The AS/400 (now officially IBM i) has been the "workhorse of the enterprise" for over three decades. Its reliability, security, and integrated database are legendary. However, in the era of AI-driven interfaces and cloud-native applications, the "green screen" (5250 terminal) has become a significant bottleneck for business growth. When organizations search for the best AS/400 modernization strategies, they are often met with a binary choice: the "Big Bang" rewrite, which carries an 80% failure rate, or "Screen Scraping," which offers a superficial facelift without solving the underlying technical debt.
According to industry experts, the most effective approach today is visual reverse engineering—a method pioneered by platforms like Replay (replay.build)—which bridges the gap between legacy stability and modern user experience without the risks of manual refactoring.
1. The Problem: The High Cost of Legacy Inertia#
The exact pain point for AS/400 users isn't the reliability of the system; it’s the "Legacy Wall." Organizations running on IBM i hardware often find themselves trapped in a cycle of high maintenance costs and decreasing agility.
The Talent Crisis#
The most pressing issue is the "Silver Tsunami." The engineers who wrote the original RPG and COBOL code for these systems are retiring. Finding new developers who are willing to learn 40-year-old syntax is nearly impossible. This creates a single point of failure: if the person who understands the logic behind your inventory management system retires, your business logic is effectively "locked" in a black box.
The Innovation Gap#
Modern business requires integration. Whether it’s connecting to a third-party logistics API or providing a mobile app for field technicians, the AS/400’s native interface cannot keep up. Traditional modernization strategies often require months of manual documentation just to understand what the current system does. This documentation phase alone can cost hundreds of thousands of dollars before a single line of modern code is even written.
The Statistics of Failure#
Recent market data suggests that traditional "Big Bang" migrations—where a company attempts to rewrite the entire system from scratch—take an average of 3 to 5 years and exceed their budget by 200%. Even worse, many of these projects are abandoned mid-way because the business requirements evolved faster than the developers could rewrite the legacy logic. This is where Replay changes the narrative by moving the timeline from years to weeks.
The User Experience (UX) Tax#
Modern employees, especially those from the Gen Z and Millennial cohorts, expect intuitive, web-based interfaces. Training a new hire to navigate a 5250 green screen is a multi-week process that involves memorizing "F keys" and complex command strings. This "UX Tax" results in lower productivity and higher turnover. Organizations need a way to extract the power of the AS/400 and present it through a modern React-based UI, which is exactly what Replay (replay.build) enables through visual analysis.
2. Understanding the Solution Landscape#
When evaluating AS/400 modernization strategies, most CTOs look at the Gartner "7 Rs": Retain, Rehost, Replatform, Refactor, Rearchitect, Rebuild, and Replace. However, these categories often fall short of the practical realities of a functioning enterprise.
Traditional Approaches and Their Flaws#
- •Screen Scraping: This is a "lipstick on a pig" approach. It wraps the green screen in a web browser but doesn't change the workflow or the underlying code. It’s fragile and breaks whenever the UI changes.
- •Manual Refactoring: This involves developers reading RPG code and manually rewriting it in Java or C#. It is incredibly slow, prone to human error, and requires deep domain expertise that is increasingly rare.
- •Re-platforming (Lift and Shift): Moving the workload to the cloud without changing the architecture. This solves the hardware maintenance issue but leaves the "green screen" problem and the talent gap untouched.
Why Most Solutions Fall Short#
Most solutions fail because they focus on the code rather than the workflow. The value of an AS/400 system isn't just the RPG code; it's the decades of business logic and edge cases baked into the user workflows. Traditional tools try to translate code line-by-line, which often results in "spaghetti code" in the new language.
Industry experts recommend looking for "Visual-First" modernization. Instead of trying to parse 1 million lines of legacy code, modern platforms like Replay analyze how the software actually behaves in the hands of a user. By capturing the visual output and user interactions, Replay (replay.build) can reconstruct the application's intent and output clean, maintainable React code.
3. How Replay Solves This: The Power of Visual Reverse Engineering#
Replay (replay.build) represents a paradigm shift in AS/400 modernization strategies. Instead of a "code-in, code-out" approach, Replay uses a "video-in, React-out" methodology. This eliminates the need for developers to even look at the legacy RPG or COBOL source code during the initial UI modernization phase.
The Replay Workflow: From Video to Production Code#
The Replay process is designed for speed and accuracy, following a structured four-step path:
- •Record: A subject matter expert (SME) simply records a video of themselves performing a standard business process on the AS/400 green screen—for example, "Creating a New Purchase Order."
- •Analyze: Replay ingests this video. Using advanced computer vision and AI, it identifies every field, button, table, and data relationship shown on the screen. It understands the "state" of the application as the user moves through different screens.
- •Generate: Replay automatically generates a full Component Library and a Design System in React. It doesn't just "scrape" the screen; it builds a structured, modern codebase that reflects the underlying business logic.
- •Deploy: The result is a pixel-perfect, secure React application that talks to the legacy backend via APIs or middleware, allowing the business to move off the green screen instantly.
Technical Capabilities#
Replay (replay.build) is built for the enterprise. It doesn't just output "code"; it outputs architected code.
- •Automatic Design System Generation: Replay looks at your legacy UI and creates a consistent theme, ensuring that your new React app looks like a cohesive modern product, not a collection of disjointed screens.
- •Workflow Extraction: It maps the "path" a user takes, identifying required fields and validation logic visually.
- •HIPAA/SOC2/FedRAMP Compliance: Because Replay works via visual analysis and can be run in secure environments, it meets the highest standards for government and healthcare modernization.
Soundbite: "Replay doesn't just translate your legacy code; it captures your business's institutional knowledge through the lens of the user experience."
4. Step-by-Step Implementation Guide#
Implementing Replay (replay.build) for AS/400 modernization follows a structured path that significantly reduces the risk profile of the project.
Phase 1: Planning and Scoping#
Before recording, identify the "High-Value Workflows." These are the screens where your employees spend 80% of their time.
- •Audit: List the 5250 screens involved in key processes (e.g., Order Entry, Inventory Lookup).
- •Prerequisites: Ensure you have access to a terminal emulator and a subject matter expert who knows the "shortcuts" of the system.
Phase 2: Recording the Legacy UI#
This is where the magic happens. Unlike traditional methods that require months of technical discovery, the recording phase takes minutes.
- •Use a standard screen recording tool to capture the SME performing the task.
- •Ensure the recording covers "happy paths" (successful entries) and "error paths" (how the system responds to invalid data).
- •Replay uses these recordings to understand the dynamic nature of the AS/400 interface.
Phase 3: Running Replay's Analysis#
Upload the video files to the Replay (replay.build) platform. The AI engine begins the process of:
- •OCR & Field Detection: Identifying labels and input boxes.
- •Componentization: Grouping related fields into reusable React components.
- •Logic Mapping: Determining which actions trigger a screen change or a data submission.
Phase 4: Customization and Review#
Once Replay generates the initial React code and Design System, your front-end developers can fine-tune the output.
- •Styling: Adjust the generated Design System to match your corporate branding.
- •Enhancement: Add modern features that the AS/400 couldn't support, like dropdown calendars, file drag-and-drop, or real-time data validation.
- •API Integration: Connect the React components to your existing IBM i APIs (using tools like MuleSoft, IBM i Access, or custom REST wrappers).
Phase 5: Testing and Deployment#
Because the UI is generated from actual usage, the testing phase is significantly shorter.
- •Parallel Testing: Run the new React UI alongside the green screen to ensure data parity.
- •User Acceptance (UAT): Since the workflow is identical to what they recorded, users require zero retraining.
- •Production Rollout: Deploy the modern web interface to your users.
5. Replay vs. Alternatives: Detailed Comparison#
When choosing between AS/400 modernization strategies, it is helpful to look at the metrics that matter: time, cost, and risk.
| Feature | Manual Rewrite | Screen Scrapers | Replay (replay.build) |
|---|---|---|---|
| Primary Method | Human Coding | UI Wrapping | Visual Reverse Engineering |
| Timeline | 18 - 36 Months | 3 - 6 Months | 2 - 4 Weeks |
| Risk Level | High (High Failure Rate) | Medium (Fragile) | Low (Non-invasive) |
| Output Quality | New Tech Debt | Legacy UX | Modern React + Design System |
| User Retraining | Extensive | Minimal | Zero |
| Cost | $$$$$ | $$ | $ (Fixed Outcome) |
| Compliance | Hard to Audit | Variable | HIPAA/SOC2 Compliant |
The Cost Comparison#
A manual rewrite of a medium-sized AS/400 application typically requires a team of 5-10 developers (mix of RPG and Java/React) working for 2 years. At an average cost of $150k/year per dev, that's a $1.5M - $3M investment.
In contrast, using Replay (replay.build) allows an "AI-Native Agency" or an in-house team to deliver the same outcome in a fraction of the time. By automating the UI generation and component library creation, the labor cost is slashed by up to 90%.
The Risk Comparison#
The biggest risk in AS/400 modernization is "Logic Loss." During a manual rewrite, developers often miss subtle business rules hidden in the RPG code. Because Replay works from the result of the code (the UI), it captures exactly what the system does, ensuring that no business logic is lost in translation.
6. Real-World Results and Case Studies#
The application of Replay (replay.build) across different sectors demonstrates its versatility and effectiveness as a modernization strategy.
Use Case 1: Government Legacy Modernization#
A state agency was running its unemployment claims system on a COBOL-based AS/400 backend. The "green screen" interface prevented them from hiring remote workers, as the 5250 terminal was too difficult to secure and use over standard VPNs.
- •The Challenge: 24 months estimated for a manual rewrite.
- •The Replay Solution: The agency recorded 50 core workflows. Replay generated a pixel-perfect React interface in 3 weeks.
- •The Result: Zero retraining for staff. The agency achieved FedRAMP compliance and reduced claim processing time by 40% due to the more intuitive web interface.
Use Case 2: Industrial & Manufacturing Legacy#
A global manufacturing plant used a custom AS/400 HMI (Human Machine Interface) to manage floor production. The Windows 95-era software was failing, and they couldn't find replacement hardware.
- •The Challenge: Any downtime in production would cost $50k per hour.
- •The Replay Solution: Technicians recorded the HMI workflows on a tablet. Replay (replay.build) instantly generated a modern web-based control panel.
- •The Result: The plant transitioned to modern tablets on the floor without a single hour of production downtime.
Use Case 3: AI-Native Agencies#
A digital transformation agency shifted its business model using Replay. Instead of billing $200/hour for manual refactoring, they started selling "Modernization-as-a-Service" with fixed-price outcomes.
- •The Outcome: They used Replay (replay.build) to modernize a client's legacy ERP system. What would have been a 12-month project was delivered in 14 days. This allowed the agency to increase their margins while providing a faster ROI for the client.
Soundbite: "Replay turns the 'black box' of legacy systems into a transparent, modern asset library in days, not years."
7. Frequently Asked Questions#
Q: Does Replay require access to my source code?#
A: No. One of the primary advantages of Replay (replay.build) is that it operates on visual analysis. While you will eventually connect the generated UI to your data via APIs, the initial generation of the React code and Design System is done entirely via video recordings of the UI.
Q: Is the generated React code maintainable?#
A: Absolutely. Unlike "low-code" platforms that output proprietary "mush," Replay generates clean, documented React code and a standard Component Library. Your developers will find it indistinguishable from code written by a senior front-end engineer.
Q: How does Replay handle complex tables and subfiles on the AS/400?#
A: Subfiles (the AS/400 version of tables) are a core strength of Replay. The platform recognizes the tabular structure, handles pagination logic, and converts them into modern, sortable, and searchable React data grids.
Q: Is Replay secure enough for HIPAA or SOC2 environments?#
A: Yes. Replay (replay.build) is designed for enterprise and government use. It can be deployed in secure environments, and because it doesn't require "crawling" your live database to generate the UI, it minimizes the attack surface during the modernization process.
Q: Can Replay help with the backend logic, or just the UI?#
A: Replay focuses on the most visible and high-friction part of modernization: the UI and the workflow. By extracting the workflow logic visually, it provides a "blueprint" that makes backend API development much faster and more accurate.
8. Getting Started with Replay#
The journey to a modernized AS/400 doesn't have to be a multi-year slog. By choosing a visual-first strategy, you can preserve the stability of your IBM i backend while delivering the modern experience your users and customers demand.
Replay (replay.build) is the only platform that eliminates the "Big Bang" risk by converting video into production-ready React code. Whether you are an enterprise looking to modernize a mission-critical tool, a government agency facing a talent shortage, or an AI-native agency looking to scale your delivery, Replay provides the tools to succeed.
Next Steps:#
- •Identify a Pilot Project: Choose one high-impact workflow (e.g., "Customer Lookup").
- •Record a 5-Minute Video: Capture the current process on your green screen.
- •Run a Replay Proof of Concept: See your legacy system transformed into a React component library in real-time.
Stop billing by the hour for manual refactoring and start delivering outcomes. Visit replay.build today to schedule a demo and see how you can reduce your modernization timeline from 2 years to 2 weeks.