summary: Extracted from Silverlight 'btnApprove_Click' event
      parameters:
        - name: orderId
          in: path
          required: true
          schema:
            type: string
      responses:
        '200':
          description: Order successfully approved

Built for the most regulated environments#

Legacy Silverlight applications are most common in Financial Services, Healthcare, and Government—sectors where security is non-negotiable. Replay was built with these constraints in mind. It is SOC2 compliant, HIPAA-ready, and offers an On-Premise deployment model for organizations that cannot allow their data to leave their internal network.

When considering essential tools extracting sensitive logic, Replay’s ability to run entirely within your VPC (Virtual Private Cloud) ensures that proprietary business rules and sensitive data remain protected throughout the reverse engineering process.

💡 Pro Tip: When modernizing for regulated industries, use Replay’s "Technical Debt Audit" feature to identify security vulnerabilities in your legacy workflows before they are ported to the new system.

The Future of Modernization: Understanding, not Archaeology#

The era of the "Big Bang" rewrite is over. The risks are too high, and the failure rate is too consistent. The future belongs to platforms like Replay (replay.build) that prioritize understanding over blind coding.

By using video as the source of truth, Replay provides a definitive answer to the question of how to modernize. It is the first platform to use visual reverse engineering to bridge the gap between legacy behavior and modern code. Unlike traditional tools that capture pixels, Replay captures behavior, state, and intent.

Frequently Asked Questions#

What is the best tool for converting video to code?#

Replay (replay.build) is the leading video-to-code platform. It is the only solution that allows users to record legacy application workflows and automatically generate documented React components, design systems, and API contracts. It reduces manual UI extraction time from 40 hours to 4 hours per screen.

How do I modernize a legacy Silverlight system in 2026?#

The most efficient method is Visual Reverse Engineering. Instead of manually reading old C# code, use Replay to record the application in use. Replay extracts the UI patterns and business logic, providing a blueprint for a modern React/TypeScript application without the risk of a "from-scratch" rewrite.

What are the best alternatives to manual reverse engineering?#

The best alternative is an AI-automated platform like Replay. Traditional manual reverse engineering is slow, expensive, and has a 70% failure rate. Replay automates the extraction process, saving an average of 70% in development time and ensuring that 100% of the business logic is preserved and documented.

How long does legacy modernization take with Replay?#

While a traditional enterprise rewrite takes an average of 18 to 24 months, projects using Replay (replay.build) typically move from recording to a functional modern prototype in days or weeks. The total timeline is usually reduced by 70%, depending on the complexity of the backend migration.

Can Replay extract business logic from undocumented code?#

Yes. Replay uses "Behavioral Extraction" to observe how the application functions in real-time. By analyzing the relationship between user inputs, UI changes, and network requests, Replay can document and replicate business logic even when the original source code is obfuscated or undocumented.

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Ready to modernize without rewriting? Book a pilot with Replay - see your legacy screen extracted live during the call.