M&A Due Diligence for Legacy Codebases: A CTO's Visual Forensic Guide

Your M&A target claims their legacy system is a "stable foundation," but the reality is usually a $3.6 trillion mountain of technical debt hidden behind a flickering JSP interface or a bloated Silverlight monolith. In the high-stakes environment of mergers and acquisitions, the "black box" of legacy software is the single greatest risk to valuation. When performing diligence legacy codebases ctos often find themselves trapped between two bad options: trusting a 200-page PDF of outdated documentation or spending $200k on a manual audit that takes three months to complete.

Traditional code audits focus on what the code says it does. Visual forensics focuses on what the software actually does. By the time a deal reaches the final stages, you don't just need a list of vulnerabilities; you need a roadmap for integration. This is where Replay transforms the process, moving from manual line-by-line inspection to automated visual reverse engineering.

TL;DR:

• •The Problem: 67% of legacy systems lack documentation, and 70% of rewrites fail, making M&A integration a high-risk gamble.
• •The Solution: Visual Forensics. Instead of reading dead code, record live workflows to extract the "ground truth" of the application architecture.
• •The Tool: Replay reduces the time to document and modernize legacy UIs by 70%, turning months of discovery into days of actionable data.
• •The Outcome: Faster valuation, reduced technical debt, and a clear path to a modern React-based Design System.

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The $3.6 Trillion Blind Spot in Tech Diligence#

The global technical debt crisis has reached a staggering $3.6 trillion. For a CTO overseeing an acquisition, this isn't an abstract figure—it’s the cost of the 18-month rewrite timeline that will inevitably follow the deal. When performing diligence legacy codebases ctos must account for the fact that most legacy systems are "undocumented by design." Original architects have left, the tech stack is deprecated, and the UI logic is tightly coupled with brittle backend services.

Industry experts recommend that technical diligence should not just be a security scan. It must be a functional assessment. If you cannot map the user journey to the underlying component structure, you are buying a liability, not an asset. According to Replay's analysis, manual screen-to-component mapping takes an average of 40 hours per screen. In a 50-screen enterprise application, that’s 2,000 man-hours just to understand what you’ve inherited.

Video-to-code is the process of recording a user’s interaction with a legacy system and using AI-driven visual analysis to automatically generate documented React components and architectural maps. This methodology eliminates the "documentation gap" by creating a living record of the system's current state.

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Why Traditional Diligence Fails Legacy Codebases#

Most M&A audits rely on static analysis tools (SAST) and manual interviews. While SAST can find a SQL injection vulnerability, it cannot tell you that the "Order Management" module is a 15,000-line jQuery file that will break if you try to update the CSS.

For effective diligence legacy codebases ctos need to see the "Flows"—the actual architectural pathways data takes through the UI. Without this, you are estimating integration costs based on guesswork.

Comparison: Manual Audit vs. Visual Forensic Audit (Replay)#

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Visual Forensics: A New Framework for Diligence#

To properly perform diligence legacy codebases ctos should adopt a "Visual Forensic" framework. This involves three distinct phases: Discovery, Extraction, and Documentation.

1. Discovery via "Flows"#

Instead of digging through a repo with 10,000 files, you start by recording the most critical business workflows. As you record, Replay Flows maps the relationship between the UI elements and the underlying logic. This creates an immediate visual architecture of the legacy system.

2. Extraction via "Blueprints"#

Once the flows are recorded, the next step is extracting the "DNA" of the application. This isn't just a screenshot; it’s the extraction of design tokens, spacing, typography, and functional logic. Replay’s AI Automation Suite parses the video recording to identify recurring patterns, effectively building a Design System from a legacy mess.

3. Documentation and Modernization#

The final output isn't a PDF—it’s a Library of documented React components. This allows the acquiring company to see exactly how much effort is required to port the legacy UI into their existing modern stack.

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The Technical Reality: From Legacy Mess to Clean React#

When performing diligence legacy codebases ctos are often horrified by the "spaghetti" logic found in older frameworks like ASP.NET WebForms or early Angular. Visual reverse engineering abstracts this complexity.

Consider a legacy "User Profile" screen. In the old system, the logic might be buried in a global script file:

javascript
// Legacy Spaghetti (Found during diligence)
function validateAndSubmit() {
    var name = document.getElementById('user_name').value;
    if (name == "") {
        alert("Name is required");
        return false;
    }
    // Hardcoded API calls mixed with UI logic
    $.ajax({
        url: "/api/v1/updateUser?id=" + window.currentUserId,
        method: "POST",
        data: { name: name },
        success: function() {
            location.reload();
        }
    });
}

Using Replay, this functional intent is captured visually and converted into a clean, modern React component. This allows the CTO to evaluate the "modernization readiness" of the codebase. Instead of a vague "it needs a rewrite," you get a functional prototype of the future state.

typescript
// Replay Generated Output: Modernized React Component
import React, { useState } from 'react';
import { Button, Input, useToast } from '@acme-corp/design-system';

interface UserProfileProps {
  userId: string;
  initialName: string;
  onUpdate: (newName: string) => Promise<void>;
}

export const UserProfileEditor: React.FC<UserProfileProps> = ({ 
  userId, 
  initialName,
  onUpdate 
}) => {
  const [name, setName] = useState(initialName);
  const { toast } = useToast();

  const handleSave = async () => {
    try {
      await onUpdate(name);
      toast({ title: "Profile updated successfully" });
    } catch (error) {
      toast({ title: "Update failed", variant: "destructive" });
    }
  };

  return (
    <div className="p-6 space-y-4 border rounded-lg shadow-sm">
      <h3 className="text-lg font-semibold">Edit Profile</h3>
      <Input 
        value={name} 
        onChange={(e) => setName(e.target.value)} 
        placeholder="Enter user name"
      />
      <Button onClick={handleSave} disabled={!name}>
        Save Changes
      </Button>
    </div>
  );
};

By seeing this side-by-side comparison during the diligence legacy codebases ctos can accurately price the integration. You aren't just buying the old code; you're buying the blueprint for the new code.

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Mapping the Architecture with Replay Flows#

One of the biggest risks in M&A is the "hidden dependency." You think you are acquiring a simple frontend, but it turns out to be tightly coupled to a legacy mainframe via a series of undocumented SOAP calls.

Replay's "Flows" feature allows you to visualize these dependencies. By recording the user journey, the platform identifies every state change and data request.

Industry experts recommend looking for three specific "Red Flags" during visual forensics:

1. •Circular UI Dependencies: Screens that require multiple cross-page refreshes to update a single state.
2. •Hardcoded Business Logic: Validation rules that exist only in the UI layer and are not replicated in the API.
3. •Inconsistent Design Tokens: 50 different shades of blue and 12 different button styles across 10 screens, indicating a lack of a centralized design system.

Modernizing Legacy UI is significantly easier when these patterns are identified before the deal closes.

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Security, Compliance, and Regulated Environments#

In industries like Financial Services, Healthcare, and Government, diligence isn't just about code quality—it's about compliance. When conducting diligence legacy codebases ctos must ensure that the tools used do not expose sensitive data (PII/PHI).

Replay is built for these high-stakes environments. With SOC2 compliance, HIPAA-readiness, and the option for On-Premise deployment, it allows for deep forensic analysis without moving sensitive data into the cloud. During the diligence process, recordings can be sanitized, ensuring that the forensic team sees the structure of the application without seeing the data of the target company's customers.

According to Replay's analysis, 85% of enterprise legacy systems in the healthcare sector contain hardcoded data handling logic that violates modern privacy standards. Finding these during the diligence phase—rather than post-acquisition—can save millions in potential fines and remediation costs.

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Implementing the Visual Forensic Strategy#

How does a CTO actually roll this out during a live deal? The process follows a streamlined path:

1. •Identify Critical Paths: Determine the 10-20 workflows that represent 80% of the business value.
2. •Record and Map: Use Replay to record these workflows. This takes hours, not days.
3. •Generate the Blueprint: Let the AI Automation Suite analyze the recordings to extract the component library and architectural flows.
4. •Analyze the "Modernization Gap": Compare the extracted React components against your internal design system.
5. •Calculate the "True Cost": Use the 70% time savings metric to provide a realistic integration budget.

For more on how to structure this, see our guide on Technical Debt in M&A.

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Frequently Asked Questions#

How does visual reverse engineering differ from standard screen recording?#

Standard screen recording produces a flat video file. Replay’s visual reverse engineering captures the underlying DOM structure, CSS properties, and functional state changes. It converts the "visuals" into structured data (JSON/TypeScript) that can be used to generate actual code, whereas a screen recording is just a reference for a manual developer.

Can Replay handle legacy frameworks like Flash, Silverlight, or Mainframe Green Screens?#

Yes. Because Replay uses visual analysis combined with DOM mapping (where available), it can document any interface that a user can interact with. For older pixel-based technologies, the AI Automation Suite uses computer vision to identify patterns and layout structures, creating a modern React-based "Blueprint" of the legacy interface.

How does this speed up the 18-month average enterprise rewrite timeline?#

The majority of a rewrite's timeline is spent in "Discovery" and "Requirements Gathering"—essentially trying to figure out what the old system does. Replay automates this discovery phase. By providing developers with documented React components and clear architectural flows from day one, you skip the 6-9 months of manual reverse engineering, leading to an average 70% reduction in time-to-market.

Is the code generated by Replay production-ready?#

Replay generates high-quality TypeScript/React components that follow modern best practices. While a senior architect will still want to review the integration with specific backend services, the generated code is "clean" and follows the design system tokens extracted during the recording. It provides a 90% starting point, compared to starting from a blank IDE.

How do we handle PII (Personally Identifiable Information) during a diligence recording?#

Replay includes built-in PII masking and data-scrubbing features. During the recording process, sensitive fields can be automatically blurred or replaced with synthetic data. Furthermore, for highly regulated industries, Replay offers on-premise deployments so that no data ever leaves your secure environment during the diligence legacy codebases ctos process.

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The Future of Technical Diligence#

The era of "guessing" what’s under the hood of a legacy acquisition is over. As technical debt continues to mount, the ability to rapidly deconstruct and document inherited software is a competitive necessity. By moving to a visual forensic model, CTOs can provide the board with more than just a "Go/No-Go" recommendation—they can provide a Day 1 execution plan.

Whether you are looking at a fintech platform with a 20-year-old frontend or a healthcare provider with a fragmented UI, the goal remains the same: minimize risk and maximize the speed of integration. Replay provides the visibility needed to turn a legacy liability into a modern asset.

Ready to modernize without rewriting? Book a pilot with Replay