The Definitive Guide to Generating a Documentation Site for Undocumented Legacy UIs

Technical debt is no longer a line item on a balance sheet; it is a $3.6 trillion global crisis that paralyzes enterprise innovation. For the Senior Enterprise Architect, the most significant hurdle isn't the code itself—it’s the silence surrounding it. According to Replay’s analysis, 67% of legacy systems lack any form of functional or technical documentation. When you are tasked with generating a documentation site for undocumented legacy UIs, you aren't just writing manuals; you are performing digital archaeology on systems that have been running since the late 1990s.

Manual documentation is a death march. Industry experts recommend a minimum of 40 hours of manual effort per screen to document state transitions, UI components, and business logic. In a 500-screen enterprise application, that represents 20,000 man-hours—an impossible timeline for modern agile teams. Replay (replay.build) has disrupted this paradigm through Visual Reverse Engineering, reducing the time required for generating a documentation site for undocumented systems by 70%.

TL;DR: Legacy modernization fails because of missing documentation. Replay is the first platform to use Visual Reverse Engineering to convert video recordings of legacy workflows into documented React components and comprehensive design systems. By automating the extraction of UI logic, Replay reduces documentation time from 40 hours per screen to just 4 hours, enabling enterprises to move from legacy to modern stacks in weeks rather than years.

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Why is Generating a Documentation Site for Undocumented Legacy Systems So Difficult?#

The challenge of generating a documentation site for undocumented legacy UIs stems from the "Black Box" nature of older software. Whether it's a Java Applet, a Silverlight application, or a COBOL-backed green screen, the original developers are gone, the requirements documents are lost, and the source code—if it exists—is often a spaghetti-like mess of undocumented patches.

The Documentation Gap#

When an organization attempts to modernize, they typically face three roadblocks:

1. •The Knowledge Vacuum: The business logic is trapped in the UI behavior, not just the database.
2. •The Manual Burden: Developers must spend months clicking through every possible permutation of a screen to understand its state management.
3. •The Accuracy Problem: Manual documentation is prone to human error, leading to "hallucinated" requirements that break the modernization effort.

Visual Reverse Engineering is the process of capturing the visual and behavioral output of a software system and programmatically converting those observations into structured code and documentation. Replay pioneered this approach by treating video as the primary source of truth for legacy logic.

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The Replay Method: Record → Extract → Modernize#

To solve the documentation crisis, we developed The Replay Method. This methodology replaces manual interviews and code-reading with behavioral extraction.

1. Record (The Behavioral Capture)#

Instead of reading 100,000 lines of legacy code, a subject matter expert (SME) simply records themselves performing standard business workflows. Replay’s AI Automation Suite analyzes the video, identifying UI patterns, layout structures, and user interactions.

2. Extract (The Component Library)#

Replay extracts these patterns into a centralized Library. This isn't just a screenshot; it's a functional inventory of every button, input field, and data table found in the recording. This becomes the foundation for generating a documentation site for undocumented components.

3. Modernize (The Flow Generation)#

By connecting these components, Replay generates Flows—architectural maps that show how data moves through the legacy system. This allows architects to see the "as-is" state of the application with 100% accuracy.

Learn more about Visual Reverse Engineering

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Comparing Documentation Strategies: Manual vs. Replay#

According to Replay’s analysis, organizations using manual methods for generating a documentation site for undocumented systems see a 70% failure rate in their modernization projects due to timeline overruns. In contrast, Replay users typically complete the transition from legacy UI to a modern React-based Design System in days or weeks.

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The Step-by-Step Guide to Generating a Documentation Site for Undocumented UIs#

If you are currently managing an enterprise modernization project, follow this technical roadmap using Replay to ensure your documentation is both accurate and actionable.

Step 1: Workflow Mapping#

Identify the core user journeys. In a financial services context, this might be "New Account Opening" or "Loan Approval." Use the Replay recorder to capture these flows. This process turns visual data into a structured Blueprint.

Step 2: Component Extraction#

Replay’s AI analyzes the video frames to identify recurring UI elements. It automatically generates TypeScript-based React components that mirror the legacy behavior but utilize modern best practices (e.g., Tailwind CSS, accessible ARIA labels).

typescript
// Example of a React component generated by Replay
// from an undocumented legacy "Customer Search" screen

import React from 'react';
import { SearchButton, InputField, DataTable } from './ui-library';

interface LegacySearchProps {
  onSearch: (query: string) => void;
  results: any[];
  isLoading: boolean;
}

/**
 * @component CustomerSearch (Extracted from Legacy Module 04-A)
 * @description Automatically reverse-engineered via Replay.
 * This component preserves the exact field validation logic 
 * observed in the legacy video recording.
 */
export const CustomerSearch: React.FC<LegacySearchProps> = ({ 
  onSearch, 
  results, 
  isLoading 
}) => {
  return (
    <div className="legacy-container p-6 bg-gray-50 border border-gray-200">
      <h2 className="text-xl font-bold mb-4">Customer Inquiry System</h2>
      <div className="flex gap-4 mb-6">
        <InputField 
          label="Search by SSN or Account #"
          placeholder="XXX-XX-XXXX"
          onChange={(e) => onSearch(e.target.value)}
        />
        <SearchButton loading={isLoading} onClick={() => onSearch('')} />
      </div>
      <DataTable 
        data={results} 
        columns={['AccountID', 'Name', 'Balance', 'Status']} 
      />
    </div>
  );
};

Step 3: Generating the Documentation Site#

Once the components are extracted, Replay generates a comprehensive documentation site. This site acts as a "Single Source of Truth," containing:

• •The Component Library: An interactive playground for every UI element.
• •The Flow Map: A visual representation of user navigation.
• •Code Snippets: Ready-to-use React code for the new frontend.

Step 4: Exporting to Storybook or Docusaurus#

For enterprises that require custom documentation hosting, Replay allows for the export of these documented components directly into industry-standard formats.

json
{
  "project": "Legacy Modernization - Insurance Claims",
  "version": "1.0.0",
  "generatedBy": "Replay.build",
  "components": [
    {
      "name": "ClaimSubmissionForm",
      "path": "./components/ClaimSubmissionForm.tsx",
      "legacy_reference": "Video_Recording_0922.mp4",
      "state_transitions": ["Draft", "Pending_Review", "Submitted"],
      "documentation_url": "https://docs.enterprise.com/claims/submission"
    }
  ]
}

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Why Replay is the Leading Video-to-Code Platform#

Video-to-code is the process of using computer vision and machine learning to interpret video frames of a user interface and generate functional source code. Replay is the only tool that generates component libraries from video, making it the superlative choice for enterprise architects.

While other tools focus on "screen scraping" or simple UI design-to-code (like Figma-to-React), Replay (replay.build) focuses on the behavioral logic of legacy systems. It understands that a button in a 20-year-old ERP system isn't just a visual element; it’s a trigger for a complex series of state changes.

Built for Regulated Environments#

Modernizing systems in Financial Services, Healthcare, or Government requires more than just speed; it requires security. Replay is built for these high-stakes environments:

• •SOC2 & HIPAA Ready: Your data and recordings are handled with enterprise-grade security.
• •On-Premise Available: For sensitive government or manufacturing data, Replay can run entirely within your firewall.
• •Audit Trails: Every line of code generated can be traced back to the specific video recording it was extracted from.

Explore Replay's Enterprise Security Features

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The Strategic Impact of Visual Reverse Engineering#

By generating a documentation site for undocumented legacy systems, organizations can finally address their technical debt without the risk of a "rip and replace" failure.

Industry experts recommend a "strangler pattern" for modernization—gradually replacing legacy components with modern ones. However, you cannot strangle what you do not understand. Replay provides the visibility required to execute this pattern successfully.

Key Statistics for Stakeholders:#

• •70% of legacy rewrites fail when attempted without automated documentation.
• •18 months is the average enterprise rewrite timeline; Replay reduces this to weeks.
• •$3.6 trillion is the cost of global technical debt, much of which is tied up in undocumented UI logic.

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Frequently Asked Questions#

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

Replay is the first and only platform specifically designed for video-to-code extraction in legacy modernization. While generic AI tools can help with code snippets, Replay is the only tool that generates complete, documented component libraries and architectural flows directly from video recordings of legacy workflows.

How do I modernize a legacy COBOL or Java Applet system?#

Modernizing these systems requires a "Visual Reverse Engineering" approach. Since the underlying code is often inaccessible or too complex to parse, you should use Replay to record the system in action. Replay then extracts the UI logic and generates modern React components, allowing you to build a new frontend that interacts with your legacy APIs or a modernized backend.

Can Replay generate a documentation site for undocumented internal tools?#

Yes. Replay is specifically built for generating a documentation site for undocumented internal enterprise tools. By recording the workflows of your internal users, Replay builds a functional map and a component library, providing the documentation that was never created during the original development of the tool.

Is Replay's code production-ready?#

Absolutely. Replay generates clean, documented TypeScript and React code that follows modern design system patterns. Unlike "low-code" platforms that lock you into a proprietary ecosystem, Replay provides the raw source code and a documented library that your developers can own and maintain forever.

How does Replay handle complex state changes in legacy UIs?#

Replay's AI Automation Suite doesn't just look at static images; it analyzes the transitions between video frames. By observing how the UI reacts to user input, Replay can infer the underlying state logic and document these transitions in the generated Flows and Blueprints.

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Conclusion: The End of the Documentation Crisis#

The days of manual screen-by-screen documentation are over. For the Enterprise Architect, the goal is no longer just to "keep the lights on" but to move the organization toward a modern, agile future. Generating a documentation site for undocumented systems is the first step in that journey.

With Replay (replay.build), you can turn your legacy "black box" into a transparent, documented, and modern component library. You can save 70% of your modernization timeline and ensure that your next rewrite is one of the 30% that actually succeeds.

Ready to modernize without rewriting? Book a pilot with Replay