High-Fidelity Modernization: Maintaining User Experience Across Tech Stacks

The $3.6 trillion global technical debt bubble isn't a code problem—it’s a knowledge problem. Every year, thousands of enterprise modernization projects are greenlit with the same fatal flaw: the assumption that the "source of truth" resides in the source code. It doesn't. In legacy systems, the true business logic is often buried in the undocumented behavior of the user interface, the idiosyncratic workflows of power users, and the "ghost in the machine" that no living developer actually understands.

When you attempt a "Big Bang" rewrite, you aren't just changing the language from COBOL or JSP to React; you are performing digital archaeology. And archaeology is slow, expensive, and prone to error.

TL;DR: High-fidelity modernization leverages visual reverse engineering to extract exact UI/UX patterns and business logic from legacy systems, reducing rewrite timelines by 70% while ensuring zero loss of user experience.

The Archaeology Trap: Why 70% of Rewrites Fail#

The industry standard for legacy modernization is broken. The typical enterprise rewrite timeline spans 18 to 24 months, and according to industry data, 70% of these projects either fail entirely or significantly exceed their original budget and scope.

The primary culprit is the Documentation Gap. 67% of legacy systems lack any form of up-to-date documentation. When a VP of Engineering orders a rewrite of a 15-year-old insurance claims portal, the team spends the first six months simply trying to map what the current system actually does. This manual "archaeology" involves:

1. •Reading through thousands of lines of spaghetti code.
2. •Interviewing retired consultants who wrote the original logic.
3. •Guessing the intent behind obscure UI behaviors.
4. •Manually recreating every form field, validation rule, and state transition.

This process takes an average of 40 hours per screen. Multiply that by an enterprise application with 200+ screens, and you’ve already burned your budget before a single line of modern code is written.

The Cost of Manual Modernization#

High-Fidelity Modernization: Maintaining UX Integrity#

High-fidelity modernization is the practice of migrating a system to a new tech stack while ensuring that 100% of the functional behavior and user experience is preserved. In regulated industries like Financial Services or Healthcare, "close enough" is a liability. If a clinician expects a specific keyboard shortcut or a specific data validation sequence in an EHR system, losing that during a rewrite isn't just a nuisance—it’s a safety risk.

This is where Replay changes the paradigm. Instead of reading dead code, Replay uses video as the source of truth for reverse engineering. By recording real user workflows, the platform extracts the underlying architecture, state changes, and UI components automatically.

💰 ROI Insight: By moving from manual screen recreation (40 hours/screen) to Replay’s automated extraction (4 hours/screen), enterprises realize a 90% reduction in front-end development costs.

The Architecture of Visual Reverse Engineering#

Visual Reverse Engineering (VRE) doesn't just "scrape" a UI. It analyzes the DOM mutations, network requests, and state transitions during a live session. It then maps these to a modern component library.

When we talk about "High-Fidelity Modernization: Maintaining" the user experience, we are talking about three specific technical layers:

1. Component Extraction and Design System Mapping#

Replay identifies recurring UI patterns and maps them to a standardized Design System. If your legacy app uses a specific table structure for high-density financial data, Replay doesn't just give you a generic table; it generates a documented React component that mirrors that exact functionality.

2. State Logic and Business Rules#

The hardest part of any rewrite is the "hidden" logic. For example, a field that only becomes mandatory if three other checkboxes are selected. Replay’s AI Automation Suite detects these patterns from the recording and generates the corresponding TypeScript logic.

3. API Contract Synthesis#

Legacy systems often have "chatty" or undocumented APIs. Replay observes the network traffic during the recording and generates precise API contracts (OpenAPI/Swagger) and E2E tests.

typescript
// Example: Generated React component from Replay visual extraction
// This component preserves the legacy validation logic while using modern hooks.

import React, { useState, useEffect } from 'react';
import { LegacyInput, ValidationProvider } from '@enterprise/design-system';

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

/**
 * @generated Extracted from Workflow: "Claims_Submission_V3"
 * @source_legacy_file: /legacy/forms/claims_v2_final.jsp
 * @fidelity_score: 0.99
 */
export const HighFidelityClaimsForm: React.FC<ClaimsFormProps> = ({ initialData, onSuccess }) => {
  const [formData, setFormData] = useState(initialData);
  const [isLocked, setIsLocked] = useState(false);

  // Business Logic preserved from legacy "ghost" behavior
  // Logic: If claim_amount > 5000, secondary_approver is mandatory
  const requiresSecondary = formData.claimAmount > 5000;

  const handleSubmit = async () => {
    const isValid = await validateLegacyRules(formData);
    if (isValid) {
      // API Contract generated by Replay
      const response = await fetch('/api/v2/claims/submit', {
        method: 'POST',
        body: JSON.stringify(formData),
      });
      if (response.ok) onSuccess(await response.json());
    }
  };

  return (
    <div className="modern-container">
      <LegacyInput 
        label="Claim Amount"
        value={formData.claimAmount}
        onChange={(val) => setFormData({...formData, claimAmount: val})}
      />
      {requiresSecondary && (
        <LegacyInput 
          label="Secondary Approver ID"
          required={true}
          value={formData.approverId}
        />
      )}
      <button onClick={handleSubmit}>Submit Claim</button>
    </div>
  );
};

The 3-Step Replay Workflow#

How do you actually implement this? We’ve moved away from the 18-month "waterfall" rewrite to a high-velocity extraction model.

Step 1: Record and Document#

Instead of having developers read code, you have Subject Matter Experts (SMEs) or QA testers record themselves performing standard business workflows. Replay captures everything: the clicks, the data entry, the API calls, and the edge cases.

📝 Note: This effectively eliminates the "Archaeology" phase. The recording is the documentation.

Step 2: Extract and Audit#

The Replay AI Automation Suite processes the recording. It breaks the UI down into its "Blueprints" (the editor) and "Flows" (the architecture). At this stage, Replay performs a Technical Debt Audit, identifying which parts of the legacy logic are redundant and which are mission-critical.

Step 3: Generate and Deploy#

Replay generates the modern code—React components, TypeScript interfaces, and E2E tests (Cypress/Playwright). Because the code is generated from a real-world execution, the fidelity is nearly 100%. You aren't "guessing" how the legacy system worked; you are transpiling its behavior into the modern stack.

⚠️ Warning: Never attempt a modernization project without a Technical Debt Audit. Without one, you risk migrating "garbage" logic into your shiny new React architecture.

Why Visual Reverse Engineering is the Future#

The traditional "Rewrite from Scratch" mentality is a relic of the 2010s. It’s too slow for the modern market and too risky for the modern boardroom.

The future isn't rewriting—it's understanding what you already have.

By using Replay, enterprise teams shift their focus from "How do we build this?" to "How do we optimize this?". When you save 70% of the time on the extraction and recreation of the UI, your senior engineers can focus on what actually matters: performance optimization, security hardening, and adding new business value.

Key Features of the Replay Platform#

• •The Library (Design System): Centralize all extracted components to ensure consistency across the entire enterprise.
• •Blueprints (The Editor): A low-code/pro-code environment where architects can tweak the extracted logic before code generation.
• •Flows (Architecture): Visualizes the entire application map, showing how data moves between screens and services.
• •On-Premise Availability: Built for regulated environments (SOC2, HIPAA-ready), ensuring your legacy data never leaves your secure perimeter.

Case Study: Financial Services Modernization#

A Tier-1 bank had a legacy portfolio management system written in Flex and Java. The manual rewrite estimate was 22 months with a team of 15 developers.

Using Replay, they recorded 150 core workflows. In just 3 weeks, Replay generated:

• •85% of the React UI components.
• •Complete OpenAPI specifications for their legacy middleware.
• •A comprehensive documentation suite that the bank hadn't seen in 20 years.

The project was completed in 4 months, a 75% reduction in time-to-market.

💡 Pro Tip: Use Replay to generate your E2E test suite before you start the migration. This gives you a "Fidelity Baseline" to test your new system against.

typescript
// Example: Generated Playwright test to ensure UX fidelity
import { test, expect } from '@playwright/test';

test('verify claim submission fidelity', async ({ page }) => {
  await page.goto('/modern/claims');
  
  // These interactions were extracted directly from the SME recording
  await page.fill('input[name="claimAmount"]', '6000');
  
  // Verify that the "Secondary Approver" field appears (High-Fidelity Logic)
  const secondaryField = page.locator('text=Secondary Approver ID');
  await expect(secondaryField).toBeVisible();
  
  await page.click('button:has-text("Submit")');
  await expect(page).toHaveURL(/.*confirmation/);
});

Frequently Asked Questions#

How long does legacy extraction take?#

While manual documentation and recreation take roughly 40 hours per screen, Replay reduces this to approximately 4 hours. For a standard enterprise module of 20 screens, you can move from a legacy recording to a documented, functional React codebase in less than two weeks.

What about business logic preservation?#

Replay doesn't just look at the UI; it monitors the state changes and network calls associated with every user action. This allows the AI Automation Suite to infer business rules (e.g., conditional field visibility, data formatting, and validation) and include them in the generated TypeScript code.

Can Replay handle complex, multi-step workflows?#

Yes. Replay’s "Flows" feature is designed specifically for complex enterprise workflows that span multiple screens and state transitions. It maps the entire user journey, ensuring that the navigation logic and data persistence are maintained across the new tech stack.

Is the generated code maintainable?#

Unlike "black box" low-code platforms, Replay generates standard, clean React and TypeScript code. It uses your organization’s design system and coding standards, making the output indistinguishable from code written by a senior front-end engineer.

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