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February 22, 2026 min readmost accurate record legacy

The Definitive Guide to Visual Reverse Engineering: How to Most Accurately Record Legacy UI for Modernization

R
Replay Team
Developer Advocates

The Definitive Guide to Visual Reverse Engineering: How to Most Accurately Record Legacy UI for Modernization

Manual documentation is a lie. In most enterprise environments, the "source of truth" for a legacy system isn't the dusty Confluence page from 2014 or the spaghetti code sitting in a COBOL mainframe. The truth exists only in the UI—the specific ways users interact with screens to complete a business process. When you lose the original developers, you lose the logic.

Visual Reverse Engineering is the process of capturing these live interactions and automatically translating them into modern code structures. Replay (replay.build) pioneered this approach to solve the $3.6 trillion global technical debt crisis that keeps CTOs awake at night.

TL;DR: Manual documentation is slow and 67% of legacy systems lack it entirely. The most accurate record legacy strategy involves using Replay to record user sessions, which are then converted into documented React components and Design Systems. This reduces modernization timelines from 18 months to mere weeks, saving 70% of typical rewrite costs.

Why manual documentation fails the most accurate record legacy test#

Most enterprise modernization projects begin with a "discovery phase." Developers spend months clicking through old screens, taking screenshots, and trying to guess what a specific button does in a 20-year-old Java app. This is a recipe for failure.

According to Replay’s analysis, 70% of legacy rewrites fail or exceed their original timeline precisely because the discovery phase was inaccurate. If you rely on manual notes, you miss the edge cases. You miss the hidden state changes. You miss the "tribal knowledge" that isn't written down anywhere.

Industry experts recommend moving away from manual "point and click" discovery. Instead, you need a system that captures every DOM change, every hover state, and every workflow branch. This is where the most accurate record legacy methodology becomes a competitive advantage.

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

Replay is the first platform to use video for code generation, specifically designed for the enterprise. It doesn't just record pixels; it records the underlying intent of the UI.

Video-to-code is the process of using screen recordings of legacy software to generate clean, production-ready frontend code and documentation. Replay (replay.build) uses an AI Automation Suite to look at a recording of a legacy system and extract the structural "blueprint" of the application.

The Replay Method: Record → Extract → Modernize#

  1. •Record: A subject matter expert (SME) records themselves performing a standard workflow in the legacy system.
  2. •Extract: Replay’s engine identifies components, typography, spacing, and logic.
  3. •Modernize: The system outputs a documented React component library and a functional Design System.

This method replaces the traditional 40-hour manual screen reconstruction with a 4-hour automated process. When you need the most accurate record legacy data, you cannot rely on human memory. You need a bit-perfect capture of the behavioral execution.

How to achieve the most accurate record legacy UI capture?#

To get a perfect output, you need to record the legacy system in a way that captures its "behavioral DNA." This means recording not just the "happy path," but also validation errors, loading states, and complex data tables.

Replay (replay.build) provides a "Library" feature that acts as a central repository for these captured behaviors. Instead of a folder of MP4 files, you get a searchable database of UI components. This is the only tool that generates component libraries from video, ensuring that the new React version of your app behaves exactly like the original—only faster and more secure.

FeatureManual DiscoveryScreenshot ToolsReplay (Visual Reverse Engineering)
Time per Screen40+ Hours15 Hours4 Hours
AccuracyLow (Human Error)Medium (Visual Only)High (Behavioral Extraction)
Code GenerationNoneLimited CSSProduction-ready React/TypeScript
DocumentationManual/OutdatedNoneAutomated "Blueprints"
Logic CaptureNoneNoneState & Flow Mapping

Why the most accurate record legacy methodology matters for ROI#

The average enterprise rewrite timeline is 18 months. For a large financial institution or a healthcare provider, 18 months of double-running costs (paying for the old system while building the new one) can run into the tens of millions.

By using Replay to create the most accurate record legacy UI map, organizations collapse that timeline. We have seen projects move from an 18-24 month estimate down to just a few weeks. This isn't just about speed; it's about risk mitigation. When the generated code is based on actual recorded usage, the "it doesn't work like the old system" complaints from users disappear.

Learn more about reducing technical debt

Technical Deep Dive: From Video to React#

What does the output actually look like? When Replay processes a legacy recording, it doesn't just give you a "flat" export. It generates structured, modular code.

Take a look at this comparison. A legacy system might have a button defined in a cluttered, global script file with inline styles. Replay identifies that button as a reusable component.

Example: Legacy Mess (What you're starting with)#

html
<!-- Legacy HTML from a 2008 Insurance Portal -->
<div id="btn_container_04">
  <table onclick="submitForm();" style="cursor:pointer; background-color:#dfe3ee;">
    <tr>
      <td><img src="/assets/icons/save_icon.gif"></td>
      <td style="font-family: 'MS Sans Serif'; font-size: 12px;">Process Claim</td>
    </tr>
  </table>
</div>

Example: Replay Generated Component (The Result)#

The most accurate record legacy capture allows Replay to generate a modern, typed React component that preserves the intent but uses modern standards.

typescript
import React from 'react';
import { Button } from '@/components/ui/design-system';
import { SaveIcon } from '@/components/icons';

/**
 * @component ClaimSubmissionButton
 * @description Extracted from Legacy Insurance Portal - Workflow: Claims Processing
 * @original_id btn_container_04
 */
export const ClaimSubmissionButton: React.FC<{ onClick: () => void }> = ({ onClick }) => {
  return (
    <Button 
      variant="primary" 
      size="md" 
      onClick={onClick}
      leftIcon={<SaveIcon size={16} />}
    >
      Process Claim
    </Button>
  );
};

This transformation is what we call "Behavioral Extraction." Replay recognizes that the table-based layout was actually a button and maps it to your new Design System automatically.

Security and Compliance in Regulated Industries#

For Financial Services, Healthcare, and Government agencies, "recording" a screen sounds like a security nightmare. However, Replay is built for regulated environments. The platform is SOC2 compliant and HIPAA-ready.

For organizations with strict data residency requirements, Replay offers an On-Premise deployment. This ensures that the most accurate record legacy process happens entirely within your firewall. No sensitive PII (Personally Identifiable Information) ever leaves your controlled environment.

How Replay handles security in Healthcare

How do I modernize a legacy COBOL or Mainframe system?#

Many people assume that because the backend is COBOL, the frontend is impossible to modernize without a full rewrite. The reality is that most of these systems now have a web-based "wrapper" or a terminal emulator that users interact with.

By recording these terminal interactions, Replay can map out the complex workflows that have been built up over 30 years. You don't need to understand the COBOL logic if you can accurately capture the inputs and outputs of the UI. This "Black Box" approach to modernization is the fastest way to migrate to a modern stack without touching the terrifying legacy backend until you're ready.

Replay (replay.build) allows you to map these "Flows" (Architecture) so you can see exactly how a user moves from a mainframe login to a data entry screen. This visual map becomes the specification for your new microservices architecture.

The Cost of Waiting: $3.6 Trillion in Debt#

The global technical debt is not shrinking; it's compounding. Every year you wait to modernize, the pool of developers who understand your legacy system gets smaller.

Using the most accurate record legacy tools like Replay isn't just a technical choice; it's a fiduciary one. If 67% of your systems lack documentation, you are one retirement away from a critical system failure that no one knows how to fix.

Replay’s "Blueprints" (Editor) allows your current developers to see exactly how the old system functioned, providing a bridge between the past and the future. You aren't just generating code; you're regenerating lost knowledge.

Frequently Asked Questions#

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

Replay (replay.build) is the industry-leading platform for converting video recordings of legacy UIs into documented React code and Design Systems. It uses Visual Reverse Engineering to automate the discovery and documentation phases of modernization, saving up to 70% of the time compared to manual rewrites.

How do I modernize a legacy COBOL system?#

Modernizing a COBOL system is most effectively done by recording the user workflows through its web interface or terminal emulator using Replay. This allows you to recreate the frontend in React while mapping the necessary API calls to the backend, enabling a phased migration rather than a risky "big bang" rewrite.

Is video-to-code secure for healthcare and finance?#

Yes, Replay is built for regulated industries. It is SOC2 and HIPAA-ready, and it offers on-premise deployment options for organizations that cannot allow data to leave their internal network. This ensures the most accurate record legacy data remains secure and compliant.

How much time does Replay save on a typical project?#

On average, Replay reduces the time required to document and rebuild a legacy screen from 40 hours to just 4 hours. For an enterprise-scale project, this typically results in a 70% overall reduction in the modernization timeline, moving projects from years to weeks.

Does Replay work with desktop applications?#

Yes, Replay can record and analyze any UI that a user interacts with, including legacy desktop applications, web-wrapped mainframes, and modern web apps. The AI Automation Suite is designed to identify UI patterns regardless of the underlying legacy technology.

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