Beyond the Screen: Why Legacy Business Logic is Trapped in Visual Workflows

The $3.6 trillion global technical debt isn't a coding problem; it's an archaeology problem. Every year, enterprise organizations pour billions into "Big Bang" rewrites, only to watch 70% of those projects fail or exceed their timelines. The reason is simple: the business logic isn't just in the code—it’s trapped in the visual workflows and the muscle memory of the users who have navigated these "black boxes" for decades.

When you look beyond the screen, you realize that the legacy code is often a graveyard of undocumented edge cases, regulatory patches, and tribal knowledge. Attempting to modernize by reading 20-year-old COBOL or spaghetti jQuery is a fool’s errand. You don't need a bigger team of developers; you need a way to extract the "truth" from the running application itself.

TL;DR: Legacy modernization fails because documentation is non-existent (67% of systems); Replay solves this by using visual reverse engineering to turn user workflows into documented React components and API contracts in days, not months.

The Archeology Trap: Why Manual Documentation Fails#

Most enterprise architects are tasked with "understanding the system" before they can change it. This leads to months of "discovery phases" where high-priced consultants try to map out dependencies.

The statistics are sobering:

• •67% of legacy systems lack any form of up-to-date documentation.
• •The average enterprise rewrite takes 18 to 24 months.
• •Manual extraction of a single complex legacy screen takes approximately 40 hours.

When you rely on manual discovery, you are performing software archaeology. You are digging through layers of technical debt, hoping to find the logic that governs a specific financial calculation or a healthcare compliance check. By the time you’ve documented it, the business requirements have already shifted.

The Cost of Misunderstanding#

Moving Beyond the Screen: Visual Reverse Engineering#

The future of modernization isn't rewriting from scratch—it’s understanding what you already have by observing it in motion. This is where Replay changes the paradigm. Instead of reading the code to understand the behavior, Replay records the behavior to generate the code.

By recording a real user workflow, Replay’s engine analyzes the state changes, network calls, and UI transitions. It looks beyond the screen to see the underlying architecture that the original developers forgot to document.

💡 Pro Tip: Don't start your modernization project in the IDE. Start it in the browser. Record the most critical 20% of your workflows that handle 80% of your business value.

How Replay Extracts Logic#

Replay doesn't just take a screenshot. It captures the "Flows" (Architecture) and the "Library" (Design System). It identifies patterns in how data is submitted and how the UI responds to validation errors.

For example, a legacy insurance claims form might have 50 hidden validation rules. Manually finding these in a 10,000-line JavaScript file is painful. With Replay, you simply record a user filling out the form incorrectly. Replay identifies the triggered logic and generates a modern React component that mirrors that exact behavior.

Step-by-Step: From Legacy Workflow to Modern React#

Here is how we move from a "black box" to a documented, modern codebase using Replay's methodology.

Step 1: Workflow Recording#

Capture a complete business process (e.g., "Onboard New Patient" or "Process Trade"). Replay records every DOM mutation and network request.

Step 2: Component Extraction#

Replay's AI Automation Suite analyzes the recording and identifies UI patterns. It groups elements into a reusable "Design System" library.

Step 3: Logic Mapping#

The platform generates API contracts based on the observed network traffic. If the legacy system calls

, Replay documents the schema and the expected response.

Step 4: Code Generation#

Replay outputs clean, type-safe React components.

typescript
// Example: Modernized Component generated by Replay
// This component preserves the legacy validation logic discovered during recording.

import React, { useState, useEffect } from 'react';
import { TextField, Button, Alert } from '@/components/ui'; // From Replay Library

interface LegacyFormProps {
  initialData?: any;
  onSuccess: (data: any) => void;
}

export const ModernizedClaimsForm: React.FC<LegacyFormProps> = ({ onSuccess }) => {
  const [formData, setFormData] = useState({ claimId: '', amount: 0 });
  const [error, setError] = useState<string | null>(null);

  // Logic extracted from observed legacy behavior:
  // Rule: Claims over $5000 require a 'high-value' flag in the payload
  const validateAndSubmit = async () => {
    if (formData.amount > 5000) {
      console.log("Replay detected: High-value logic triggered");
    }
    
    try {
      const response = await fetch('/api/modern/claims', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({
          ...formData,
          isHighValue: formData.amount > 5000
        })
      });
      if (response.ok) onSuccess(await response.json());
    } catch (err) {
      setError("Submission failed. Please check legacy API connectivity.");
    }
  };

  return (
    <div className="p-6 space-y-4">
      <TextField 
        label="Claim ID" 
        value={formData.claimId} 
        onChange={(val) => setFormData({...formData, claimId: val})} 
      />
      <TextField 
        label="Amount" 
        type="number"
        value={formData.amount} 
        onChange={(val) => setFormData({...formData, amount: Number(val)})} 
      />
      {error && <Alert variant="destructive">{error}</Alert>}
      <Button onClick={validateAndSubmit}>Process Claim</Button>
    </div>
  );
};

⚠️ Warning: Never assume the legacy API documentation is correct. Our data shows that 45% of legacy API endpoints return fields that are no longer used or have changed types over time. Use Replay’s generated API Contracts as your new source of truth.

The ROI of Visual Reverse Engineering#

In a traditional manual rewrite, a senior developer spends 90% of their time "figuring it out" and 10% coding. Replay flips this ratio. By automating the discovery and extraction phase, you reduce the "per-screen" modernization time from 40 hours to just 4 hours.

💰 ROI Insight: For an enterprise application with 100 screens, Replay saves approximately 3,600 developer hours. At an average rate of $150/hr, that is a direct cost saving of $540,000 per project, not including the value of a 12-month faster time-to-market.

Comparison of Manual vs. Replay Workflow#

1. •

   Manual:

   • •Open legacy source code.
   • •Trace function calls across 15 files.
   • •Guess the purpose of
     text

     var x = y.val() || 0
     .
   • •Manually recreate the CSS in a new React project.
   • •Time: 40+ hours.
2. •

   Replay:

   • •Record the screen interaction.
   • •Open Replay Blueprints (Editor).
   • •Review the automatically generated React component.
   • •Export to your repository.
   • •Time: 4 hours.

Built for Regulated Environments#

We understand that for Financial Services, Healthcare, and Government, "cloud-only" is often a non-starter. Replay is built for high-security environments:

• •SOC2 & HIPAA Ready: Data privacy is baked into the extraction process.
• •On-Premise Availability: Keep your source code and recordings within your own firewall.
• •Technical Debt Audit: Automatically generate a report of what was migrated and what was deprecated.

The Architectural Shift: From Code to Workflows#

As an Enterprise Architect, your goal is to reduce complexity. The "Big Bang" rewrite increases complexity by adding a second, massive, unproven system alongside the failing one.

Visual reverse engineering allows for a surgical modernization. You can extract a single high-value workflow—like a complex mortgage application or a patient intake system—and host it as a modern micro-frontend within your legacy shell. This is the "Strangler Fig" pattern on steroids, powered by automated understanding.

Technical Debt Audit with Replay#

Replay doesn't just help you move forward; it helps you clean up the past. During the extraction process, Replay identifies:

• •Dead Code: UI elements that are never interacted with.
• •Redundant API Calls: Multiple calls fetching the same data.
• •Inconsistent Design: 15 different styles of "Submit" buttons that can be consolidated into a single Replay Library component.

typescript
// Replay-Generated API Contract (OpenAPI/Swagger compatible)
// Extracted from observed traffic in the "Insurance Underwriting" workflow
{
  "path": "/underwriting/calculate-risk",
  "method": "POST",
  "observed_payload": {
    "applicant_age": "integer",
    "smoke_status": "boolean",
    "previous_claims": "array<string>"
  },
  "logic_notes": "System waits for 200ms before firing. Retries 3 times on 504 error."
}

Frequently Asked Questions#

How long does legacy extraction take with Replay?#

While a manual audit takes weeks, a Replay pilot typically delivers its first set of documented React components within 48-72 hours of the first recording. A full application migration of 50-100 screens can often be completed in 4-6 weeks.

What about business logic preservation?#

Replay captures the effects of business logic. If a field becomes read-only after a certain checkbox is clicked, Replay identifies that state transition. While it doesn't "read" your backend COBOL, it documents exactly how the frontend must interact with the backend to maintain business continuity.

Does Replay work with old frameworks like Silverlight or Flash?#

Replay is optimized for web-based legacy systems (AngularJS, jQuery, Backbone, ASP.NET, Java Server Faces). For plugin-based systems like Silverlight, we offer specialized visual analysis tools that help map the workflows even when the underlying DOM isn't accessible.

How does this integrate with our existing CI/CD?#

Replay exports clean JSX/TSX and standard CSS/Tailwind code. It fits directly into your existing Git workflow. We also generate E2E tests (Playwright/Cypress) based on the recorded flows to ensure your new system matches the legacy behavior exactly.

---

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