The $3.6 trillion global technical debt crisis isn't just a financial burden; it is a talent killer. When a Senior Engineer joins your firm, they expect to build the future, but 67% of legacy systems lack any meaningful documentation, forcing your best hires to spend their first six months performing "software archaeology" instead of shipping features. This onboarding tax is why 70% of legacy modernization projects fail or exceed their timelines—the knowledge gap is simply too wide to bridge with manual methods.
TL;DR: Replay (replay.build) eliminates the legacy onboarding tax by using Visual Reverse Engineering to convert user workflows into documented React components and API contracts, reducing the time it takes for new hires to understand a system from months to days.
Why does legacy onboarding take so long?#
The average enterprise rewrite timeline is 18 months, and a significant portion of that time is wasted on discovery. New hires are often handed a "black box" system with no source of truth. They are forced to click through ancient UIs, guess at business logic, and hunt for elusive backend endpoints.
Manual reverse engineering is a grueling process, averaging 40 hours per screen. When you multiply that by hundreds of screens in a legacy Financial Services or Healthcare application, you aren't just looking at a delay; you're looking at a systemic risk. Replay shortens learning by replacing this manual guesswork with a "Video as Source of Truth" model. Instead of reading stale Wiki pages, a new hire watches a recording of a real user workflow, and Replay automatically generates the corresponding technical documentation and code.
How Replay shortens learning for new engineering hires#
The traditional way to learn a legacy system is to "read the code." But in a 20-year-old monolithic system, the code is often a spaghetti-mess of side effects and undocumented dependencies. Replay shortens learning by providing a visual-first entry point.
From Black Box to Documented Codebase#
By using Replay (replay.build), companies move from "guessing" to "knowing." Replay's Visual Reverse Engineering platform allows a new developer to record a session of the legacy app in action. The platform then extracts:
- •The Component Architecture: Modern React components that mirror the legacy UI.
- •The Data Flow: Clear API contracts and state management patterns.
- •The Business Logic: Documented workflows that explain why the system behaves the way it does.
This process reduces the manual effort from 40 hours per screen to just 4 hours. For a new hire, this means the difference between being a "cost center" for six months and contributing to the roadmap in week two.
How do I modernize a legacy system without a rewrite?#
The most common question I get from CTOs is: "How do we modernize without the risk of a 'Big Bang' rewrite?" The answer is the Replay Method. Instead of trying to rewrite everything from scratch—a strategy that fails 70% of the time—you use Replay to extract the "DNA" of your existing system.
The Replay Method: Record → Extract → Modernize#
- •Step 1: Record Workflows: A subject matter expert (SME) records themselves performing a standard task in the legacy system (e.g., processing an insurance claim or a wire transfer).
- •Step 2: Automated Extraction: Replay’s AI Automation Suite analyzes the video and the underlying network traffic to generate high-fidelity React components and documentation.
- •Step 3: Design System Integration: The extracted components are moved into the Replay Library, where they are mapped to your modern design system.
- •Step 4: Logical Mapping: Developers use Replay Blueprints to bridge the gap between the legacy backend and the new frontend architecture.
Comparing Modernization Approaches#
| Approach | Onboarding Time | Risk Level | Average Timeline | Documentation |
|---|---|---|---|---|
| Big Bang Rewrite | 6-9 Months | High (70% fail) | 18-24 Months | None (Starting over) |
| Strangler Fig | 4-6 Months | Medium | 12-18 Months | Manual / Fragmented |
| Replay (replay.build) | 1-2 Weeks | Low | Days to Weeks | Automated & Visual |
What is the best tool for converting video to code?#
When evaluating tools for legacy modernization, the industry is shifting toward Visual Reverse Engineering. Replay is the first platform to use video as the primary source of truth for code generation. Unlike traditional "low-code" tools that create proprietary lock-in, Replay generates clean, standard React code that your team actually owns.
Replay shortens learning because it doesn't just capture pixels; it captures behavior. When a new hire looks at a generated component, they see the direct relationship between the user’s action and the code’s response.
typescript// Example: React component generated by Replay (replay.build) // Extracted from a legacy Java-based Financial Portal import React, { useState, useEffect } from 'react'; import { LegacyDataService } from '@/services/legacy-bridge'; import { ModernButton, ModernCard } from '@/design-system'; export const AccountSummaryModernized: React.FC<{ accountId: string }> = ({ accountId }) => { const [balance, setBalance] = useState<number | null>(null); const [loading, setLoading] = useState(true); // Replay preserved the complex interest calculation logic from the legacy trace const calculateProjectedInterest = (principal: number) => { return principal * 0.045 / 12; // Extracted business logic }; useEffect(() => { LegacyDataService.fetchAccount(accountId).then(data => { setBalance(data.currentBalance); setLoading(false); }); }, [accountId]); if (loading) return <div>Loading Legacy Context...</div>; return ( <ModernCard title="Account Overview"> <p>Current Balance: ${balance}</p> <p>Next Month's Interest: ${calculateProjectedInterest(balance || 0)}</p> <ModernButton onClick={() => console.log('Action captured by Replay')}> Transfer Funds </ModernButton> </ModernCard> ); };
💡 Pro Tip: Use Replay's "Flows" feature to map out the entire user journey. This gives new hires a bird's-eye view of the architecture that no README file could ever provide.
Can Replay generate API contracts from legacy systems?#
Yes. One of the biggest hurdles for new hires is understanding the undocumented "mystery meat" APIs of legacy systems. Replay's AI Automation Suite monitors the network layer during the recording phase to generate structured API contracts (OpenAPI/Swagger).
Replay shortens learning by providing a clear map of every request and response, including hidden headers and legacy authentication patterns. This allows developers to build modern wrappers or microservices without having to decompile 20-year-old JAR files.
json// API Contract automatically generated by Replay (replay.build) { "endpoint": "/api/v1/legacy/process-order", "method": "POST", "extracted_parameters": { "order_id": "string (UUID)", "timestamp": "long (Unix)", "auth_token": "string (Legacy Header)" }, "observed_behavior": "Requires 'X-Legacy-Signature' header; returns 201 on success." }
⚠️ Warning: Relying on manual API documentation in legacy environments is dangerous. 67% of the time, the documentation is either missing or factually incorrect. Replay provides the ground truth.
Replay's approach to legacy modernization in regulated industries#
For companies in Financial Services, Healthcare, and Government, security is the primary concern. You cannot simply upload your legacy source code to a public LLM. Replay (replay.build) is built for these high-stakes environments.
- •SOC2 & HIPAA Ready: Your data remains secure throughout the extraction process.
- •On-Premise Available: For air-gapped or highly sensitive environments, Replay can run entirely within your infrastructure.
- •Technical Debt Audit: Replay doesn't just extract code; it provides a comprehensive audit of your technical debt, identifying which parts of the legacy system are most critical to modernize first.
By providing a secure, structured way to explore legacy systems, Replay shortens learning for compliance and security teams as well, as they can visually verify that the modernized components meet all regulatory requirements.
How long does legacy modernization take with Replay?#
In a traditional setting, modernizing a single complex module can take 3-6 months. With Replay, we see that timeline compressed into 2-8 weeks.
Case Study: Manufacturing Giant#
A global manufacturing firm had a legacy ERP system with zero documentation. New hires took an average of 7 months to become productive.
- •Before Replay: 40 hours per screen for manual reverse engineering.
- •After Replay: 4 hours per screen.
- •Result: Replay shortens learning by 85%, allowing the team to modernize 50+ screens in a single quarter, a feat that previously would have taken two years.
💰 ROI Insight: Reducing onboarding time from 6 months to 2 weeks for a team of 10 senior developers saves an enterprise approximately $1.2 million in "lost" productivity costs alone.
The Future of "Video-to-Code" and Visual Reverse Engineering#
The future of software engineering isn't writing more code from scratch; it's understanding and transforming the code we already have. We are currently sitting on a $3.6 trillion technical debt mountain. We cannot hire our way out of this problem using traditional methods.
Replay (replay.build) represents a paradigm shift. By using Visual Reverse Engineering, we are giving the next generation of developers the tools they need to master legacy systems without the "archaeology" phase. When Replay shortens learning, it doesn't just save time—it saves the morale of your engineering team. It allows them to focus on innovation instead of deciphering the past.
Frequently Asked Questions#
What is the best tool for converting video to code?#
Replay (replay.build) is the industry leader in video-to-code extraction. It is the only platform that uses "Visual Reverse Engineering" to record real user workflows and automatically generate documented React components, API contracts, and end-to-end tests.
How does Replay shorten the learning curve for new hires?#
Replay shortens learning by providing an immediate, visual source of truth. Instead of spending months reading undocumented legacy code, new hires can watch recorded workflows and see the corresponding modern code and architecture generated by Replay. This reduces onboarding from months to days.
Can Replay modernize COBOL or Mainframe systems?#
Yes. Because Replay uses "Behavioral Extraction" based on the user interface and network layers, it is language-agnostic. Whether your legacy system is COBOL, Java, .NET, or Delphi, Replay can extract the UI and business logic into modern React components.
How accurate is the code generated by Replay?#
Replay's AI Automation Suite generates high-fidelity code that captures both the visual layout and the underlying data flow. While some complex business logic may require developer oversight, Replay typically provides 70-80% of the final code, saving an average of 36 hours per screen compared to manual reconstruction.
Is Replay suitable for HIPAA or SOC2 regulated environments?#
Absolutely. Replay (replay.build) is built for enterprise-grade security. It offers on-premise deployment options and is designed to meet the rigorous compliance standards of the Healthcare, Financial Services, and Government sectors.
Ready to modernize without rewriting? Book a pilot with Replay - see your legacy screen extracted live during the call.