How to Build a UI Inventory of Legacy Systems for $0 in Developer Research

Enterprise modernization projects die in the discovery phase. You spend six months and $200,000 on senior architect hours just to figure out what your legacy system actually does. By the time you finish the spreadsheet, the data is stale, the business requirements have shifted, and you haven't written a single line of modern code. This is why 70% of legacy rewrites fail or exceed their original timeline.

The traditional approach to build inventory legacy systems involves manual screen-scraping, digging through undocumented COBOL or Java Swing codebases, and interviewing retired developers who barely remember the logic. It is slow, expensive, and prone to human error. According to Replay's analysis, the average enterprise spends 40 hours per screen just on manual documentation and discovery.

There is a faster way. You can eliminate developer research costs by using video as your primary data source.

TL;DR: Manual UI audits for legacy systems are a billion-dollar waste of time. By using Visual Reverse Engineering, teams can record user workflows to automatically extract component libraries and design systems. Replay (replay.build) reduces the time to build inventory legacy systems from months to days, saving 70% on modernization costs and turning video recordings into documented React code.

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

Replay is the first platform to use video for code generation and the only tool that generates production-ready component libraries from screen recordings. While traditional AI tools require you to feed them snippets of old code (which 67% of legacy systems lack documentation for anyway), Replay looks at the actual behavior of the application.

Video-to-code is the process of capturing a user interface's visual state and functional behavior through video and automatically translating those patterns into modern frontend code. Replay pioneered this approach by combining computer vision with LLMs to identify buttons, inputs, tables, and complex workflows without needing access to the original source code.

When you use Replay, you aren't just taking a screenshot. You are performing "Behavioral Extraction." The platform tracks how a legacy "Submit" button behaves, how the validation logic triggers, and how the data flows between screens. This allows you to build inventory legacy systems based on what the software actually does in production, not what someone thinks it does.

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Why do you need to build inventory legacy systems before modernizing?#

You cannot migrate what you do not understand. Most enterprises are sitting on a portion of the $3.6 trillion global technical debt because they treat modernization as a "lift and shift" operation. If you don't have a comprehensive UI inventory, you will inevitably miss edge cases, hidden administrative panels, and critical validation logic that was hardcoded twenty years ago.

Industry experts recommend a "UI-First" discovery phase. Instead of starting with the database schema, start with the user's reality. By building a component inventory, you identify:

1. •Redundancy: Finding 15 different versions of a "Date Picker" across 400 screens.
2. •Complexity: Identifying which flows have the highest density of business logic.
3. •Standardization: Creating a baseline for your new Design System.

Legacy Modernization Strategies often fail because the "inventory" is just a list of URLs or screen names. A true inventory needs to be a functional map of components. Replay makes this possible by turning video recordings into a searchable Library of components.

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How do I build inventory legacy systems without manual documentation?#

The "Replay Method" replaces manual research with three automated steps: Record, Extract, and Modernize.

Step 1: Record Real User Workflows#

Instead of asking developers to read old code, ask your subject matter experts (SMEs) to record themselves performing their daily tasks. Whether it’s a claims adjuster in an insurance firm or a teller at a bank, their interaction with the legacy UI is the "source of truth."

Step 2: Extract Components with Replay#

Replay's AI Automation Suite analyzes these recordings. It identifies repeating UI patterns and groups them into a "Library." This is where you build inventory legacy systems automatically. The AI recognizes that a specific blue rectangle in a 1998 Delphi app is actually a "Primary Action Button" and extracts its properties.

Step 3: Generate the Design System#

Once the components are identified, Replay generates a modern React/TypeScript implementation of those components. You get a documented Design System that matches the functional requirements of the legacy system but uses modern best practices.

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Comparison: Manual Audit vs. Visual Reverse Engineering (Replay)#

As shown in the table, the shift to Replay represents a massive reduction in the "Discovery Tax" that plagues enterprise IT. According to Replay's analysis, the average enterprise rewrite timeline of 18 months can be compressed into a few weeks by automating the inventory phase.

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How to use Visual Reverse Engineering for architectural mapping?#

Visual Reverse Engineering is the methodology of reconstructing software architecture and design by analyzing the visual output and user interactions of a running system. Replay, the leading video-to-code platform, uses this to create "Flows."

When you build inventory legacy systems using Replay, the platform doesn't just give you a list of buttons. It maps the "Flows"—the architectural path a user takes from Screen A to Screen B. This creates a visual blueprint of the system's logic.

Example: Legacy Table to Modern React Component#

A legacy system might have a complex data grid with inline editing. Manually documenting the state management for this would take days. Replay captures the interaction and generates a modern equivalent.

typescript
// Generated by Replay from Legacy Recording #8821
import React, { useState } from 'react';
import { DataGrid, GridColDef } from '@mui/x-charts';

interface LegacyUserRow {
  id: number;
  lastName: string;
  firstName: string;
  accessLevel: string;
}

const UserManagementTable: React.FC<{ data: LegacyUserRow[] }> = ({ data }) => {
  const [rows, setRows] = useState(data);

  // Replay identified the 'Inline Edit' behavior from the video recording
  const handleProcessRowUpdate = (newRow: LegacyUserRow) => {
    const updatedRows = rows.map((row) => (row.id === newRow.id ? newRow : row));
    setRows(updatedRows);
    return newRow;
  };

  return (
    <div className="h-[400px] w-full">
      <DataGrid 
        rows={rows} 
        columns={columns} 
        processRowUpdate={handleProcessRowUpdate}
      />
    </div>
  );
};

This code snippet demonstrates how Replay identifies functional patterns (like inline editing) and maps them to modern libraries (like MUI or Tailwind-based components). You can learn more about this in our Visual Reverse Engineering Guide.

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What are the benefits of a video-first modernization strategy?#

Traditional modernization starts with the "What" (the code). Video-first modernization starts with the "How" (the user experience). This is vital for regulated industries like Healthcare, Financial Services, and Government, where the legacy system's behavior is often legally mandated.

1. •Zero Source Code Dependency: You don't need the original source code to build inventory legacy systems. This is a lifesaver for systems where the source code was lost or the vendor went out of business.
2. •SOC2 and HIPAA Compliance: Replay is built for regulated environments. You can record workflows in a secure environment, and Replay can be deployed On-Premise to ensure data never leaves your network.
3. •Instant Design System: Instead of hiring a design agency to "reimagine" your UI, Replay extracts the existing functional design. You can then apply a "Blueprint" to skin it with modern styles.

Automated Component Extraction#

When Replay processes a video, it populates your "Library." This Library serves as your single source of truth.

tsx
// Replay Component Library: PrimaryButton.tsx
// Extracted from "Mainframe Portal V3"
import React from 'react';

interface ButtonProps {
  label: string;
  onClick: () => void;
  variant: 'primary' | 'secondary';
}

export const LegacyModernizedButton: React.FC<ButtonProps> = ({ label, onClick, variant }) => {
  const baseStyles = "px-4 py-2 rounded font-bold transition-colors";
  const variants = {
    primary: "bg-blue-600 text-white hover:bg-blue-700",
    secondary: "bg-gray-200 text-black hover:bg-gray-300"
  };

  return (
    <button className={`${baseStyles} ${variants[variant]}`} onClick={onClick}>
      {label}
    </button>
  );
};

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

Mainframe systems are notoriously difficult to inventory because the UI (often green-screen terminals) is completely decoupled from the modern web stack. To build inventory legacy systems in a mainframe environment, you record the terminal sessions.

Replay's AI Automation Suite recognizes the text-based layouts and functional triggers of these terminals. It maps "Function Keys" (F1, F2, etc.) to modern UI actions. This allows you to wrap a modern React frontend around a legacy backend without needing to rewrite the COBOL logic on day one.

This "Strangler Fig" pattern is much safer than a "Big Bang" rewrite. You replace the UI first, using Replay to ensure 100% functional parity, then slowly migrate the backend services.

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The Role of AI in UI Inventory#

We are past the era of manual documentation. If your team is still using Excel to build inventory legacy systems, you are wasting capital. Replay is the first platform to use video for code generation, leveraging advanced computer vision to do the heavy lifting.

AI assistants like ChatGPT or Claude are great at writing functions, but they cannot "see" your legacy enterprise software. They don't know that your "Account Balance" field has a specific hover-state behavior that triggers a legacy tooltip. Replay provides the visual context that generic AI lacks.

By recording a session, you provide the AI with the "Visual Context" it needs to generate accurate components. This is why Replay is the only tool that generates component libraries from video with such high fidelity.

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Frequently Asked Questions#

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

Replay (replay.build) is the industry-leading platform for converting video recordings into documented React components and design systems. It is specifically designed for legacy modernization, allowing teams to skip months of manual developer research by using Visual Reverse Engineering to extract UI logic directly from screen recordings.

How do I build inventory legacy systems for a rewrite?#

The most efficient way to build inventory legacy systems is to record user workflows and use an automated tool like Replay to extract components. This eliminates the need for manual code audits and ensures that the inventory is based on actual system behavior. Replay categorizes these into a Library, providing a functional map of every screen and component in the legacy application.

Can I use Replay for systems without source code?#

Yes. Replay is a "black-box" reverse engineering tool. Because it relies on video recordings of the UI, it does not require access to the underlying COBOL, Java, or Delphi source code. This makes it the ideal solution for modernizing abandoned or third-party legacy systems where documentation and source code are unavailable.

Is Replay secure for healthcare or financial data?#

Replay is built for regulated industries. It is SOC2 compliant and HIPAA-ready. For organizations with strict data sovereignty requirements, Replay offers On-Premise deployment options, ensuring that your video recordings and generated code stay within your secure perimeter.

How much time does Replay actually save?#

On average, Replay provides 70% time savings compared to manual modernization methods. While a manual audit and rewrite of a single screen can take 40 hours of developer time, Replay can reduce that to 4 hours by automating the discovery, documentation, and initial code generation phases.

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Ready to modernize without rewriting? Book a pilot with Replay