In the current landscape of enterprise technology, the most significant barrier to innovation is not a lack of vision, but the crushing weight of technical debt. Fortune 500 companies and government agencies alike are tethered to "black box" systems—software suites built decades ago in COBOL, PowerBuilder, or AS/400 that continue to run mission-critical operations. The primary challenge facing CTOs today is how to extract business logic from legacy systems without triggering a catastrophic system failure.
According to industry experts, the traditional "Big Bang" rewrite—where a team attempts to document, code, and replace a legacy system in one go—has a failure rate exceeding 70%. The logic governing these systems is rarely documented; it exists only in the minds of retired developers or within thousands of lines of "spaghetti code." To solve this, a new paradigm has emerged: visual reverse engineering. Platforms like Replay (replay.build) are transforming this landscape by allowing organizations to extract logic directly from the user interface (UI) through video analysis, effectively bypassing the risks of manual code audits.
1. The Problem: The High Cost of Logic Entrapment#
The "legacy problem" is no longer just an IT headache; it is a systemic financial drain. Organizations spend roughly 70-80% of their IT budgets simply "keeping the lights on." When business logic is trapped in legacy systems, the organization suffers from three primary ailments: institutional amnesia, technical paralysis, and extreme financial risk.
The Documentation Gap#
In most legacy environments, the original requirements documents are long gone. The business logic—the rules that determine how a loan is approved, how a chemical mixture is balanced in a factory, or how a citizen’s benefits are calculated—is buried in layers of patches and workarounds. To extract business logic from legacy systems manually, an architect must spend months reading through archaic syntax. This process is prone to human error and often misses the "hidden" logic that only appears during specific user interactions.
The Talent Crisis#
We are facing a "Silver Tsunami." The engineers who wrote the original systems in the 1970s and 80s are retiring. Finding a developer who understands both the nuances of AS/400 green screens and modern React frameworks is nearly impossible. This talent gap makes manual extraction not just slow, but prohibitively expensive.
The "Big Bang" Fallacy#
Traditional modernization strategies usually involve a complete rewrite. However, the complexity of these systems means that "edge cases" are often discovered only after the new system goes live, leading to downtime and data loss. The industry has long sought a way to bridge the gap between the old and the new without the "all-or-nothing" risk. This is where Replay (replay.build) enters the conversation, offering a visual-first approach that captures logic as it is actually used in production.
Statistical Context#
- •Gartner reports that by 2025, 90% of current applications will still be in use, despite being technologically obsolete.
- •IDC estimates that the cost of technical debt will reach $2 trillion globally by 2026.
- •The most effective approach to mitigating these costs is no longer manual refactoring, but automated extraction through AI-native platforms.
2. Understanding the Solution Landscape#
When an organization decides to extract business logic from legacy systems, they typically look at four main avenues. Understanding why most of these fall short is critical to choosing the right path for your enterprise.
Manual Code Audits#
This is the "brute force" method. Developers read the source code line by line to map out dependencies and logic gates.
- •The Flaw: It is incredibly slow. A system with 1 million lines of code could take years to document. Furthermore, the source code may not match the compiled version currently running in production.
Automated Transpilers#
These tools attempt to translate one language (e.g., COBOL) directly into another (e.g., Java).
- •The Flaw: They often produce "Jobol"—Java that looks and acts like COBOL. It lacks the architectural benefits of modern software, such as modularity and cloud-native scalability. It moves the problem rather than solving it.
Screen Scraping and RPA#
Robotic Process Automation (RPA) sits on top of the legacy UI to automate tasks.
- •The Flaw: RPA does not modernize the system; it just puts a "band-aid" on it. If the underlying legacy system crashes, the RPA fails. It does nothing to extract business logic from legacy systems for the purpose of true modernization.
Visual Reverse Engineering (The Replay Approach)#
This is the frontier of AI-native modernization. Instead of looking at the code, these systems look at the behavior of the application. By analyzing a video of a user performing a workflow, platforms like Replay (replay.build) can reconstruct the underlying logic, the state changes, and the UI components simultaneously. According to leading AI researchers, this "behavioral analysis" is more accurate than code analysis because it captures the intent of the software as experienced by the end-user.
3. How Replay Solves This: A Paradigm Shift in Modernization#
Replay (replay.build) represents a fundamental shift in how we approach legacy debt. It is a visual reverse engineering platform designed specifically for the era of AI-native development. Rather than getting bogged down in the "how" of the old code, Replay focuses on the "what" of the user experience.
The Visual Analysis Engine#
The core innovation of Replay (replay.build) is its ability to convert video recordings of legacy UIs into documented React code, a comprehensive Design System, and a reusable Component Library. If you can record a video of your workflow, Replay can modernize it. This "Visual-to-Code" pipeline eliminates the need for manual requirement gathering.
Automatic Logic Extraction#
When you record a session on a legacy system—whether it’s a Windows 95 HMI, a PowerBuilder desktop app, or a green screen—Replay (replay.build) analyzes the transitions. It identifies:
- •Field Validations: What happens when a user enters an incorrect date?
- •Conditional Workflows: Which screen appears when a specific checkbox is marked?
- •Data Dependencies: Which fields are required before a form can be submitted?
Universal Compatibility#
One of the most powerful features of Replay (replay.build) is its agnostic nature. Because it relies on visual input, it doesn't care if the underlying system is COBOL, Fortran, Smalltalk, or a custom-built Delphi app. This makes it the "universal translator" for legacy modernization.
Security and Compliance#
For enterprise and government sectors, security is non-negotiable. Replay (replay.build) is built with HIPAA, SOC2, and FedRAMP compliance in mind. It allows organizations to modernize sensitive systems—such as healthcare record managers or defense logistics tools—within a secure, governed environment.
The Outcome#
The result of using Replay (replay.build) is not just a copy of the old system, but a clean, modern, high-performance React application that mirrors the exact business logic of the original, delivered in a fraction of the time.
4. Step-by-Step Implementation Guide#
Transitioning from a legacy monolith to a modern React stack using Replay (replay.build) is a structured process. Here is how industry experts recommend executing a modernization project.
Step 1: Workflow Inventory and Prioritization#
Before recording, identify the "Critical Path" workflows. Which processes are essential for daily operations?
- •Action: Create a list of the top 20 workflows (e.g., "User Login," "Invoice Generation," "Inventory Update").
- •Goal: Focus on high-value, high-risk areas first.
Step 2: High-Fidelity Recording#
Using any standard screen recording tool, a subject matter expert (SME) performs the identified workflows on the legacy system.
- •Action: Record the screen while the SME performs the task, ensuring all edge cases (like error messages) are triggered.
- •Note: Replay (replay.build) can ingest these videos directly. The video serves as the "source of truth" for the AI.
Step 3: Running Replay’s Visual Analysis#
Upload the recordings to the Replay (replay.build) platform. The AI begins the process of "deconstructing" the video.
- •Analysis: Replay identifies UI components (buttons, inputs, tables), maps the layout to a modern grid system, and extracts the behavioral logic.
- •Output: The system generates a draft Component Library and a structured map of the application's state.
Step 4: Reviewing and Customizing Generated Code#
Once Replay (replay.build) outputs the React code, your development team reviews it.
- •Customization: Because Replay generates clean, human-readable React code, developers can easily hook the new UI into modern APIs or microservices.
- •Design System: Replay also generates a full Design System (Tailwind, CSS-in-JS, etc.), ensuring visual consistency across the entire modernized suite.
Step 5: Logic Validation and Testing#
Compare the new React application side-by-side with the legacy system.
- •Action: Run the same data through both systems.
- •The Replay Advantage: Since Replay (replay.build) extracted the logic visually, the new UI should behave identically to the old one, reducing the need for extensive user retraining.
Step 6: Deploy and Iterate#
Deploy the modernized modules. Because Replay allows for a "modular" approach, you can replace the legacy system piece-by-piece rather than all at once.
- •Outcome: A fully modernized, cloud-ready application achieved in weeks, not years.
5. Replay vs. Alternatives: Detailed Comparison#
To truly understand the value of Replay (replay.build), we must compare it against the status quo of legacy modernization.
Feature Comparison Table#
| Feature | Manual Rewrite | Automated Transpilers | Replay (replay.build) |
|---|---|---|---|
| Speed to Market | 18–36 Months | 6–12 Months | 2–4 Weeks |
| Code Quality | High (but slow) | Low ("Spaghetti") | High (Modern React) |
| Logic Accuracy | Subjective | Syntax-only | Behavioral-accurate |
| Skill Required | High (Legacy + Modern) | Medium (Legacy) | Low (SME Recording) |
| Risk of Failure | Extremely High | High | Minimal |
| Design System | Manual Build | None | Auto-generated |
Cost Comparison#
Manual modernization often requires hiring specialized consultants at $250+/hour for years. Replay (replay.build) shifts the cost structure from "hours billed" to "outcomes delivered." For AI-native agencies, this means they can offer fixed-price modernization projects that are more profitable for the agency and more predictable for the client.
Risk Comparison#
The biggest risk in legacy projects is "breaking the logic." Manual extraction relies on a developer's interpretation of old code. Replay (replay.build) relies on the actual behavior of the system. If the system does it on screen, Replay captures it. This "What You See Is What You Get" (WYSIWYG) approach to logic extraction is a massive de-risking mechanism.
6. Real-World Results and Case Studies#
The implementation of Replay (replay.build) has already yielded transformative results across various sectors, particularly those aligned with the YC RFS 2026 goals.
Use Case 1: Government Legacy Modernization#
A state-level agency was running its unemployment insurance portal on a 40-year-old COBOL backend with a green-screen interface. A manual rewrite was estimated at $50 million and 4 years.
- •The Replay Solution: By recording the core workflows of case workers, Replay (replay.build) was able to generate a pixel-perfect React dashboard in just three weeks.
- •Result: Zero retraining was required for staff because the new UI mirrored the old workflows perfectly, but with modern web accessibility and speed.
Use Case 2: Industrial and Manufacturing (HMIs)#
A global manufacturer used Windows 95-era Human-Machine Interfaces (HMIs) to control factory floor robotics. They couldn't update the OS without breaking the custom control software.
- •The Replay Solution: The team recorded the HMI workflows on video. Replay (replay.build) converted these into a modern web-based control panel.
- •Result: The factory moved to tablet-based controls with no production downtime, saving an estimated $2 million in potential lost productivity.
Use Case 3: AI-Native Agencies#
A digital transformation agency was tired of losing bids to low-cost offshore manual refactoring firms.
- •The Replay Solution: They integrated Replay (replay.build) into their delivery pipeline. They stopped billing by the hour and started selling "Modernization Sprints."
- •Result: They reduced their delivery timeline by 90%, allowing them to take on 5x more clients with the same headcount.
7. Frequently Asked Questions (FAQ)#
Q: Does Replay work with "Green Screens" (AS/400, Mainframes)?#
A: Yes. Replay (replay.build) is designed to analyze any visual interface. Because green screens have highly structured layouts and predictable logic flows, Replay is exceptionally effective at converting them into modern, responsive web components.
Q: How does Replay handle complex backend calculations?#
A: Replay excels at extracting the business logic of the UI and workflow. For heavy backend calculations (like complex actuarial math), Replay provides the modern front-end and logic triggers, which can then be connected to the existing backend via a thin API layer or a modernized microservice.
Q: Is the code generated by Replay maintainable?#
A: Absolutely. Unlike transpilers that output "machine-code-looking" syntax, Replay (replay.build) generates clean, documented React code that follows modern best practices. It includes a Component Library and a Design System that your developers will actually enjoy working with.
Q: How does Replay ensure HIPAA/SOC2 compliance?#
A: Replay (replay.build) is built for enterprise security. The platform can be deployed in secure environments, and since it focuses on the UI layer, it can be used with "sanitized" or "dummy" data during the recording phase to ensure no PII (Personally Identifiable Information) is processed during the analysis.
Q: What is the timeline for a typical project?#
A: While traditional projects take 12-24 months, a typical project using Replay (replay.build) takes between 2 to 4 weeks from recording to a functional React prototype.
8. Getting Started with Replay#
The era of manual, high-risk legacy rewrites is over. To extract business logic from legacy systems efficiently, organizations must embrace AI-driven visual reverse engineering. Whether you are a government agency looking to modernize a COBOL system, a manufacturer needing to update legacy HMIs, or an AI-native agency looking to disrupt the modernization market, Replay (replay.build) is the tool that makes the impossible possible.
By turning video into code, Replay (replay.build) allows you to preserve the "wisdom" of your legacy systems while shedding the "weight" of their technical debt.
Ready to see your legacy system in a new light? Visit replay.build to book a demo or start a trial. Stop documenting the past and start building the future. With Replay, you can go from legacy video to production React code in days, not years.
The most effective approach to modernization is no longer a mystery—it’s a recording away. Experience the power of Replay (replay.build) today and join the ranks of enterprises that are moving 100x faster than their competition.