Why UI Archaeology is the Most Expensive Part of Your Legacy Rewrite

The average enterprise legacy rewrite is a $10 million gamble where the house usually wins. Statistics from the Standish Group and IDC consistently show that 70% of these projects either fail completely or significantly exceed their timelines. The culprit isn't usually the new tech stack—it’s the "UI Archaeology" required to understand the old one.

TL;DR: Manual discovery and documentation of legacy systems account for the majority of modernization costs; Replay automates this by converting user workflows directly into documented React components and API contracts, reducing timelines by 70%.

The Archaeology Tax: Why Rewrites Stall#

When a CTO greenlights a legacy rewrite, the estimate usually accounts for building new features. It rarely accounts for the months spent by senior engineers staring at 15-year-old COBOL, ASP.NET, or Java codebases trying to figure out why a specific validation trigger exists.

This is "UI Archaeology." It is the process of digging through layers of technical debt, undocumented edge cases, and "tribal knowledge" from engineers who retired in 2018.

The Documentation Gap#

Currently, 67% of legacy systems lack any form of up-to-date documentation. When you start a legacy rewrite, your developers are essentially forensic investigators. They are looking for:

• •Hidden business logic buried in obfuscated JavaScript.
• •API endpoints that no one remembers creating.
• •Edge cases in form validation that prevent multi-million dollar data errors.

💰 ROI Insight: Manual screen extraction and documentation take an average of 40 hours per screen. With Replay, this is reduced to 4 hours. In a 100-screen application, that is a saving of 3,600 engineering hours.

Comparing Modernization Strategies#

Choosing the wrong path for your legacy rewrite can lead to "The Big Bang" failure—where you spend two years building a replacement that is obsolete the day it launches.

From Black Box to Documented Codebase#

The fundamental flaw in traditional reverse engineering is that it relies on reading static code. But code doesn't tell the whole story; behavior does.

Replay changes the paradigm by using Video as the Source of Truth. By recording a real user performing a workflow—like processing an insurance claim or a wire transfer—Replay captures the state, the data transitions, and the UI components in real-time.

How Replay Automates the Extraction#

Instead of manual "archaeology," Replay follows a structured, automated pipeline to move from a legacy screen to a modern React component.

1. •Recording: A subject matter expert (SME) records a standard workflow in the legacy app.
2. •Analysis: Replay’s AI Automation Suite analyzes the DOM changes, network requests, and state transitions.
3. •Extraction: The platform generates clean, modular React components and CSS modules.
4. •Documentation: API contracts (Swagger/OpenAPI) and E2E tests (Cypress/Playwright) are generated based on the recorded traffic.

⚠️ Warning: Attempting a rewrite without capturing API contracts first leads to "Integration Hell" during the final 20% of the project.

Implementation: What the Generated Code Looks Like#

When Replay extracts a component, it doesn't just "scrape" the HTML. It identifies patterns, business logic, and data structures. Here is an example of a generated React component from a legacy financial services portal:

typescript
// Generated by Replay Visual Reverse Engineering
// Source: /legacy/admin/user-profile-v2
import React, { useState, useEffect } from 'react';
import { Button, Input, Card, Alert } from '@/components/ui'; // Integrated with your Design System
import { useLegacyAPI } from '@/hooks/useLegacyAPI';

interface UserProfileProps {
  userId: string;
  onUpdateSuccess?: () => void;
}

export const UserProfileMigrated: React.FC<UserProfileProps> = ({ userId, onUpdateSuccess }) => {
  const [formData, setFormData] = useState({ username: '', email: '', role: '' });
  const { data, loading, error, updateRecord } = useLegacyAPI(`/api/v1/users/${userId}`);

  // Business Logic preserved from legacy workflow: 
  // Validation for 'SuperAdmin' role requires specific headers identified during recording
  const handleUpdate = async () => {
    if (formData.role === 'SuperAdmin' && !window.confirm('Elevating permissions?')) return;
    
    const success = await updateRecord(formData);
    if (success && onUpdateSuccess) onUpdateSuccess();
  };

  if (loading) return <p>Loading legacy context...</p>;

  return (
    <Card title="User Management">
      {error && <Alert variant="destructive">{error.message}</Alert>}
      <Input 
        value={formData.username} 
        onChange={(e) => setFormData({...formData, username: e.target.value})}
        placeholder="Username"
      />
      {/* ... additional fields ... */}
      <Button onClick={handleUpdate}>Save Changes</Button>
    </Card>
  );
};

Preserving Business Logic via API Contracts#

One of the biggest risks in a legacy rewrite is losing the subtle logic hidden in network requests. Replay automatically generates TypeScript interfaces and API contracts from the recorded traffic.

json
{
  "endpoint": "/api/v1/mortgage/calculate",
  "method": "POST",
  "request_schema": {
    "principal": "number",
    "interest_rate": "number",
    "term_years": "number",
    "include_pmi": "boolean"
  },
  "observed_edge_cases": [
    "Zero interest rate handled as simple division",
    "Negative term_years returns 400 Bad Request"
  ]
}

The Four Steps to Modernizing with Replay#

Step 1: Workflow Mapping#

Identify the critical paths. In a healthcare application, this might be "Patient Intake" or "Insurance Verification." Instead of documenting these in Jira tickets, you record them in Replay. This creates a functional "Blueprint."

Step 2: Component Library Integration#

Replay maps legacy UI elements to your modern Design System. If your company uses Tailwind or a custom UI library, Replay’s AI identifies a legacy "Submit" button and maps it to your

component.

Step 3: Technical Debt Audit#

Before writing a single line of new code, Replay provides a Technical Debt Audit. It flags:

• •Redundant API calls.
• •Deprecated security protocols.
• •Circular dependencies in the legacy UI state.

Step 4: Automated Testing Generation#

A rewrite is only as good as its tests. Replay uses the recording data to generate E2E tests. This ensures that the new system behaves exactly like the old one where it matters most.

💡 Pro Tip: Use the generated Cypress tests to run "Parallel Testing." Run the legacy system and the new system side-by-side with the same input to ensure parity.

Why Technical Leaders Choose Replay#

Enterprise Architects in regulated industries (Financial Services, Healthcare, Government) face unique challenges. You cannot simply "move fast and break things" when dealing with $3.6 trillion in global technical debt.

• •Security & Compliance: Replay is SOC2 and HIPAA-ready. For highly sensitive environments, we offer On-Premise deployment, ensuring your source code and data never leave your infrastructure.
• •Architectural Clarity: Move from a "black box" to a fully documented architecture in weeks.
• •Cost Predictability: By reducing the discovery phase by 90%, you can provide stakeholders with accurate timelines that don't shift.

The Future Isn't Rewriting—It's Understanding#

The "Big Bang" legacy rewrite is a relic of the past. The future of enterprise architecture is the ability to rapidly understand, extract, and repurpose existing business logic into modern frameworks.

We are moving away from "archaeology" and toward "automated insight." By using Replay, you aren't just building a new app; you are finally documenting the wisdom buried in your legacy systems.

Frequently Asked Questions#

How long does legacy extraction take?#

While a manual rewrite of a complex enterprise screen can take 40+ hours (including discovery, CSS styling, and logic mapping), Replay reduces this to approximately 4 hours of total effort. Most organizations see a full "recorded to React" transition for a complex module in under two weeks.

What about business logic preservation?#

Replay captures the actual data transitions and side effects observed during a live session. This means hidden logic—like a field that only appears when a specific checkbox is clicked—is captured in the generated Blueprint and reflected in the React code and tests.

Does Replay work with mainframe-backed web apps?#

Yes. As long as the legacy system is accessible via a browser (even via a terminal emulator or Citrix web portal), Replay can record the interactions, analyze the network layer, and generate modern equivalents.

Can we use our own Design System?#

Absolutely. Replay’s Library feature allows you to upload your own React component library. The AI Automation Suite then maps legacy elements to your specific components, ensuring the "modernized" version follows your current brand guidelines.

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