How a Fortune 500 Bank Saved $2.2M by Avoiding a Full Manual Rewrite

The most expensive phrase in enterprise architecture is: "We’ll just rewrite it from scratch."

Every year, global technical debt consumes $3.6 trillion in resources. For a Fortune 500 bank, this isn't just a line item; it’s a systemic risk. When a Tier-1 financial institution decided to modernize its core commercial lending platform—a monolithic beast comprising 140+ screens and two decades of undocumented business logic—they were quoted 24 months and an $8M budget for a "Big Bang" rewrite.

They chose a different path. By shifting from manual archaeology to Visual Reverse Engineering with Replay, they bypassed the rewrite trap, saving $2.2M and finishing the project in under six months.

TL;DR: By utilizing Visual Reverse Engineering to extract business logic and UI components directly from user workflows, enterprises can bypass the "Big Bang" rewrite failure rate of 70% and reduce modernization timelines by over 70%.

The Archaeology Problem: Why Rewrites Fail#

The standard approach to legacy modernization is flawed because it relies on "Software Archaeology." Architects spend months interviewing retired developers, digging through outdated Confluence pages, and trying to map spaghetti code to modern requirements.

Statistically, 67% of legacy systems lack any form of accurate documentation. When you attempt to rewrite these systems without a clear understanding of the "as-is" state, you aren't building a new system; you're guessing. This is why 70% of legacy rewrites either fail entirely or significantly exceed their original timelines.

The Cost of Manual Extraction#

In a manual rewrite, a senior engineer spends an average of 40 hours per screen just to understand the state management, API dependencies, and edge-case validation logic.

⚠️ Warning: Most "modernization" projects fail not because of the new technology stack, but because the hidden business logic in the old stack was never fully discovered until the new system crashed in production.

Case Study: The $2.2M Recovery#

A Fortune 500 bank faced a critical deadline. Their legacy JSP-based lending portal was no longer compliant with new accessibility standards and lacked the agility to integrate with modern FinTech APIs.

The initial estimate for a manual React migration was 18 months. The primary bottleneck? The "Black Box" problem. The original developers were gone, and the Java backend was a labyrinth of nested conditionals that governed loan eligibility.

The Replay Intervention#

Instead of reading 500,000 lines of Java, the bank's architecture team used Replay to record actual user workflows. By "playing" through the loan application process, Replay's engine captured the underlying data structures, API calls, and component hierarchies.

1. •Recording: Subject Matter Experts (SMEs) performed standard tasks.
2. •Extraction: Replay converted these recordings into documented React components.
3. •Audit: The platform generated a technical debt audit, identifying which 30% of the code was dead and didn't need migration.

💰 ROI Insight: The bank reduced the time spent per screen from 40 hours to 4 hours. Across 140 screens, this saved 5,040 engineering hours. At an average blended rate of $150/hr, that is $756,000 in direct labor savings alone, not including the $1.4M saved in avoided opportunity costs and hardware maintenance.

From Black Box to React: The Technical Shift#

The power of Visual Reverse Engineering lies in its ability to generate functional code that preserves business intent. Replay doesn't just "scrape" the UI; it maps the state transitions and side effects.

Example: Extracted Legacy Component#

Below is a simplified example of how Replay extracts a complex legacy form and prepares it for a modern React environment, including the preservation of business logic comments.

typescript
// Generated by Replay Visual Reverse Engineering
// Source: /legacy/loan-portal/origination-form.jsp
// Logic preserved: Eligibility check based on credit_score > 650

import React, { useState, useEffect } from 'react';
import { Button, Input, Alert } from '@/components/ui'; // From Replay Design System Library

export const LoanEligibilityForm = ({ userId }: { userId: string }) => {
  const [loading, setLoading] = useState(false);
  const [status, setStatus] = useState<'idle' | 'eligible' | 'denied'>('idle');

  // Replay extracted this logic from the legacy network trace and DOM state
  const handleValidation = async (values: any) => {
    setLoading(true);
    try {
      // API Contract generated by Replay Blueprints
      const response = await fetch(`/api/v1/verify-eligibility`, {
        method: 'POST',
        body: JSON.stringify({
          uid: userId,
          score: values.creditScore,
          amount: values.requestedAmount
        })
      });
      const { eligible } = await response.json();
      setStatus(eligible ? 'eligible' : 'denied');
    } finally {
      setLoading(false);
    }
  };

  return (
    <div className="p-6 space-y-4">
      <h2 className="text-xl font-bold">Loan Origination</h2>
      <Input label="Credit Score" name="creditScore" type="number" />
      <Input label="Requested Amount" name="requestedAmount" type="currency" />
      
      {status === 'denied' && (
        <Alert variant="destructive">Application does not meet minimum tier requirements.</Alert>
      )}
      
      <Button onClick={handleValidation} isLoading={loading}>
        Check Eligibility
      </Button>
    </div>
  );
};

Generating the API Contract#

One of the biggest hurdles in bank modernization is the lack of Swagger/OpenAPI documentation for legacy endpoints. Replay monitors the traffic during the recording phase to generate accurate API contracts.

yaml
# Generated by Replay AI Automation Suite
openapi: 3.0.0
info:
  title: Legacy Loan API (Extracted)
  version: 1.0.0
paths:
  /api/v1/verify-eligibility:
    post:
      summary: Extracted from LoanPortal workflow
      requestBody:
        content:
          application/json:
            schema:
              type: object
              properties:
                uid: { type: string }
                score: { type: integer }
                amount: { type: number }
      responses:
        '200':
          description: Success
          content:
            application/json:
              schema:
                type: object
                properties:
                  eligible: { type: boolean }
                  tier: { type: string }

The 5-Step Modernization Framework#

To replicate the success of the Fortune 500 bank, we recommend a structured approach to visual reverse engineering.

Step 1: Workflow Mapping#

Identify the critical paths. In banking, this might be "Open New Account" or "Process Wire Transfer." Instead of reading code, record an SME performing these actions in the legacy environment using the Replay recorder.

Step 2: Component Extraction#

Replay’s Blueprints editor analyzes the recording. It identifies recurring UI patterns and extracts them into a reusable Library. This becomes your new Design System, ensuring the modernized UI is consistent across all 140 screens.

Step 3: Logic Decoupling#

The AI Automation Suite analyzes the state changes during the recording. If a specific button click triggers a complex validation sequence, Replay documents that logic and suggests a modern TypeScript implementation.

Step 4: E2E Test Generation#

One of the highest risks in modernization is regression. Replay generates Cypress or Playwright E2E tests based on the recorded workflows. This ensures that the new React component behaves exactly like the legacy JSP page.

Step 5: Continuous Integration#

Deploy the new components using a Strangler Fig pattern. Since Replay provides the documentation and the code, you can swap legacy screens for modern ones incrementally without a "Big Bang" release.

💡 Pro Tip: Focus on "Read-Heavy" screens first. They are lower risk and provide immediate value to users, allowing you to refine your Design System before tackling complex "Write-Heavy" transactional logic.

Built for Regulated Environments#

For Financial Services and Healthcare, "Cloud-Only" is often a dealbreaker. Replay was designed with these constraints in mind:

• •SOC2 & HIPAA Ready: Data privacy is baked into the extraction process.
• •On-Premise Availability: Run the Replay engine entirely within your own VPC or data center.
• •No PII Leakage: Built-in masking ensures that sensitive customer data recorded during the extraction process is never stored or processed by AI models.

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

The $3.6 trillion technical debt crisis exists because we treat legacy systems as "trash" to be thrown away rather than "truth" to be understood. The Fortune 500 bank didn't save $2.2M by working harder; they saved it by working smarter—using video as the source of truth for their architecture.

When you can see exactly how a system functions, the fear of the "Black Box" evaporates. You move from a state of "archaeology" to a state of "engineering."

• •70% average time savings compared to manual rewrites.
• •From 18 months to weeks for full-scale enterprise migrations.
• •Automated Documentation that stays current with the code.

Frequently Asked Questions#

How does Replay handle "hidden" business logic not visible in the UI?#

While Replay is a Visual Reverse Engineering platform, it doesn't just look at pixels. It captures the network layer, the DOM mutations, and the state transitions. If a piece of logic happens on the backend, Replay identifies the API call, the payload, and the resulting UI change, allowing architects to map the "hidden" logic with 100% accuracy.

Can Replay work with extremely old systems (e.g., Mainframe green screens)?#

Yes. Replay can interface with terminal emulators and legacy web wrappers. As long as a user can interact with the system via a browser or terminal, Replay can record the workflow and begin the extraction process into modern web components.

What is the learning curve for the engineering team?#

Most Enterprise Architects are productive within 48 hours. The platform is designed to augment your existing workflow, not replace it. Your engineers still write code, but they start with 80% of the work—the discovery, the component scaffolding, and the API contracts—already completed.

How does this affect our technical debt?#

Replay includes a Technical Debt Audit feature. During extraction, it identifies redundant components, unused API endpoints, and circular dependencies in the legacy system. This allows you to "clean house" during the migration, ensuring the new system is leaner than the original.

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