Stop Guessing: Automating the Bridge from Legacy UI to Modern Design Systems

The $3.6 trillion global technical debt isn't just a balance sheet liability; it is an existential threat to enterprise agility. Most organizations are currently trapped in a "modernization paradox": they cannot innovate because they are tethered to legacy UI, yet they cannot migrate because the institutional knowledge required to rewrite those systems has long since left the building.

The traditional "Big Bang" rewrite is a failed strategy. Industry data confirms that 70% of legacy rewrites either fail entirely or significantly exceed their timelines. When you spend 18 to 24 months attempting to replicate a system that no one fully understands, you aren't modernizing—you are performing expensive digital archaeology.

The future of the enterprise isn't rewriting from scratch; it’s understanding what you already have. By automating the bridge between legacy interfaces and modern design systems, we can finally move from the "black box" era to a documented, maintainable codebase in weeks rather than years.

TL;DR: Automating the bridge from legacy UI to modern design systems via visual reverse engineering eliminates the "archaeology" phase of modernization, reducing per-screen effort from 40 hours to 4 hours while ensuring 100% logic parity.

The High Cost of Manual Archaeology#

Why do most modernization projects stall? Because 67% of legacy systems lack any form of usable documentation. Before a single line of React can be written, senior engineers are forced to spend months clicking through ancient screens, sniffing network traffic, and trying to decipher obfuscated COBOL or JSP logic.

This manual extraction is the ultimate productivity killer. On average, it takes 40 hours of manual labor to document, design, and develop a single complex legacy screen into a modern equivalent. Multiply that by an enterprise footprint of 500+ screens, and you have a multi-year roadmap that is obsolete before it ships.

Comparing Modernization Strategies#

Automating the Bridge: Visual Reverse Engineering#

The breakthrough in modernization isn't better AI coding assistants; it’s Visual Reverse Engineering. At Replay, we treat the video of a user workflow as the single source of truth. Instead of guessing what a button does, we record the actual execution of the legacy system and extract the underlying architecture.

By recording real user workflows, Replay identifies the UI patterns, the data structures, and the API contracts required to support them. This "automating the bridge" approach moves the needle from manual reconstruction to automated extraction.

💰 ROI Insight: By switching from manual documentation to Replay, enterprises reduce the time spent per screen from 40 hours to just 4 hours—a 90% reduction in engineering overhead.

From Legacy Mess to Clean React Components#

When we talk about automating the bridge, we mean generating functional, production-ready code that maps directly to your new design system. Replay doesn't just "scrape" the UI; it understands the intent.

Here is an example of a component generated via Replay’s extraction engine, mapping an old table-based legacy form to a modern, type-safe React component using a standardized Design System:

typescript
// Generated via Replay Blueprint Editor
// Source: Claims_Processing_v2_Legacy (JSP)
// Target: Enterprise Design System (React + Tailwind)

import React, { useState, useEffect } from 'react';
import { Button, Input, Card, Alert } from '@/components/design-system';
import { useClaimsStore } from '@/store/claims';

interface LegacyFormProps {
  claimId: string;
  onSuccess: (data: any) => void;
}

export function ClaimsMigrationForm({ claimId, onSuccess }: LegacyFormProps) {
  const { fetchLegacyData, submitModernizedClaim } = useClaimsStore();
  const [loading, setLoading] = useState(false);
  const [formData, setFormData] = useState<any>(null);

  // Replay extracted the exact API contract from the legacy network trace
  useEffect(() => {
    const loadData = async () => {
      const data = await fetchLegacyData(claimId);
      setFormData(data);
    };
    loadData();
  }, [claimId]);

  const handleSubmit = async (e: React.FormEvent) => {
    e.preventDefault();
    setLoading(true);
    // Preserving business logic validation rules identified during recording
    if (formData.amount > 10000 && !formData.supervisorId) {
      return Alert.error("High-value claims require supervisor ID.");
    }
    await submitModernizedClaim(formData);
    onSuccess(formData);
    setLoading(false);
  };

  if (!formData) return <SkeletonLoader />;

  return (
    <Card title="Claim Details - Modernized">
      <form onSubmit={handleSubmit} className="space-y-4">
        <Input 
          label="Policy Number" 
          value={formData.policy_no} 
          disabled 
        />
        <Input 
          label="Claim Amount" 
          type="number"
          value={formData.amount}
          onChange={(val) => setFormData({...formData, amount: val})}
        />
        <Button type="submit" isLoading={loading}>
          Update Claim Record
        </Button>
      </form>
    </Card>
  );
}

The Three Pillars of the Replay Ecosystem#

Automating the bridge requires more than just a screen recorder. It requires a comprehensive platform that can handle the complexity of regulated industries like Financial Services and Healthcare.

1. The Library (Design System Alignment)#

Most legacy systems are a patchwork of inline styles and dead CSS. Replay’s Library feature allows you to map legacy UI elements to your modern Design System. When Replay "sees" a legacy submit button, it doesn't just copy the hex code; it maps it to your

component in your React library.

2. The Flows (Architecture Mapping)#

Understanding a single screen is easy. Understanding how 50 screens connect to form a "Mortgage Application" is hard. Flows automatically generates architectural diagrams from recorded sessions, showing exactly how data moves through the system.

3. The Blueprints (AI-Assisted Editor)#

The Blueprint Editor is where the bridge is built. It takes the recorded metadata—DOM structures, network calls, and user interactions—and allows architects to refine the generated code. This is where you audit technical debt and decide which legacy "quirks" to keep and which to kill.

⚠️ Warning: Do not attempt to automate 100% of the logic without human oversight. The goal of automating the bridge is to remove 90% of the manual grunt work, leaving the high-level architectural decisions to your senior talent.

Step-by-Step: How to Automate Your Migration#

Step 1: Workflow Recording#

Instead of reading 500 pages of outdated documentation, have your Subject Matter Experts (SMEs) perform their daily tasks while Replay records the session. Replay captures the DOM, the network requests, and the state changes.

Step 2: Visual Extraction#

Replay’s AI Automation Suite analyzes the recording. It identifies recurring UI patterns and groups them into potential React components. It also generates API Contracts based on the actual JSON/XML payloads captured during the session.

Step 3: Blueprint Mapping#

In the Replay Blueprint Editor, engineers map the extracted elements to the modern Design System. This is where you define how the legacy "black box" logic should be represented in the new architecture.

Step 4: Code Generation & E2E Testing#

Replay generates the React components, TypeScript interfaces, and—crucially—E2E Tests. Because Replay knows exactly how the legacy system responded to specific inputs, it can generate Playwright or Cypress tests to ensure the new system behaves identically.

typescript
// Example: Generated E2E Test ensuring logic parity
import { test, expect } from '@playwright/test';

test('verify claim validation parity', async ({ page }) => {
  await page.goto('/modernized-claims/123');
  await page.fill('input[name="amount"]', '15000');
  await page.click('button[type="submit"]');
  
  // Replay knows the legacy system showed this error for this input
  const error = page.locator('.alert-error');
  await expect(error).toContainText('High-value claims require supervisor ID');
});

Why Conventional Wisdom is Wrong#

For years, consultants have preached that you must "re-think the business process" before you modernize. While well-intentioned, this is why projects take 24 months. By the time you’ve re-thought the process, the market has moved.

Automating the bridge allows for a "Move, then Improve" strategy.

1. •Move: Extract the existing logic into a modern stack (React/Node/TypeScript) in weeks.
2. •Improve: Now that you have a documented, tested, and modern codebase, you can iterate and improve the business process with 10x the velocity of the legacy system.

💡 Pro Tip: Focus on "High-Value, High-Pain" modules first. Don't try to migrate the entire monolith at once. Use Replay to extract the most critical workflows to prove ROI to stakeholders within the first 30 days.

Built for the Regulated Enterprise#

We understand that Financial Services, Healthcare, and Government agencies cannot simply upload their legacy data to a public cloud. Replay is built for these environments:

• •SOC2 & HIPAA Ready: Data privacy is baked into the extraction process.
• •On-Premise Available: Keep your source code and recordings within your own perimeter.
• •PII Masking: Automated masking of sensitive data during the recording and extraction phase.

Frequently Asked Questions#

How long does legacy extraction take with Replay?#

While a manual rewrite of a standard enterprise module takes 18-24 months, Replay customers typically see a fully documented and extracted codebase in 2 to 8 weeks. The automated extraction of a single complex screen takes minutes, with a few hours of refinement in the Blueprint Editor.

What about business logic preservation?#

This is the biggest fear in modernization. Replay preserves business logic by capturing the actual state transitions and network responses of the legacy system. By generating E2E tests based on real user sessions, we provide a "safety net" that ensures the modernized version maintains 100% logic parity with the legacy system.

Does Replay support mainframe or terminal-based systems?#

Yes. As long as the system is accessed via a web interface or a terminal emulator that can be rendered in a browser environment, Replay can record the workflow and extract the underlying data patterns and UI structures.

How does this handle technical debt?#

Replay includes a Technical Debt Audit feature. During extraction, it identifies redundant API calls, unused UI elements, and non-standard styling. This allows architects to "clean as they go" rather than simply porting technical debt from one language to another.

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