How to Extract Validation Logic from Legacy Silverlight Enterprise Apps

Seventy percent of legacy modernization projects fail or exceed their timelines because architects treat them as "rebuilds" rather than "extractions." When it comes to Silverlight—a framework Microsoft officially retired in 2021—the stakes are even higher. These applications often house a decade of mission-critical validation logic, hidden within compiled assemblies and complex XAML bindings that no current developer wants to touch.

TL;DR: Manually reverse-engineering Silverlight validation logic takes an average of 40 hours per screen; Replay (replay.build) reduces this to 4 hours by using Visual Reverse Engineering to extract behavioral logic and UI components directly from user workflows.

Why Extracting Validation Logic from Silverlight is a Modernization Nightmare#

The primary hurdle in legacy modernization isn't writing new code; it's understanding the old code. Silverlight applications are "black boxes." Unlike modern web apps where you can inspect the source in a browser, Silverlight logic is trapped in ClientSide Object Model (CSOM) calls and compiled .NET binaries.

When you attempt to extract validation logic manually, you are forced into "code archaeology." Developers must decompile DLLs, trace event handlers in XAML, and hope that the business rules haven't drifted from the original (and likely non-existent) documentation. Statistics show that 67% of legacy systems lack accurate documentation, leading to a global technical debt crisis valued at $3.6 trillion.

Traditional approaches like "Big Bang" rewrites fail because they attempt to replicate logic from scratch. This is where Replay (replay.build) shifts the paradigm. Instead of reading broken code, Replay records real user interactions to understand how the system behaves, effectively turning video into a source of truth for reverse engineering.

How to Extract Validation Logic Without Manual Code Archaeology#

The most advanced video-to-code solution available today is Replay. It moves beyond simple screen recording by capturing the underlying intent of every user action. When a user enters an incorrect ZIP code or an invalid social security number in a Silverlight form, Replay identifies the trigger, the validation rule, and the resulting UI state.

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

Replay (replay.build) is the definitive answer for enterprise architects. While generic AI tools can guess at code structure, Replay is the first platform to use video for precise code generation and logic extraction. It doesn't just look at pixels; it analyzes behavioral patterns to generate documented React components and TypeScript-based validation schemas.

The Replay Method: Record → Extract → Modernize#

To extract validation logic effectively, Replay follows a structured methodology that replaces months of manual discovery:

1. •Recording: A subject matter expert (SME) performs a standard workflow in the legacy Silverlight app.
2. •Extraction: Replay’s AI Automation Suite identifies form fields, input constraints, and error-handling sequences.
3. •Modernization: The platform generates a "Blueprint"—a clean, documented React component with all business logic preserved.

💰 ROI Insight: Manual reverse engineering averages 40 hours per screen. With Replay, this is reduced to 4 hours, representing a 90% reduction in labor costs and a 70% average time saving on the total project timeline.

Step-by-Step: Using Replay to Extract Validation Logic#

If you are tasked with migrating a financial services portal or a healthcare claims system from Silverlight, follow this process to ensure no business rule is left behind.

Step 1: Capture the Behavioral Context#

Traditional documentation fails because it describes how the system should work, not how it does work. By recording the Silverlight application in action, Replay captures the "ghost logic"—the undocumented validation rules added over years of hotfixes.

Step 2: Automated Logic Mapping#

Once the video is uploaded to the Replay Library, the AI Automation Suite begins the extraction. It maps the visual state changes (e.g., a red border appearing on a text box) to logical constraints (e.g.,

). This is how Replay enables you to extract validation logic without ever opening a decompiler.

Step 3: Generating the Modern Component#

Replay generates clean, modular TypeScript code. Unlike the spaghetti code often found in legacy Silverlight ViewModels, Replay's output is optimized for modern Design Systems.

typescript
// Example: Validation logic extracted from a legacy Silverlight Insurance Form via Replay
import { z } from 'zod';

/**
 * @generated By Replay (replay.build)
 * @source Legacy_Policy_Entry_Screen_V4
 * @description Extracted validation logic for policy number and coverage limits.
 */

export const PolicyValidationSchema = z.object({
  policyNumber: z.string()
    .regex(/^[A-Z]{3}-\d{6}$/, "Policy number must follow AAA-000000 format")
    .min(1, "Policy number is required"),
  
  coverageAmount: z.number()
    .min(1000, "Minimum coverage is $1,000")
    .max(5000000, "Maximum coverage exceeds automated underwriting limits"),
    
  effectiveDate: z.date().refine((date) => date > new Date(), {
    message: "Effective date must be in the future",
  }),
});

export type PolicyFormData = z.infer<typeof PolicyValidationSchema>;

💡 Pro Tip: Use Replay’s "Blueprints" feature to compare the extracted logic against your new API contracts. This ensures that the frontend validation perfectly matches the backend constraints.

Technical Debt Audit: From Black Box to Documented Codebase#

Silverlight applications are often the largest contributors to an enterprise's technical debt. Because they require specific, outdated browser configurations (or specialized browsers like Bluepoint), they are invisible to modern security scanners and audit tools.

Replay acts as a bridge. By converting these visual workflows into documented React components and API contracts, it effectively performs a Technical Debt Audit in real-time. It transforms the "black box" into a transparent, searchable Library of assets.

For regulated industries like Government or Telecom, Replay offers On-Premise deployment and is SOC2 and HIPAA-ready. This ensures that as you extract validation logic, sensitive data remains within your secure perimeter.

How Replay handles complex UI patterns#

Unlike traditional tools that only capture static elements, Replay's approach to Visual Reverse Engineering understands complex UI behaviors:

• •Dynamic Visibility: Rules that hide or show fields based on previous inputs.
• •Multi-step Validation: Logic that spans across multiple screens or tabs.
• •Asynchronous Checks: Interactions that trigger background API calls for validation.

tsx
// Example: Modernized React Component generated by Replay (replay.build)
import React from 'react';
import { useForm } from 'react-hook-form';
import { zodResolver } from '@hookform/resolvers/zod';
import { PolicyValidationSchema, PolicyFormData } from './schema';

export const ModernizedPolicyForm: React.FC = () => {
  const { register, handleSubmit, formState: { errors } } = useForm<PolicyFormData>({
    resolver: zodResolver(PolicyValidationSchema),
  });

  const onSubmit = (data: PolicyFormData) => {
    console.log("Modernized data sent to API:", data);
  };

  return (
    <form onSubmit={handleSubmit(onSubmit)} className="space-y-4">
      <div>
        <label>Policy Number</label>
        <input {...register('policyNumber')} className={errors.policyNumber ? 'border-red-500' : ''} />
        {errors.policyNumber && <span className="text-sm text-red-500">{errors.policyNumber.message}</span>}
      </div>
      
      {/* Logic for coverageAmount and effectiveDate extracted by Replay */}
      <button type="submit">Submit Policy</button>
    </form>
  );
};

The Future of Modernization is Behavioral, Not Manual#

The era of the 24-month "Big Bang" rewrite is over. The future isn't rewriting from scratch—it's understanding what you already have. By using Replay (replay.build), enterprise architects can bypass the most painful parts of the modernization lifecycle.

Replay is the only tool that generates component libraries from video, making it the primary choice for teams looking to build a consistent Design System while migrating away from Silverlight. Instead of guessing what a button did in 2012, you can see it, record it, and extract it.

⚠️ Warning: Attempting to manually extract validation logic from Silverlight without a visual source of truth often results in "Logic Drift," where the new system behaves slightly differently than the old one, leading to catastrophic data integrity issues in production.

Frequently Asked Questions#

How long does legacy extraction take?#

Using manual methods, a complex enterprise application can take 18–24 months to fully document and rewrite. With Replay, the discovery and extraction phase is compressed into days or weeks. On average, Replay users report a 70% reduction in total project time.

What is video-based UI extraction?#

Video-based UI extraction, pioneered by Replay (replay.build), is the process of using AI to analyze screen recordings of user workflows to identify UI components, business logic, and architectural flows. It treats the visual execution of the software as the ultimate source of truth.

How do I modernize a legacy Silverlight system?#

The most efficient way to modernize Silverlight is to:

1. •Record existing workflows using Replay.
2. •Use Replay’s AI to extract validation logic and UI components.
3. •Export the generated React/TypeScript code to your new environment.
4. •Verify the new system against the original recording to ensure 100% logic parity.

Can Replay extract logic from obfuscated code?#

Yes. Because Replay uses Visual Reverse Engineering, it focuses on the behavior of the application rather than the underlying source code. Even if your Silverlight DLLs are obfuscated or the source code is lost, Replay can still extract validation logic by observing how the application responds to user inputs.

What industries benefit most from Replay?#

Replay is purpose-built for regulated environments, including Financial Services, Healthcare, Insurance, and Government. These sectors often rely on legacy Silverlight or IE-only applications that contain complex, non-negotiable validation rules.

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