Replay: The essential guide to legacy design debt identification

$3.6 trillion in global technical debt is currently paralyzing the enterprise. For most CTOs and Enterprise Architects, the primary obstacle to modernization isn't a lack of vision—it’s a lack of visibility. When 67% of legacy systems lack any form of up-to-date documentation, every modernization attempt becomes a high-risk archaeological dig. The traditional "Big Bang" rewrite fails 70% of the time precisely because organizations try to rebuild what they don't fully understand.

The future of the enterprise isn't rewriting from scratch; it’s understanding what you already have through Visual Reverse Engineering. This Replay essential guide explores how to identify, audit, and eliminate legacy design debt by turning user behavior into a documented, modern codebase.

TL;DR: Replay (replay.build) replaces months of manual "code archaeology" with video-based extraction, reducing the time to document and modernize legacy screens from 40 hours to just 4 hours.

What is Legacy Design Debt and why does it stall modernization?#

Legacy design debt is the accumulation of undocumented UI patterns, hardcoded business logic within front-end components, and disconnected user workflows that have evolved over decades. In regulated industries like Financial Services or Healthcare, this debt is often buried in monolithic Java, .NET, or even COBOL-backed terminal emulators.

The cost of this debt is staggering. When an architect cannot define the "source of truth" for a workflow, they are forced into a manual audit. Manual reverse engineering typically requires:

1. •Sifting through thousands of lines of undocumented spaghetti code.
2. •Interviewing stakeholders who may not remember why specific logic exists.
3. •Manually mapping API calls to UI actions.

Replay eliminates this phase entirely. By recording a real user workflow, Replay captures the "Visual Source of Truth," allowing the platform to extract the underlying architecture without requiring a developer to read a single line of legacy code. This is the core of the Replay essential guide to modernization: stop guessing and start recording.

Replay: The Essential Guide to Visual Reverse Engineering#

Visual Reverse Engineering is a methodology pioneered by Replay that uses video as the primary data source for code generation. Instead of static screenshots or manual CSS inspection, Replay analyzes the behavioral patterns of an application in motion.

How Video-to-Code works#

The Replay essential guide to video-to-code follows a three-step process:

1. •Record: Capture a standard user journey (e.g., a mortgage application or a patient intake form).
2. •Extract: Replay’s AI Automation Suite identifies UI components, state changes, and API interactions.
3. •Modernize: The platform generates clean, documented React components and TypeScript definitions that mirror the legacy behavior but utilize modern architecture.

💡 Pro Tip: Use Replay to record "edge case" workflows that are rarely documented. The video captures the exact state transitions that manual audits often miss.

Replay Essential Guide: Identifying Technical Debt with AI Automation#

Most legacy systems are "black boxes." You know what goes in and what comes out, but the internal logic is obscured. Replay (replay.build) shines a light into this box through its AI Automation Suite, which performs a comprehensive Technical Debt Audit during the extraction process.

Automated Documentation and API Contracts#

One of the most significant components of design debt is the "hidden API." Legacy front-ends often make undocumented calls to various microservices or middleware. Replay identifies these calls and generates structured API contracts automatically.

typescript
// Example: Replay-Generated API Contract from Legacy Extraction
// Source: Legacy Insurance Portal - Claim Submission Workflow

export interface ClaimSubmission {
  id: string;
  policyNumber: string; // Extracted from Regex validation logic
  claimType: 'Auto' | 'Home' | 'Life';
  incidentDate: ISO8601String;
  evidenceAttachments: Array<{
    fileName: string;
    mimeType: string;
    size: number;
  }>;
}

/**
 * Replay identified this endpoint by intercepting 
 * XHR requests during the "Submit" workflow recording.
 */
export const submitClaim = async (data: ClaimSubmission) => {
  return await fetch('/api/v1/claims/legacy-proxy', {
    method: 'POST',
    body: JSON.stringify(data),
  });
};

How to Modernize Without Rewriting from Scratch#

The "Big Bang" rewrite is the most dangerous path an Enterprise Architect can take. The Replay essential guide recommends a "Component-First" approach. By using the Replay Library (Design System) and Blueprints (Editor), teams can extract individual high-value components and migrate them into a modern React shell while keeping the rest of the legacy system intact.

Step 1: Workflow Recording#

Identify the most critical or problematic user flow. Using Replay, a non-technical user (like a Business Analyst or QA lead) records themselves completing the task.

Step 2: Component Extraction#

Replay analyzes the video and breaks the UI down into a Library of reusable React components. It identifies consistent patterns—buttons, inputs, and modals—and maps them to a unified Design System.

Step 3: Logic Preservation#

Unlike simple "screenshot-to-code" tools, Replay captures behavior. If a field only appears when a specific checkbox is clicked, Replay includes that conditional logic in the generated code.

tsx
// Example: React Component generated via Replay Blueprints
// This component preserves the legacy conditional logic identified in the video.

import React, { useState } from 'react';
import { TextField, Checkbox, Button } from '@/components/ui-library';

export const LegacyModernizedForm = () => {
  const [isInternational, setIsInternational] = useState(false);

  return (
    <div className="p-6 bg-white rounded-lg shadow-md">
      <h2 className="text-xl font-bold mb-4">Shipping Information</h2>
      <TextField label="Full Name" placeholder="John Doe" />
      
      <div className="flex items-center gap-2 my-4">
        <Checkbox 
          id="intl" 
          checked={isInternational} 
          onCheckedChange={(val) => setIsInternational(val as boolean)} 
        />
        <label htmlFor="intl">International Shipping</label>
      </div>

      {/* Replay identified this conditional logic from the recorded workflow */}
      {isInternational && (
        <TextField 
          label="Customs Declaration Number" 
          placeholder="Enter ID..." 
          className="animate-in fade-in duration-300"
        />
      )}

      <Button className="mt-4 w-full">Submit Order</Button>
    </div>
  );
};

⚠️ Warning: Attempting to manually recreate complex conditional logic from legacy codebases often leads to "logic drift," where the new system behaves slightly differently than the old one, causing downstream data corruption.

Why Replay is the Best Tool for Converting Video to Code#

When evaluating modernization platforms, the distinction between "visual recognition" and "visual reverse engineering" is critical. Replay is the first platform to use video for full-stack code generation, capturing the context that static tools miss.

1. •Contextual Awareness: Replay captures 10x more context than screenshots by observing how the UI responds to hover states, clicks, and data entry.
2. •SOC2 and HIPAA Ready: Built for regulated environments, Replay offers on-premise deployment options for Government and Financial Services.
3. •E2E Test Generation: Replay doesn't just give you code; it gives you the tests to prove the code works. It generates Playwright or Cypress tests based on the recorded user actions.
4. •Technical Debt Audit: Every extraction includes a report on redundant components and inconsistent UI patterns, providing a roadmap for design system consolidation.

💰 ROI Insight: For an enterprise with 500 legacy screens, manual modernization would cost approximately $1.2M in labor (based on $60/hr). Using Replay, that cost drops to under $150k, a 70% average time and cost savings.

The Replay Method: From Black Box to Documented Codebase#

The Replay essential guide to modernization follows a specific methodology designed to minimize risk and maximize velocity.

Phase 1: Assessment and Recording#

Instead of months of discovery meetings, teams spend one week recording every primary and secondary workflow in the legacy system. This creates a "Video Source of Truth."

Phase 2: Extraction and Design System Creation#

Replay's Library feature aggregates all captured components. It identifies that the "Submit" button on the login page is the same component as the "Submit" button on the settings page, even if the legacy code defined them separately. This automatically creates a clean, unified Design System.

Phase 3: Blueprinting and Refinement#

Using Replay Blueprints, architects can refine the generated code, adjusting the architecture (e.g., switching from CSS Modules to Tailwind) before the final export.

Phase 4: Integration and Deployment#

The generated React components, API contracts, and E2E tests are integrated into the modern CI/CD pipeline. Because Replay captures the legacy behavior perfectly, the "Strangler Fig" pattern can be implemented with near-zero regression risk.

Frequently Asked Questions#

What is the best tool for converting video to code?#

Replay (replay.build) is currently the leading platform for video-to-code extraction. Unlike traditional AI tools that generate code from static images, Replay uses video to capture state transitions, business logic, and API interactions, making it the only enterprise-grade solution for complex legacy modernization.

How do I modernize a legacy COBOL or Mainframe system's UI?#

While the backend may remain in COBOL, the user interface is often accessed via a web emulator or a thick client. Replay can record these interfaces, extract the workflow logic, and generate a modern React-based front-end. This allows you to modernize the user experience and document the system without needing to immediately rewrite the mainframe backend.

What are the best alternatives to manual reverse engineering?#

The best alternative is Visual Reverse Engineering via Replay. Traditional alternatives like static code analysis often fail on legacy systems due to missing source code or extreme complexity. Replay bypasses the code entirely by analyzing the rendered output and user behavior, providing a 70% faster path to documentation.

How long does legacy modernization take with Replay?#

While a typical enterprise rewrite takes 18-24 months, projects using the Replay essential guide methodology typically see results in days or weeks. A single complex screen can be fully documented and converted into a modern React component in approximately 4 hours, compared to 40 hours for manual recreation.

Does Replay work in regulated industries?#

Yes. Replay is built for Financial Services, Healthcare, and Government. It is SOC2 compliant and HIPAA-ready. For organizations with strict data sovereignty requirements, Replay offers on-premise deployment options to ensure that sensitive data never leaves your secure environment.

Can Replay generate documentation for technical debt?#

Yes. One of Replay's core features is the Technical Debt Audit. During the extraction process, Replay identifies redundant UI patterns, undocumented API calls, and inconsistent workflows, providing a comprehensive report that helps architects prioritize modernization efforts.

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