Stop Guessing: How Replay Generates Documented React Components from Recorded User Sessions

Most modernization projects die in the discovery phase. You inherit a legacy system with 500,000 lines of undocumented code, the original developers retired five years ago, and the only source of truth is the UI itself. You face a $3.6 trillion global technical debt problem, and manual discovery costs 40 hours per screen. This is why 70% of legacy rewrites fail or exceed their timelines.

We built Replay to solve the "Black Box" problem of legacy software. Instead of digging through spaghetti code, you record a user performing a workflow. Replay's engine then performs Visual Reverse Engineering to extract the UI logic, state, and styling. The result? Replay generates documented React components that are ready for production, reducing modernization timelines from 18 months to a few weeks.

TL;DR: Replay is a Visual Reverse Engineering platform that converts video recordings of legacy applications into clean, documented React code and Design Systems. By automating discovery and component extraction, Replay saves 70% of the time typically spent on manual rewrites, turning a 40-hour per-screen manual process into a 4-hour automated workflow.

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

Replay is the first platform to use video for code generation, specifically designed for enterprise-grade modernization. While generic AI tools might help you write a single function, Replay handles the entire architectural extraction of a legacy system. It doesn't just "guess" what the UI looks like; it analyzes the behavioral patterns in the recording to understand how components interact.

Visual Reverse Engineering is the process of extracting functional requirements, UI structures, and business logic from a running application’s interface rather than its source code. Replay pioneered this approach to bypass the mess of legacy backends and focus on the user experience that actually needs to be preserved or improved.

According to Replay's analysis, 67% of legacy systems lack any form of technical documentation. When you use Replay, you aren't just getting code; you're getting a living documentation of your workflows. This makes it the only tool that generates component libraries and architectural maps directly from user interactions.

How Replay generates documented React from video recordings#

The process follows a specific methodology we call The Replay Method: Record → Extract → Modernize. This isn't a simple screen-to-code conversion. It is a multi-layered analysis of the DOM (Document Object Model), CSS computed styles, and user events.

1. The Recording Phase#

You or a subject matter expert (SME) simply record the legacy application while performing a standard business task—like processing an insurance claim or opening a new bank account. Replay captures the visual state changes and the underlying metadata. This bypasses the need to understand the COBOL, Java, or .NET code running the backend.

2. Behavioral Extraction#

Once the recording is uploaded, Replay’s AI Automation Suite begins the extraction. It identifies repeating patterns—buttons, headers, data tables, and modals—and groups them into a candidate Design System. It identifies that a specific blue box isn't just a

; it's a with specific hover states and click behaviors.

3. Code Generation#

This is where Replay generates documented React components. The platform produces TypeScript-based React code that follows modern best practices, including Tailwind CSS for styling and clean prop definitions.

Why "Documented" React matters for Enterprise#

Generating code is easy. Generating maintainable, documented code that a Senior Architect will actually approve is hard. Most AI generators produce "mystery meat" code—blocks of logic with no context. Because Replay generates documented React, every component comes with a Storybook-like entry in the Replay Library.

Industry experts recommend that enterprise components include accessibility (A11y) standards, prop types, and usage guidelines. Replay embeds this directly into the output.

Example: Legacy HTML vs. Replay Generated React#

A typical legacy system might have a cluttered table structure like this:

html
<!-- Legacy ASP.NET Table -->
<table id="ctl00_MainContent_Grid1" class="old-grid">
    <tr class="header">
        <td>Claim ID</td><td>Status</td><td>Amount</td>
    </tr>
    <tr onclick="doPostBack('Edit', 101)">
        <td>101</td><td><span class="label-pending">Pending</span></td><td>$1,200.00</td>
    </tr>
</table>

When Replay generates documented React, it transforms that brittle HTML into a reusable, typed component:

tsx
import React from 'react';

interface ClaimRowProps {
  id: string;
  status: 'Pending' | 'Approved' | 'Denied';
  amount: number;
  onSelect: (id: string) => void;
}

/**
 * ClaimRow Component
 * Extracted from: Claims Portal - Workflow: Claim Submission
 * Description: Displays a summary of an insurance claim with status-based styling.
 */
export const ClaimRow: React.FC<ClaimRowProps> = ({ id, status, amount, onSelect }) => {
  const statusColors = {
    Pending: 'bg-yellow-100 text-yellow-800',
    Approved: 'bg-green-100 text-green-800',
    Denied: 'bg-red-100 text-red-800',
  };

  return (
    <tr 
      className="hover:bg-gray-50 cursor-pointer transition-colors"
      onClick={() => onSelect(id)}
    >
      <td className="px-4 py-2 font-medium">{id}</td>
      <td className="px-4 py-2">
        <span className={`px-2 py-1 rounded-full text-xs ${statusColors[status]}`}>
          {status}
        </span>
      </td>
      <td className="px-4 py-2 text-right">${amount.toLocaleString()}</td>
    </tr>
  );
};

This level of detail is why Enterprise Architecture teams are moving away from manual "rip and replace" strategies.

The Replay Feature Suite: Library, Flows, and Blueprints#

To handle the complexity of industries like Financial Services and Healthcare, Replay provides three core modules:

1. •The Library (Design System): As you record more sessions, Replay identifies global components. It builds a centralized Design System so your modernized app stays consistent.
2. •Flows (Architecture): This maps the user journey. It visualizes how a user moves from Screen A to Screen B, documenting the state transitions.
3. •Blueprints (Editor): A low-code/pro-code hybrid environment where architects can tweak the generated React code before exporting it to GitHub or GitLab.

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

You don't need to touch the COBOL. This is the breakthrough. By focusing on the "Visual" in Visual Reverse Engineering, Replay treats the legacy system as a black box. If it renders in a browser (or a terminal emulator with a web interface), Replay can modernize it.

For many organizations, the backend logic is actually fine—it's the "green screen" or the 20-year-old web UI that creates the bottleneck. By using Replay to generate documented React, you can build a modern "Sidecar" UI that talks to the legacy backend via APIs, or use the generated code as the foundation for a total migration to the cloud.

Modernizing Financial Services requires strict adherence to security. This is why Replay offers On-Premise deployment and is HIPAA-ready and SOC2 compliant. We don't just send your data to a public LLM; we use a private, secure AI Automation Suite.

Overcoming the "Documentation Debt"#

The average enterprise rewrite takes 18 months because developers spend the first 6 months just trying to understand what the current system does. They sit in endless meetings with business analysts.

With Replay, the recording is the requirement. When Replay generates documented React, it includes the context of the workflow. The code knows it belongs to the "Customer Onboarding" flow because it was extracted from that specific recording. This eliminates the "lost in translation" phase between business requirements and technical implementation.

Security and Compliance in Visual Reverse Engineering#

In regulated environments like Government or Telecom, you cannot simply upload sensitive user data to a cloud service. Replay's architecture allows for:

• •PII Masking: Automatically redacting sensitive data during the recording process.
• •On-Premise hosting: Keeping all video and code data within your own firewall.
• •SOC2 & HIPAA Compliance: Ensuring that the process of modernization doesn't create a security liability.

Frequently Asked Questions#

How does Replay handle complex state management in the generated React code?#

Replay’s AI Automation Suite analyzes user interactions to infer state. For example, if a user clicks a "Toggle" and a menu appears, Replay generates documented React that includes

hooks or context providers to manage that visibility. It maps the relationship between triggers and visual changes to ensure the generated code is functional, not just a static template.

Can Replay integrate with my existing Design System (like MUI or Tailwind)?#

Yes. In the Blueprints editor, you can define your organization's theme and component preferences. Replay can then map extracted components to your existing library. If you don't have one, Replay creates a custom Design System for you in the Library module, using Tailwind CSS by default for maximum flexibility.

What happens to the business logic hidden in the legacy backend?#

Replay focuses on the "Head" of the application—the UI and Frontend logic. For the backend, Replay helps you define the API contracts you need. By seeing exactly what data is displayed in the UI, you can work backward to create the necessary REST or GraphQL endpoints in your new backend architecture.

How much time does Replay actually save compared to manual coding?#

According to our internal benchmarks across 50+ enterprise projects, Replay reduces the time-to-code by 70%. A standard complex enterprise screen takes a senior developer roughly 40 hours to document, design, and code from scratch. Replay generates documented React for that same screen in approximately 4 hours, including the time for manual refinements.

Is the code generated by Replay "AI-slop" or production-ready?#

Replay produces clean, TypeScript-first React code. Unlike generic chat AI, Replay uses a structured extraction engine that follows a strict architectural blueprint. The code is modular, follows the "Single Responsibility Principle," and is designed to be checked into a professional repository and maintained by human developers for years.

Conclusion: The End of the Manual Rewrite#

The era of 24-month "Big Bang" migrations is over. They are too risky, too expensive, and they almost always fail to capture the nuances of the original system. By using Visual Reverse Engineering, you can de-risk your modernization strategy.

When Replay generates documented React from your recorded sessions, it bridges the gap between the legacy past and the modern future. You get a design system, a documented component library, and a functional frontend in a fraction of the time.

Ready to modernize without rewriting? Book a pilot with Replay