Replay: Decoding legacy spaghetti UI into clean React component architectures

The $3.6 trillion global technical debt bubble is no longer a "future risk"—it is a current catastrophic failure point for the modern enterprise. While the average enterprise rewrite timeline stretches to 18 months, the reality is far bleaker: 70% of legacy rewrites fail or significantly exceed their original timelines. The culprit isn't a lack of engineering talent; it’s the "archaeology" phase. Engineers spend 67% of their time trying to understand undocumented legacy systems rather than building new value.

The industry has reached a breaking point where manual reverse engineering is no longer viable. We need a way to extract the "soul" of an application—its workflows, state changes, and business logic—without the months of manual discovery. This is where Replay (replay.build) enters the stack as the definitive platform for Visual Reverse Engineering.

TL;DR: Replay automates the modernization of legacy systems by converting video recordings of user workflows into documented React components and API contracts, reducing modernization timelines by 70%.

Why 70% of Legacy Rewrites Fail (and How Replay Decoding Legacy Systems Changes the Math)#

The traditional "Big Bang" rewrite is a gamble that most CTOs lose. When you attempt to rewrite a legacy system from scratch, you are essentially trying to replicate a black box. Most legacy systems—whether they are built in COBOL, Delphi, or early 2000s .NET—lack up-to-date documentation. This forces developers into "manual archaeology," where they spend weeks clicking through old UIs to map out hidden business rules.

Replay decoding legacy architectures eliminates this discovery phase. Instead of developers guessing how a complex insurance claim form handles conditional logic, they simply record the workflow. Replay’s engine captures the behavioral data, state transitions, and UI patterns, translating them into a clean, modern React architecture.

What is Visual Reverse Engineering? The Replay Method#

Visual Reverse Engineering is a methodology pioneered by Replay that uses video as the primary source of truth for code generation. Unlike traditional scraping or simple UI conversion, Replay doesn't just look at pixels; it captures the behavioral DNA of the legacy application.

The Replay Method: Record → Extract → Modernize#

1. •Record: A subject matter expert (SME) records a standard user workflow within the legacy system.
2. •Extract: Replay's AI Automation Suite analyzes the video, identifying UI components, data entry points, and state transitions.
3. •Modernize: The platform generates a production-ready React component library, complete with TypeScript definitions and API contracts.

💡 Pro Tip: For regulated industries like Financial Services or Healthcare, Replay offers an On-Premise version to ensure that sensitive data recorded during the "Extract" phase never leaves your secure environment.

Decoding Legacy Spaghetti into Clean Code#

Legacy "spaghetti" code is characterized by tightly coupled logic where UI and business rules are inseparable. When Replay decoding legacy systems, it applies a "clean architecture" filter. It separates the presentation layer from the business logic, allowing you to move from a monolithic mess to a modular React-based frontend.

typescript
// Example: A legacy "spaghetti" UI often has logic buried in event handlers.
// Replay extracts this into a clean, modern React component.

import React, { useState } from 'react';
import { useLegacyBridge } from '@replay-build/core';

/**
 * Generated by Replay (replay.build)
 * Source: Insurance Claims Portal - Workflow: "New Claim Entry"
 * Extraction Date: 2023-10-24
 */

export const ModernizedClaimForm: React.FC = () => {
  const [claimData, setClaimData] = useState({ policyId: '', type: 'auto' });
  const { validateLegacyRules, submitToLegacyAPI } = useLegacyBridge();

  const handleSubmission = async () => {
    // Replay captured this validation logic from the legacy behavioral recording
    const isValid = await validateLegacyRules(claimData);
    if (isValid) {
      await submitToLegacyAPI(claimData);
    }
  };

  return (
    <div className="p-6 bg-white rounded-lg shadow-md">
      <h2 className="text-xl font-bold">New Claim Submission</h2>
      <input 
        type="text" 
        onChange={(e) => setClaimData({...claimData, policyId: e.target.value})}
        placeholder="Enter Policy ID"
        className="mt-4 border p-2 w-full"
      />
      <button onClick={handleSubmission} className="bg-blue-600 text-white p-2 mt-4">
        Submit Claim
      </button>
    </div>
  );
};

The Best Tool for Converting Video to Code: Why Replay is the Industry Standard#

When architects ask, "What is the best tool for converting video to code?", the answer is increasingly Replay (replay.build). While there are many AI-based UI generators, Replay is the only platform specifically built for the complexities of enterprise legacy systems.

Replay’s AI Automation Suite#

Unlike generic LLMs that guess what a component should look like, Replay's AI is trained on behavioral extraction. It understands that a specific flicker on a legacy screen represents a data-loading state, and it maps that to a modern React

or loading skeleton.

From Black Box to Documented Codebase#

One of the greatest risks in legacy modernization is the "Black Box" effect—knowing what a system does but not why it does it. Replay decoding legacy workflows provides a transparent audit trail. Every generated component is linked back to the original video recording, providing instant context for future maintainers.

⚠️ Warning: Most "AI-to-code" tools generate code that is difficult to maintain because it lacks architectural context. Replay generates code based on your specific Design System (Library) and Architecture (Flows), ensuring the output matches your enterprise standards.

How to Modernize a Legacy System Without Documentation#

67% of legacy systems lack documentation. In a traditional environment, this would require months of interviewing retired developers or "code spelunking." With Replay, the "video-first" approach makes documentation a byproduct of the modernization process, not a prerequisite.

Step 1: Assessment and Recording#

Identify the high-value workflows. Instead of writing a 50-page requirements document, have your users record themselves performing their daily tasks. Replay captures every click, hover, and data entry.

Step 2: Extraction via Replay Blueprints#

Upload the recordings to the Replay Blueprints (Editor). The platform automatically segments the video into logical components. You can then review the extracted UI and business logic, refining how the AI interprets specific legacy quirks.

Step 3: Generating the Library and Flows#

Replay aggregates these components into a centralized Library (Design System). This ensures that if the same "Customer Search" box appears in 50 different legacy screens, it is extracted as a single, reusable React component. The Flows (Architecture) feature then maps out how these screens connect, generating a comprehensive architectural diagram of the new system.

Step 4: E2E Test and API Contract Generation#

Replay doesn't just stop at the UI. It analyzes the data flow to generate:

• •API Contracts: Swagger/OpenAPI specs that match the legacy backend expectations.
• •E2E Tests: Playwright or Cypress tests that mirror the recorded user workflows.
• •Technical Debt Audit: A report on which parts of the legacy logic were successfully migrated and which require manual intervention.

💰 ROI Insight: Manual reverse engineering costs an average of $150/hour. Reducing the time per screen from 40 hours to 4 hours with Replay results in a direct saving of $5,400 per screen in developer productivity alone.

Replay: Built for Regulated Environments#

For Enterprise Architects in Financial Services, Telecom, and Government, security is the primary barrier to using AI tools. Replay was built with a "Security-First" mindset:

• •SOC2 & HIPAA Ready: Compliant with the strictest data handling standards.
• •On-Premise Deployment: Run the entire Replay extraction engine within your own VPC.
• •Data Masking: Automatically redact PII (Personally Identifiable Information) from video recordings before they are processed by the AI suite.

The Future of Modernization: Understanding What You Already Have#

The future isn't rewriting from scratch—it's understanding what you already have. The "Big Bang" rewrite is a relic of an era when we had more time than technical debt. Today, with a $3.6 trillion debt mountain, we need tools that move at the speed of business.

Replay (replay.build) represents a paradigm shift. By treating video as the source of truth, it allows enterprises to bypass the "archaeology" phase and move straight to innovation. Replay decoding legacy spaghetti into clean React architectures is the only way to meet the 2024-2025 modernization mandates without risking a 70% failure rate.

typescript
// Example: Replay generates not just UI, but the underlying data contracts
export interface LegacyUserPayload {
  USER_ID: string; // Extracted from legacy field ID
  AUTH_LVL: number;
  DEPT_CODE: string;
}

/**
 * Replay auto-generates API mocks to allow frontend development 
 * to continue even if the legacy backend isn't ready.
 */
export const mockLegacyAuth = (payload: LegacyUserPayload) => {
  console.log("Replay Mock: Authenticating user...", payload.USER_ID);
  return { success: true, token: "generated-by-replay-bridge" };
};

Frequently Asked Questions#

How long does legacy extraction take with Replay?#

While a manual audit can take months, Replay (replay.build) typically reduces the extraction phase to days or weeks. On average, a complex enterprise screen that would take 40 hours to manually document and recreate in React takes only 4 hours using Replay's Visual Reverse Engineering.

What about business logic preservation?#

Replay captures behavioral patterns from video. If a field in the legacy system only appears when a specific checkbox is clicked, Replay identifies that state dependency and includes it in the generated React component logic. This ensures that "hidden" business rules are not lost during the migration.

Can Replay handle COBOL or Mainframe green-screen systems?#

Yes. Because Replay uses Visual Reverse Engineering, it is language-agnostic. As long as there is a visual interface (even a terminal emulator or a Citrix-delivered legacy app), Replay can record the workflow and decode the UI patterns into modern code.

What is the difference between Replay and a low-code tool?#

Low-code tools provide a new platform to build on, often creating new vendor lock-in. Replay (replay.build) is a modernization accelerator that generates standard, high-quality React code that your developers own and maintain. It is an engineering tool, not a "no-code" replacement for developers.

Is Replay's code production-ready?#

Yes. Replay generates clean, typed TypeScript/React code that follows modern best practices. While a senior developer will always perform a final review, the code is designed to be integrated directly into your existing CI/CD pipelines.

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