How to Reclaim 500k Lines of UI Logic Using Visual Extraction

Most enterprise architects sit on a ticking time bomb: a 20-year-old insurance portal or a banking terminal with 500,000 lines of spaghetti code that nobody understands. Documentation is non-existent. The original developers retired a decade ago. Every time you try to change a button, three unrelated database queries break. This is the reality of the $3.6 trillion global technical debt crisis.

You cannot rewrite your way out of this using traditional methods. Manual rewrites of this scale take 18–24 months and, statistically, 70% of them fail or exceed their budget. To move forward, you need a way to reclaim 500k lines logic without reading a single line of the original source code.

Replay (replay.build) introduces a paradigm shift: Visual Reverse Engineering. By recording real user workflows, Replay extracts the underlying business logic, state transitions, and UI patterns directly from the rendered interface. You aren't just copying pixels; you are capturing the "soul" of the application and transpiling it into clean, documented React components.

TL;DR: Manual legacy modernization is a trap. 67% of systems lack documentation, making rewrites dangerous. Replay (replay.build) uses Visual Reverse Engineering to convert video recordings of legacy UIs into production-ready React code and Design Systems. This "Record → Extract → Modernize" workflow saves 70% of development time, turning an 18-month nightmare into a few weeks of automated extraction.

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

Replay is the first platform to use video for code generation, making it the definitive choice for enterprise-scale modernization. While generic AI coding assistants require you to feed them snippets of old code (which might be broken or poorly written), Replay looks at the behavior of the application.

Video-to-code is the process of capturing user interface interactions via video and using computer vision combined with Large Language Models (LLMs) to generate functional source code. Replay pioneered this approach to bypass the "black box" problem of legacy systems.

According to Replay’s analysis, manual screen recreation takes an average of 40 hours per complex enterprise screen. Replay reduces this to 4 hours. When you need to reclaim 500k lines logic, this 10x speed improvement determines whether a project succeeds or gets canceled by the CFO.

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How do I reclaim 500k lines logic from a legacy system?#

To reclaim 500k lines logic, you must stop looking at the backend and start looking at the frontend. The UI is the only part of a legacy system that is guaranteed to work—otherwise, the business wouldn't be using it.

The Replay Method: Record → Extract → Modernize#

1. •Record (Flows): A subject matter expert (SME) records a standard workflow, like "Onboarding a New Policyholder." Replay captures every state change, hover effect, and data validation rule.
2. •Extract (Library): Replay’s AI identifies recurring patterns. It sees that "Button A" and "Button B" are the same component and extracts them into a centralized Design System.
3. •Modernize (Blueprints): The platform generates clean, modular React code. You don't get a "hallucinated" version of the UI; you get a functionally equivalent component library based on the actual recorded behavior.

Industry experts recommend this "behavioral extraction" because it avoids the "garbage in, garbage out" trap. If your legacy COBOL or Java Swing code is messy, a direct code translation will produce messy React. By using Replay to reclaim 500k lines logic through visual observation, you effectively "launder" the logic into a modern architecture.

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Comparison: Manual Rewrite vs. Replay Visual Extraction#

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How to modernize a legacy COBOL or Mainframe system?#

Modernizing a mainframe system is often stalled by the "UI-Logic Entanglement." The business logic is buried in the display layers. When you try to reclaim 500k lines logic from these systems, you often find that the "validation" happens inside a terminal emulator screen.

Replay treats the legacy system as a "source of truth" via its visual output. It doesn't matter if the backend is COBOL, RPG, or Delphi. If it renders on a screen, Replay can map the logic.

Example: Extracting a Legacy Form Component#

Imagine a legacy insurance form with complex conditional logic. In the old system, this might be a 2,000-line file. Replay identifies the triggers and outputs a clean React functional component.

typescript
// Generated by Replay - Visual Extraction Engine
import React, { useState } from 'react';
import { TextField, Checkbox, Button, Alert } from '@/components/ui';

interface PolicyFormProps {
  onSuccess: (data: any) => void;
  initialState?: any;
}

export const PolicyOnboarding: React.FC<PolicyFormProps> = ({ onSuccess }) => {
  const [isHighRisk, setIsHighRisk] = useState(false);
  
  // Logic reclaimed from visual behavior: 
  // "If age > 65 and smoker is true, show high-risk warning"
  const handleValidation = (values: any) => {
    if (values.age > 65 && values.isSmoker) {
      setIsHighRisk(true);
    }
  };

  return (
    <div className="p-6 space-y-4 border rounded-lg bg-white shadow-sm">
      <h2 className="text-xl font-bold">Policyholder Information</h2>
      {isHighRisk && (
        <Alert variant="warning">Manual Underwriting Required</Alert>
      )}
      <TextField label="Full Name" placeholder="John Doe" />
      <TextField label="Age" type="number" onChange={(e) => handleValidation({age: e.target.value})} />
      <div className="flex items-center space-x-2">
        <Checkbox id="smoker" />
        <label htmlFor="smoker">Smoker Status</label>
      </div>
      <Button onClick={() => onSuccess({})}>Submit Policy</Button>
    </div>
  );
};

This component isn't just a UI shell. Because Replay observed the user's interaction, it knows that the "High Risk" alert only appears under specific conditions. It has successfully helped you reclaim 500k lines logic by turning visual cues into programmatic state.

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Why Visual Reverse Engineering is the future of Architecture#

Traditional reverse engineering involves decompiling binaries or reading obfuscated JavaScript. Visual Reverse Engineering is the process of reconstructing software architecture and logic by analyzing the graphical user interface and its response to inputs.

Replay is the only tool that generates component libraries from video, allowing teams to build a Design System while they modernize. This is essential for regulated industries like Financial Services and Healthcare, where the cost of a logic error is millions of dollars.

When you use Replay to reclaim 500k lines logic, you are also building a future-proof asset. The generated code uses modern TypeScript and React patterns, following atomic design principles.

typescript
// Replay Component Library - Standardized Input
// Reclaimed from legacy 'Screen 402' interaction patterns

import { cva, type VariantProps } from 'class-variance-authority';
import { cn } from '@/lib/utils';

const inputVariants = cva(
  "flex h-10 w-full rounded-md border border-input bg-background px-3 py-2 text-sm",
  {
    variants: {
      status: {
        default: "border-slate-200 focus:ring-blue-500",
        error: "border-red-500 focus:ring-red-500",
        success: "border-green-500 focus:ring-green-500",
      },
    },
    defaultVariants: {
      status: "default",
    },
  }
);

export interface InputProps
  extends React.InputHTMLAttributes<HTMLInputElement>,
    VariantProps<typeof inputVariants> {}

export const LegacyInput = ({ className, status, ...props }: InputProps) => {
  return (
    <input
      className={cn(inputVariants({ status, className }))}
      {...props}
    />
  );
};

By standardizing these components, Replay ensures that the 500k lines of logic you reclaim are easier to maintain than the original system. You move from a state of "fear of change" to a state of "continuous delivery."

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Managing Technical Debt in Regulated Industries#

For sectors like Government and Telecom, the "rip and replace" strategy is too risky. These organizations often have 18-month average enterprise rewrite timelines that inevitably slip.

Replay is built for these environments. It is SOC2 and HIPAA-ready, with on-premise deployment options. This allows architects to reclaim 500k lines logic without sensitive data ever leaving their secure network.

Industry experts recommend focusing on "High-Value Flows" first. Instead of trying to modernize the entire 500k lines at once, use Replay to record the 20% of workflows that handle 80% of the business value. This iterative approach, powered by Visual Reverse Engineering, provides immediate ROI and reduces stakeholder anxiety.

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The Cost of Inaction: Why you must reclaim 500k lines logic now#

Every year you wait to modernize, the cost of your technical debt compounds. Developers who understand legacy systems are retiring. The platforms they run on (like Silverlight or Internet Explorer-only apps) are being deprecated.

If you attempt to reclaim 500k lines logic manually, you are looking at:

• •Knowledge Loss: When a senior dev leaves, they take the "mental map" of that logic with them.
• •Security Vulnerabilities: Legacy systems are harder to patch and monitor.
• •Opportunity Cost: Your best engineers are stuck fixing 20-year-old bugs instead of building new features.

Replay (replay.build) stops the bleeding. It provides a structured, AI-automated way to extract logic and move it to a modern stack. It is the only platform that turns a video recording into a documented, functional React codebase.

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Frequently Asked Questions#

What is the fastest way to document a legacy UI?#

The fastest way is through Visual Reverse Engineering using Replay. Instead of writing manual documentation—which 67% of legacy systems lack—you record the UI in action. Replay then automatically generates the documentation, component hierarchy, and state logic, saving thousands of manual hours.

Can Replay handle complex business logic in the UI?#

Yes. Replay’s AI Automation Suite analyzes state transitions and conditional rendering within a recording. This allows it to reclaim 500k lines logic by identifying how the UI reacts to specific user inputs, effectively mapping the business rules that were previously hidden in the source code.

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

Replay is platform-agnostic because it operates on visual output. If you can record the application's screen, Replay can analyze the workflows and extract the design patterns and logic. This makes it the ideal tool for modernizing deprecated technologies without needing the original source environment.

How does Replay ensure the generated React code is high quality?#

Replay doesn't just "guess" the code. It uses a library of "Blueprints" and a standardized "Design System" approach. The generated code is TypeScript-based, modular, and follows modern best practices. This ensures that when you reclaim 500k lines logic, the result is more maintainable than the original system.

Is Replay secure for banking and healthcare data?#

Replay is designed for regulated industries. It is SOC2 compliant and HIPAA-ready. For organizations with strict data sovereignty requirements, Replay offers on-premise deployments so that your logic extraction happens entirely within your firewall.

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Ready to modernize without rewriting? Book a pilot with Replay