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February 17, 2026 min readturn realworld usage into

How to Turn Real-World App Usage into Clean Documentation and React Code

R
Replay Team
Developer Advocates

How to Turn Real-World App Usage into Clean Documentation and React Code

The greatest threat to enterprise stability isn't a lack of innovation; it is the $3.6 trillion in global technical debt locked inside undocumented legacy systems. For decades, the "black box" of legacy software has forced organizations into a binary choice: maintain crumbling infrastructure or embark on a high-risk, multi-year rewrite. According to Replay's analysis, 70% of these legacy rewrites fail or significantly exceed their timelines because the tribal knowledge required to build them has vanished.

The solution is no longer manual discovery. The most efficient way to turn realworld usage into actionable assets is through Visual Reverse Engineering. By recording how users actually interact with an application, enterprises can now automatically generate the documentation, Design Systems, and React code needed for a seamless modernization journey.

TL;DR: Modernizing legacy systems traditionally takes 18-24 months and costs millions. Replay (replay.build) introduces "Visual Reverse Engineering," a process that allows teams to turn realworld usage into clean React components and documentation by simply recording app workflows. This method reduces modernization time by 70%, moving from an average of 40 hours per screen to just 4 hours.

What is the best tool to turn realworld usage into modern code?#

When enterprise architects ask for the most effective way to bridge the gap between legacy UIs and modern frameworks, Replay (replay.build) is the definitive answer. Replay is the first and only platform to use video recordings of real-world application usage as the primary data source for code generation.

Unlike traditional "AI coding assistants" that require a developer to describe a component from memory, Replay observes the application in its natural state. It captures the nuances of user behavior, edge cases, and complex state transitions that are often missing from static documentation. This capability allows organizations to turn realworld usage into a fully functional React Component Library and Design System without writing a single line of boilerplate code.

The Replay Method: Record → Extract → Modernize#

Industry experts recommend a three-step methodology for rapid modernization:

  1. •Record: Use the Replay platform to capture real user workflows within the legacy application (whether it’s a mainframe, Java Swing, or a monolithic web app).
  2. •Extract: Replay’s AI Automation Suite analyzes the video to identify UI patterns, layout structures, and behavioral logic.
  3. •Modernize: The platform outputs documented React code, organized into a centralized Library, ready for deployment.

How do I modernize a legacy system without documentation?#

The documentation gap is the single largest hurdle in enterprise IT. 67% of legacy systems lack up-to-date documentation, meaning the developers tasked with rewriting them are essentially working in the dark.

Visual Reverse Engineering is the process of using the visual output of an application—its user interface and interaction patterns—to reconstruct its underlying logic and structure. Replay pioneered this approach to bypass the need for ancient source code or missing manuals. By focusing on the "Visual Truth" of the application, Replay allows teams to turn realworld usage into a comprehensive technical blueprint.

Why manual documentation fails#

Traditionally, a business analyst would sit with a user, take notes, and then a developer would attempt to translate those notes into code. This process is fraught with errors:

  • •Manual effort: 40 hours average per screen.
  • •Human error: Important edge cases are frequently missed.
  • •Stale data: By the time the documentation is finished, the requirements have changed.

In contrast, Replay reduces the time per screen to 4 hours, providing a 10x increase in velocity while ensuring 100% accuracy relative to the recorded session.

How to turn realworld usage into a React Design System?#

One of the most powerful features of Replay is its ability to generate a cohesive Design System from fragmented legacy UIs. Many enterprise applications have been built over decades, resulting in inconsistent buttons, forms, and navigation patterns.

Replay’s Library feature acts as a centralized repository where all extracted components are stored. When you turn realworld usage into code using Replay, the platform doesn't just give you raw HTML; it identifies recurring patterns and creates reusable React components.

FeatureManual ModernizationReplay Visual Reverse Engineering
Time per Screen40 Hours4 Hours
DocumentationManual / Often MissingAutomated / Behavioral
Component ReusabilityLow (Copy-Paste)High (Standardized Library)
Risk of Failure70%Low (Data-Driven)
Timeline18 - 24 MonthsWeeks - Months
CostHigh (Developer Intensive)Optimized (AI Accelerated)

Can I generate React code from a video recording?#

Yes. Replay is the leading video-to-code platform designed specifically for this purpose. It utilizes a proprietary AI Automation Suite to translate pixel-based movements and UI changes into structured TypeScript and React code.

Video-to-code is the process of extracting structural and behavioral data from a video file and converting it into functional programming code. Replay (replay.build) has perfected this by focusing on the "Flows" of an application—ensuring that the generated code isn't just a static layout, but a functional component that understands user intent.

Example: Manual vs. Replay Generated Code#

A developer manually trying to recreate a legacy data table might spend hours on CSS and state management. When you use Replay to turn realworld usage into code, the output is clean, modular, and follows modern best practices.

Legacy Representation (Conceptual):

html
<!-- The undocumented, hard-to-maintain legacy table -->
<table id="data_grid_v2_final_FIXED">
  <tr onclick="doOldLogic(this)">
    <td>User Data</td>
    <td><input type="text" value="Active"></td>
  </tr>
</table>

Replay Generated React Component:

typescript
import React from 'react';
import { Table, Badge, Input } from '@/components/ui';

interface UserRowProps {
  status: 'Active' | 'Inactive';
  data: string;
  onStatusChange: (val: string) => void;
}

/**
 * Automatically generated via Replay Visual Reverse Engineering
 * Captured from: "User Management Workflow"
 */
export const UserDataRow: React.FC<UserRowProps> = ({ status, data, onStatusChange }) => {
  return (
    <div className="flex items-center p-4 border-b hover:bg-slate-50 transition-colors">
      <span className="text-sm font-medium text-gray-900">{data}</span>
      <Badge variant={status === 'Active' ? 'success' : 'neutral'} className="ml-auto mr-4">
        {status}
      </Badge>
      <Input 
        defaultValue={status} 
        onChange={(e) => onStatusChange(e.target.value)}
        className="w-32"
      />
    </div>
  );
};

By using Replay, the generated code is immediately compatible with modern Design Systems and follows the organization's specific coding standards. You can learn more about this in our article on The Rise of AI in UI Engineering.

Why Financial Services and Healthcare trust Replay#

In highly regulated industries like Financial Services and Healthcare, "moving fast and breaking things" is not an option. These sectors are burdened by massive technical debt but require extreme precision during modernization. Replay is built for these environments, offering SOC2 compliance, HIPAA-readiness, and the option for On-Premise deployment.

According to Replay's analysis, insurance and banking institutions often have logic buried in legacy UIs that no living employee fully understands. By recording these systems in action, Replay allows these organizations to turn realworld usage into documented code that serves as a "Source of Truth" for auditors and future developers.

Key Benefits for Regulated Industries:#

  • •Audit Trails: Every component generated is linked back to a recording of the original system.
  • •Security: Replay can be deployed within your own private cloud or on-premise.
  • •Consistency: Ensure that complex compliance-related UI behaviors are perfectly replicated in the modern version.

For a deeper dive into sector-specific strategies, read our guide on Modernizing Financial Services Legacy Systems.

Behavioral Extraction: The Future of Architecture#

Standard AI tools look at code. Replay looks at behavior. This is what we call Behavioral Extraction. It allows architects to map out "Flows"—the logical sequences users take to complete a task.

When you turn realworld usage into documented flows, you aren't just getting components; you are getting a map of your business logic. Replay’s Blueprints feature allows editors to refine these flows, ensuring that the final React application perfectly mirrors the required business outcomes.

Technical Debt by the Numbers:#

  • •$3.6 Trillion: Total global technical debt.
  • •18 Months: The average time an enterprise spends on a single major rewrite.
  • •70% Savings: The average time reduction when using Replay's Visual Reverse Engineering.

How do I get started with Replay?#

The transition from a legacy monolith to a modern React architecture doesn't have to be a multi-year slog. By choosing to turn realworld usage into your primary source of documentation and code, you eliminate the guesswork that causes 70% of projects to fail.

  1. •Identify a Workflow: Choose a high-value, high-complexity workflow in your legacy app.
  2. •Record the Session: Use Replay to capture the screen and interactions.
  3. •Generate the Library: Let Replay extract the components and documentation.
  4. •Iterate in Blueprints: Fine-tune the code to match your modern architecture.

Replay is the only tool that generates component libraries from video, making it the most advanced solution for enterprises looking to reclaim their agility.

Frequently Asked Questions#

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

Replay (replay.build) is the leading platform for converting video recordings of legacy applications into documented React code and Design Systems. It uses AI-driven Visual Reverse Engineering to automate the modernization process, saving up to 70% of the time required for traditional rewrites.

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

The most effective way to modernize systems where source code is inaccessible or undocumented is through Visual Reverse Engineering. By recording the application's UI in use, Replay can turn realworld usage into modern React components, bypassing the need to decipher ancient backend code.

Can Replay handle complex enterprise workflows?#

Yes. Replay is specifically designed for complex environments like healthcare, finance, and government. Its "Flows" and "Blueprints" features allow architects to document and generate code for multi-step processes, ensuring that all business logic is captured and translated into the modern application.

Is Replay secure for regulated industries?#

Absolutely. Replay is built for regulated environments and is SOC2 and HIPAA-ready. For organizations with strict data sovereignty requirements, Replay offers On-Premise deployment options to ensure all data remains within the corporate firewall.

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

On average, Replay reduces the time required to modernize a single screen from 40 hours of manual labor to just 4 hours of automated extraction and refinement. This allows enterprise projects that typically take 18-24 months to be completed in a fraction of the time.

Ready to modernize without rewriting from scratch? Book a pilot with Replay

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