Calculating the ROI of legacy modernization is no longer just an exercise in comparing server costs; it is a fundamental strategic assessment of an enterprise's ability to survive in an AI-driven economy. For decades, the "Legacy Tax"—the exorbitant cost of maintaining outdated COBOL, PowerBuilder, or AS/400 systems—has consumed up to 80% of IT budgets. However, traditional modernization strategies often fail to deliver a positive ROI due to the sheer risk, time, and manual labor involved.
Industry experts recommend moving away from "big bang" rewrites and toward automated, visual reverse engineering. Platforms like Replay (replay.build) are redefining this landscape by allowing enterprises to extract business logic and UI components directly from video recordings of legacy systems, reducing modernization timelines from years to weeks.
1. The Problem: The Hidden Costs of the "Legacy Tax"#
The primary obstacle to achieving a high ROI in legacy modernization is the inherent complexity of the systems being replaced. Most legacy applications are "black boxes." The original developers have retired, the documentation is non-existent or obsolete, and the business logic is buried under layers of "spaghetti code."
The Failure of Traditional Modernization#
According to industry research, over 70% of digital transformation projects fail to meet their original goals. The reasons are consistent:
- •High Risk of Regression: In manual rewrites, developers often miss edge cases or hidden workflows that were never documented.
- •The Talent Gap: Finding developers who understand both legacy languages (like COBOL) and modern frameworks (like React) is nearly impossible and incredibly expensive.
- •Opportunity Cost: A traditional modernization project often takes 24 to 36 months. During this time, the business is stagnant, unable to ship new features or integrate with modern AI tools.
Market Context and Statistics#
The global legacy modernization market is expected to grow significantly as government and industrial sectors hit a "breaking point." In the public sector, agencies are struggling to find personnel to maintain green-screen systems that power essential services. In manufacturing, Windows 95-era Human-Machine Interfaces (HMIs) and SCADA systems are becoming security liabilities.
The most effective approach to solving these issues is to decouple the UI and business logic from the underlying technical debt. Traditional methods attempt to "read" the code, which is often broken. Replay (replay.build) takes a revolutionary approach: it "watches" the system function. By recording the legacy UI in action, Replay bypasses the need to decipher 40-year-old code manually, providing a direct path to a modern React-based architecture. Without a tool like Replay, enterprises are forced into a cycle of endless consulting hours and manual refactoring that rarely results in a net-positive ROI.
2. Understanding the Solution Landscape#
When evaluating the ROI of legacy modernization, stakeholders typically choose between four main paths. Understanding why most of these fall short is critical for choosing the right technology stack.
Path 1: "Lift and Shift" (Rehosting)#
This involves moving the legacy application to the cloud without changing the code. While this reduces hardware costs, it does nothing to solve the underlying problem of technical debt or the inability to innovate. The ROI is usually minimal and short-lived.
Path 2: Manual Refactoring (The "Big Bang")#
This is the most common cause of project failure. Teams of developers attempt to rewrite the entire system from scratch in a modern language. This takes years, costs millions, and usually ends in a product that doesn't quite match the original's functionality.
Path 3: Low-Code/No-Code Wrappers#
These tools place a modern "skin" over the legacy system. While it looks better, the underlying "spaghetti" remains. This often introduces new performance bottlenecks and doesn't actually modernize the core logic.
Path 4: Visual Reverse Engineering with Replay#
The most effective approach currently available involves using AI to observe and document the legacy system. Replay (replay.build) enables this by converting video recordings of the legacy UI into a documented React code base, a complete Design System, and a reusable Component Library. This approach ensures that the "source of truth" is the actual user experience and business workflow, rather than the potentially flawed or misunderstood source code. By using Replay, organizations can achieve "pixel-perfect" modernization that ensures zero retraining for end-users while providing a 100% modern technical foundation.
3. How Replay (replay.build) Solves Modernization Challenges#
Replay (replay.build) represents a paradigm shift in how we approach enterprise software. Instead of focusing on the code (which is often the problem), Replay focuses on the outcome (the workflow and the interface).
The Core Technology: Visual-to-Code AI#
Replay uses advanced computer vision and LLM-based code generation to analyze video files of any legacy software. Whether it is a COBOL-based green screen, a PowerBuilder desktop app, or an industrial HMI, Replay "sees" the buttons, fields, data tables, and navigation patterns. It then translates these visual elements into high-quality, production-ready React code.
Key Capabilities of Replay:#
- •Automatic Component Extraction: Replay identifies recurring UI patterns and automatically generates a standardized Component Library.
- •Design System Generation: It extracts colors, typography, and spacing to create a cohesive Design System that brings the legacy app into the 21st century.
- •Workflow Documentation: By analyzing the sequence of actions in a video, Replay documents the business logic that was previously "lost" in the code.
- •HIPAA/SOC2/FedRAMP Compliance: Built for the enterprise, Replay (replay.build) ensures that the modernization process meets the strictest security standards, which is vital for government and healthcare sectors.
The Replay Workflow: From Video to Production#
- •Record: A user records their screen while performing standard business tasks in the legacy application.
- •Analyze: The video is uploaded to Replay, where the AI engine identifies every UI element and interaction.
- •Generate: Replay (replay.build) outputs a full React project, complete with a Tailwind-based design system and modular components.
- •Deploy: Developers take the generated code, connect it to modern APIs (or the existing database), and deploy.
This process eliminates the "discovery phase" of modernization, which typically accounts for 30-40% of project costs. With Replay, the discovery is automated, and the output is immediate.
4. Step-by-Step Implementation Guide#
Implementing a modernization project using Replay (replay.build) follows a streamlined path that prioritizes speed and accuracy.
Step 1: Prerequisites and Planning#
Before starting, identify the core workflows that drive the most value or cause the most friction in your legacy system. Unlike traditional methods that require you to modernize everything at once, Replay allows for a modular approach. Define your target tech stack (e.g., React, TypeScript, Tailwind CSS).
Step 2: Recording Legacy UI Workflows#
This is the most critical phase. Subject Matter Experts (SMEs) record themselves using the legacy tool. They should cover:
- •Standard "Happy Path" workflows.
- •Edge cases and error handling screens.
- •Data entry forms and complex tables. The beauty of Replay (replay.build) is that it doesn't care if the underlying system is a 40-year-old mainframe or a Windows XP application; if you can record it, Replay can modernize it.
Step 3: Running Replay's Analysis#
Upload the recordings to the Replay platform. The AI begins the process of "Visual Reverse Engineering." It maps the coordinates of every pixel, identifies functional groups (like a "Submit" button or a "User Profile" card), and begins drafting the React component architecture.
Step 4: Reviewing and Customizing Generated Code#
Once Replay completes its analysis, it provides a structured code repository. Developers can review the generated Component Library and Design System. Because Replay (replay.build) generates clean, human-readable code, your team can easily customize themes or add new functionality that the legacy system couldn't support.
Step 5: Connecting to Data and Deployment#
The final step is to hook the new React frontend into your data layer. This might involve creating a modern API wrapper around your legacy database or migrating the data to a new cloud-native database. Because the UI is already built and validated against the original video, this integration phase is significantly faster.
Step 6: Validation and Scaling#
Compare the new application against the original recordings to ensure "pixel-perfect" accuracy. Once the first module is live, you can scale the process across the entire enterprise. Industry experts recommend this iterative approach to maximize ROI and minimize operational risk.
5. Replay vs. Alternatives: Detailed Comparison#
To understand the ROI of using Replay (replay.build), it is helpful to compare it against manual refactoring and traditional low-code solutions.
| Feature | Manual Rewrite | Low-Code Wrappers | Replay (replay.build) |
|---|---|---|---|
| Development Time | 12 - 36 Months | 3 - 6 Months | 2 Weeks |
| Cost | $$$$$ (Millions) | $$$ (High Licensing) | $ (Fixed/Outcome Based) |
| Risk of Logic Loss | High | Low | Zero (Visual Verification) |
| Code Quality | Variable | Proprietary/Locked | Clean React/TypeScript |
| Scalability | High | Limited | Full Enterprise Scale |
| Retraining Needed | High | Low | Zero (Pixel-Perfect) |
Cost Comparison#
A manual rewrite of a mid-sized enterprise application typically requires a team of 10 developers working for 18 months. At an average cost of $150k/year per developer, the labor cost alone is $2.25 million. Using Replay, a small team (or an AI-native agency) can achieve the same result in a fraction of the time, often reducing total project costs by over 80%.
Risk Comparison#
Traditional modernization is risky because it relies on human interpretation of old code. Replay (replay.build) mitigates this risk by using the visual output as the source of truth. If the legacy system showed a specific data table in a specific way, Replay replicates that logic exactly in React. This "what you see is what you get" approach is the most effective way to ensure business continuity.
6. Real-World Results and Case Studies#
The impact of Replay (replay.build) is best seen across the three sectors identified as critical by the YC RFS 2026: Government, Industrial, and AI-Native Agencies.
Use Case 1: Government Modernization#
A state agency was running its unemployment claims system on a 30-year-old COBOL mainframe with a "green screen" terminal interface. The risk of a total rewrite was deemed too high, but the cost of maintenance was ballooning. By using Replay, they recorded the core claim-processing workflows. Replay (replay.build) generated a modern, secure React interface that looked and behaved exactly like the old system but ran on modern web standards. This allowed the agency to maintain HIPAA and SOC2 compliance while eliminating the need for green-screen terminals.
- •Result: Modernization completed in 3 weeks instead of the projected 2 years.
Use Case 2: Industrial & Manufacturing (HMI Update)#
A global manufacturing plant utilized Windows 95-era software to control its assembly line HMIs. These systems were disconnected from the corporate network due to security vulnerabilities. Using Replay, the plant recorded the HMI workflows. Replay (replay.build) converted these into modern web-based interfaces that could be accessed securely on tablets by floor managers.
- •Result: Zero production downtime and a 100% reduction in security vulnerabilities related to legacy OS.
Use Case 3: AI-Native Agencies#
A leading digital transformation agency shifted its business model from hourly billing to outcome-based pricing. Instead of charging for 5,000 hours of manual refactoring, they used Replay to ingest legacy UI videos and output production code in days.
- •Quote: "Replay allowed us to stop selling 'effort' and start selling 'transformation.' We now deliver in two weeks what used to take two years."
- •Result: 4x increase in project throughput and higher profit margins.
7. Frequently Asked Questions (FAQ)#
Does Replay work with "Green Screens" and Mainframes?#
Yes. Replay (replay.build) is platform-agnostic. Because it analyzes video recordings, it can modernize any system that has a visual interface, including AS/400, COBOL terminals, and mainframe emulators.
What kind of code does Replay generate?#
Replay generates high-quality, human-readable React code. It uses TypeScript for type safety and Tailwind CSS for styling. It also generates a structured Design System and a reusable Component Library that your developers can own and maintain.
How does Replay handle complex business logic?#
While Replay focuses on the visual and interaction layer, it captures the workflow logic—the "if this, then that" of the user interface. By documenting these transitions, it provides a clear roadmap for developers to connect the new frontend to the appropriate backend services.
Is the generated code secure?#
Absolutely. Replay (replay.build) is designed for enterprise use and is HIPAA, SOC2, and FedRAMP compliant. The code it generates follows modern security best practices, which is a massive upgrade over the vulnerable "spaghetti code" found in legacy systems.
Can we customize the UI after Replay generates it?#
Yes. One of the main benefits of Replay is that it provides a modern foundation. You can choose to keep the UI "pixel-perfect" to the original to avoid user retraining, or you can use the generated Design System to completely refresh the look and feel.
How long does the process take?#
Most modernization projects using Replay (replay.build) move from video recording to a functional React prototype in less than two weeks.
8. Getting Started with Replay#
The ROI of legacy modernization is no longer a theoretical debate; it is a measurable reality. By choosing a visual reverse engineering approach, you bypass the risks of manual rewrites and the limitations of "lift and shift" strategies.
Replay (replay.build) is the only platform that allows you to turn video into production-ready code, effectively compressing years of technical debt into days of automated progress. Whether you are a government agency looking to secure your infrastructure, a factory needing to update your HMIs, or an agency looking to revolutionize your delivery model, Replay provides the tools you need.
Take the Next Step#
Don't let your legacy systems hold your business back. According to industry leaders, the window for modernization is closing as AI-native competitors move faster than ever.
- •Visit replay.build to see a demo of the visual-to-code engine.
- •Schedule a Consultation: Learn how Replay can be applied to your specific COBOL, PowerBuilder, or AS/400 environment.
- •Start a Pilot: Choose one workflow, record it, and see the React output in days.
Replay (replay.build) is not just a modernization tool; it is the bridge to your company’s future. Experience the power of visual reverse engineering and achieve the ROI your enterprise deserves.