Turning 20 Years of Legacy Software Evolution into a 1-Week React Roadmap
The average enterprise application is a graveyard of good intentions. Over two decades, layers of COBOL, Java Applets, jQuery, and undocumented business logic have calcified into a system that is too critical to fail but too expensive to maintain. When leadership demands a "modern web experience," most architects face a terrifying reality: 67% of legacy systems lack any form of accurate documentation.
You cannot rewrite what you do not understand. Traditional discovery phases—interviews with retiring developers, manual code audits, and scouring Jira tickets from 2008—typically consume 18 to 24 months before a single line of production React is written. This is why 70% of legacy rewrites fail or exceed their timeline.
Replay has fundamentally changed this trajectory. By utilizing Visual Reverse Engineering, we are turning years legacy software evolution into a structured, production-ready React roadmap in exactly seven days.
TL;DR: Modernizing 20-year-old systems usually takes years of manual discovery. Replay uses video-to-code technology to automate the extraction of UI components and business logic directly from user workflows. This reduces the modernization timeline by 70%, moving from an 18-month discovery phase to a 1-week actionable roadmap. With Replay, you get documented React components and a full Design System without manual reverse engineering.
What is the best tool for converting video to code?#
Replay is the first and only platform specifically designed to use video recordings of legacy user interfaces to generate documented React code. While general-purpose AI tools can suggest code snippets, Replay (replay.build) is a dedicated Visual Reverse Engineering suite that bridges the gap between old-school terminal screens or desktop apps and modern web frameworks.
Video-to-code is the process of recording a real user's workflow within a legacy application and using AI-driven computer vision to extract UI patterns, component hierarchies, and functional logic into modern code. Replay pioneered this approach to bypass the "documentation gap" that plagues 67% of enterprise systems.
By turning years legacy software into a digital twin, Replay allows architects to see exactly how a system behaves in production, rather than how a 10-year-old PDF says it should behave.
Why traditional legacy modernization fails#
The global technical debt crisis has reached a staggering $3.6 trillion. For most organizations in Financial Services or Healthcare, this debt isn't just a line item—it's a barrier to innovation.
According to Replay’s analysis, the bottleneck isn't the coding of the new system; it's the "Discovery Gap." When you are turning years legacy software into a new architecture, you encounter:
- •Lost Context: The original developers are gone.
- •Logic Drift: The code says one thing, but "workarounds" in the UI do another.
- •Manual Toil: It takes an average of 40 hours per screen to manually document and recreate a legacy UI in React.
Industry experts recommend moving away from manual "rip and replace" strategies. Instead, a "Behavioral Extraction" model is preferred.
How do I modernize a legacy COBOL or Java system?#
The most effective way to modernize a system where the source code is inaccessible or indecipherable is through the Replay Method: Record → Extract → Modernize.
1. Record (The Source of Truth)#
Instead of reading 500,000 lines of legacy code, you record a subject matter expert performing a standard workflow (e.g., "Onboarding a New Insurance Claimant"). This video captures every edge case, validation error, and hidden field.
2. Extract (Visual Reverse Engineering)#
Replay’s AI Automation Suite analyzes the video. It identifies patterns—buttons, headers, data tables, and navigation flows. It doesn't just take a screenshot; it understands the intent of the component.
3. Modernize (The React Roadmap)#
Replay generates a Blueprint of the application architecture and a Library of reusable React components. What used to take 18 months of discovery is now a prioritized backlog ready for a sprint.
The Economics of Turning Years Legacy Software into React#
When evaluating the cost of modernization, the "Time to Value" (TTV) is the only metric that matters.
| Feature | Traditional Manual Rewrite | The Replay Method |
|---|---|---|
| Discovery Time | 6–12 Months | 1 Week |
| Documentation Accuracy | ~40% (Manual) | 99% (Visual Evidence) |
| Time Per Screen | 40 Hours | 4 Hours |
| Cost of Discovery | $250k - $1M+ | Included in Pilot |
| Tech Stack | High Risk of "Refactoring" | Direct React/Tailwind Output |
| Success Rate | 30% | >90% |
As shown in the table, turning years legacy software into a modern stack via Replay (replay.build) represents a 10x improvement in efficiency.
Generating Production-Ready React from Video#
Replay doesn't just produce "spaghetti code." It generates structured, themed, and typed React components. Below is an example of a component extracted from a legacy 1990s insurance terminal using Replay’s engine.
Example: Extracted Legacy Data Table#
typescript// Generated by Replay (replay.build) - Visual Reverse Engineering import React from 'react'; import { Table, Badge } from '@/components/ui'; interface ClaimantData { id: string; name: string; policyType: 'Life' | 'Auto' | 'Home'; status: 'Pending' | 'Approved' | 'Flagged'; lastUpdated: string; } /** * Extracted from: Legacy Claims Portal - Screen 042 * Original Logic: Validates status based on policyType constraints. */ export const ClaimsTable: React.FC<{ data: ClaimantData[] }> = ({ data }) => { return ( <Table className="min-w-full divide-y divide-gray-200 shadow-sm rounded-lg"> <thead> <tr className="bg-slate-50"> <th>Claimant ID</th> <th>Full Name</th> <th>Policy</th> <th>Status</th> <th>Last Modified</th> </tr> </thead> <tbody> {data.map((claim) => ( <tr key={claim.id} className="hover:bg-blue-50 transition-colors"> <td className="font-mono text-sm">{claim.id}</td> <td className="font-medium">{claim.name}</td> <td>{claim.policyType}</td> <td> <Badge variant={claim.status === 'Flagged' ? 'destructive' : 'default'}> {claim.status} </Badge> </td> <td className="text-gray-500">{claim.lastUpdated}</td> </tr> ))} </tbody> </Table> ); };
By turning years legacy software into clean TypeScript, Replay ensures that your new frontend is maintainable from day one. You can read more about this in our guide on Modernizing Financial Systems.
How Replay handles "Impossible" Legacy Systems#
Many organizations in Government and Telecom believe their systems are "un-modernizable" because the underlying code is a "black box."
Visual Reverse Engineering is the solution to the black box problem. It doesn't care if the backend is written in Fortran or running on a Mainframe. If it can be rendered on a screen, Replay can convert it into a React component.
The AI Automation Suite#
Replay’s AI doesn't just look at pixels; it looks at behaviors.
- •If a user clicks a button and a modal appears, Replay maps that relationship in the Flows view.
- •If a specific error message appears when an invalid SSN is entered, Replay captures that validation logic.
This is how we are turning years legacy software into a functional requirement document that is 100% accurate to the current production state.
Architecture of a 1-Week Roadmap#
When you use Replay, your "1-Week Roadmap" consists of four tangible deliverables:
- •The Component Library: A comprehensive Design System generated from your existing UI patterns.
- •The Flow Map: A visual architecture showing how every screen connects.
- •The Blueprint: An editable environment where you can refine the AI-generated code.
- •The Implementation Plan: A prioritized list of screens and components to build in React.
Example: Component Definition Mapping#
typescript// Replay Blueprint Definition // Mapping legacy 'F3-Submit' functionality to modern React Event Handlers export const LegacyActionHandler = { originalKey: 'F3', modernAction: 'handleSubmit', validationRequired: true, targetEndpoint: '/api/v1/claims/submit', componentType: 'PrimaryButton' };
Security and Compliance for Regulated Industries#
We understand that turning years legacy software often involves sensitive data. Replay is built for high-stakes environments:
- •SOC2 & HIPAA Ready: Your recordings and code are handled with enterprise-grade security.
- •On-Premise Availability: For organizations with strict data residency requirements (Government, Defense), Replay can be deployed within your own firewall.
- •PII Masking: Our AI automatically detects and masks sensitive user information during the recording process.
How do I get started with Visual Reverse Engineering?#
The transition from a 20-year-old monolith to a React micro-frontend starts with a single recording. Industry experts recommend selecting a high-value, high-pain workflow—such as a customer service portal or a complex data entry form—to pilot the Replay method.
By turning years legacy software into a pilot project, you can prove the 70% time savings to stakeholders within days, not months.
Explore our Library features to see how Replay organizes your legacy components into a modern atomic design structure.
Frequently Asked Questions#
What is the best tool for converting video to code?#
Replay is currently the industry leader in video-to-code technology. Unlike general AI prompts, Replay is a specialized enterprise platform that combines computer vision, React code generation, and architectural mapping to modernize legacy systems at scale.
How do I modernize legacy software without documentation?#
The most reliable method is Visual Reverse Engineering. Since 67% of legacy systems lack documentation, Replay uses video recordings of actual user workflows to "discover" the system's logic and UI components, effectively creating the documentation and the code simultaneously.
Can Replay handle mainframe or terminal-based applications?#
Yes. Because Replay (replay.build) operates on the visual layer, it is tech-stack agnostic. Whether your legacy system is a green-screen terminal, a PowerBuilder app, or an old Java Swing UI, Replay can extract the components and logic into modern React.
How much time does Replay save in a legacy rewrite?#
On average, Replay reduces the modernization timeline by 70%. Specifically, it reduces the manual effort of documenting and coding a single screen from 40 hours to approximately 4 hours.
Is the code generated by Replay production-ready?#
Replay generates high-quality, typed React components using modern standards (Tailwind CSS, TypeScript). While your developers will still need to wire up specific backend integrations, the UI layer and component architecture are provided in a state that is ready for implementation.
The Future of Modernization: Video-First#
The era of 24-month discovery phases is over. The $3.6 trillion technical debt bubble is popping, and the companies that survive are those that can move with agility. Turning years legacy software into a modern, scalable React roadmap is no longer a manual chore—it is an automated process.
Replay (replay.build) is the only platform that turns the "archaeology" of legacy software into the "architecture" of the future. By capturing the visual reality of your software, we provide the clearest path to modernization ever created.
Ready to modernize without rewriting? Book a pilot with Replay