AS/400 Inventory Screens to Mobile-Ready React: How to Slash Development Time by 75%

The IBM i (AS/400) is the "cockroach" of the enterprise architecture—indestructible, ubiquitous, and increasingly difficult to interface with in a mobile-first world. While these systems power the backbones of global logistics, manufacturing, and financial services, they are often trapped behind 5250 "green screens" that require specialized knowledge and tethered workstations. The push to make as400 inventory screens mobileready is no longer a luxury; it is a survival requirement for organizations facing a $3.6 trillion global technical debt.

Traditional modernization efforts are notorious for their failure rates. Industry data shows that 70% of legacy rewrites fail or significantly exceed their timelines. When you consider that the average enterprise rewrite takes 18 months, the risk profile of moving inventory logic from a terminal to a modern React application is staggering. Most of this time isn't spent coding; it's spent in the "discovery phase," trying to document business logic that was written in RPG or COBOL forty years ago by developers who have since retired.

TL;DR: Modernizing AS/400 inventory systems manually takes roughly 40 hours per screen and carries a 70% failure risk. By using Replay and its Visual Reverse Engineering engine, enterprises can reduce that time to 4 hours per screen—a 75-90% reduction in development effort. This guide explores how to transform legacy terminal workflows into documented, mobile-ready React component libraries without the 18-month roadmap.

---

The Documentation Gap: Why Manual Rewrites Stumble#

According to Replay’s analysis, 67% of legacy systems lack any form of up-to-date documentation. In the context of inventory management, this is catastrophic. An inventory screen isn't just a list of parts; it represents complex state transitions, validation logic for SKU formats, and intricate warehouse bin-location rules.

When an architect attempts to make as400 inventory screens mobileready, they usually start by interviewing users and "screen scraping." This manual process is error-prone. Developers spend weeks trying to replicate the exact behavior of a legacy system they don't fully understand.

Visual Reverse Engineering is the process of capturing real-time user interactions with legacy systems and automatically generating the underlying architectural maps, design tokens, and functional code required for a modern replacement.

By recording a user performing a standard inventory cycle count on an AS/400 terminal, Replay identifies the data entry patterns, the navigational flows, and the UI constraints. Instead of a developer spending 40 hours manually recreating a "Part Inquiry" screen, Replay’s AI Automation Suite extracts the essence of that screen into a documented React component in a fraction of the time.

Learn more about modernizing legacy UI

---

Transforming AS400 Inventory Screens Mobileready: The Technical Hurdle#

The primary challenge in making as400 inventory screens mobileready is the shift from a fixed-grid terminal (usually 24x80 or 27x132 characters) to a fluid, responsive layout. A warehouse worker on a zebra scanner or an iPad needs a touch-optimized interface, not a keyboard-driven one.

The Componentization Strategy#

To move fast, you cannot simply "re-skin" the terminal. You must extract the components. In the AS/400 world, a screen might contain:

1. •Header metadata (Warehouse ID, Date, User)
2. •Search filters (Part Number, Category)
3. •A subfile (the list of inventory items)
4. •Function key legends (F3=Exit, F5=Refresh)

Industry experts recommend moving toward an Atomic Design pattern during this transition. This is where Replay’s "Library" feature becomes essential. It identifies repeating patterns across hundreds of inventory screens and consolidates them into a single, governed Design System.

Comparison: Manual Modernization vs. Replay VRE#

---

Implementing the React Inventory Layer#

Once Replay has processed the recording of your AS/400 workflow, it generates "Blueprints"—high-fidelity, editable representations of your legacy UI. From here, you can export clean, production-ready TypeScript code.

Below is an example of what a modernized inventory list component looks like once it has been extracted and converted into a mobile-ready React structure.

typescript
// Generated via Replay AI Automation Suite
import React, { useState } from 'react';
import { Card, Badge, Button, Input } from '@/components/ui';
import { Search, Package, MapPin } from 'lucide-react';

interface InventoryItem {
  id: string;
  sku: string;
  description: string;
  quantity: number;
  location: string;
  status: 'In Stock' | 'Low Stock' | 'Out of Stock';
}

export const InventoryMobileList: React.FC<{ items: InventoryItem[] }> = ({ items }) => {
  const [searchTerm, setSearchTerm] = useState('');

  const filteredItems = items.filter(item => 
    item.sku.toLowerCase().includes(searchTerm.toLowerCase()) ||
    item.description.toLowerCase().includes(searchTerm.toLowerCase())
  );

  return (
    <div className="flex flex-col space-y-4 p-4 bg-slate-50 min-h-screen">
      <div className="relative">
        <Search className="absolute left-3 top-3 h-4 w-4 text-slate-400" />
        <Input 
          placeholder="Search SKU or Description..." 
          className="pl-10"
          value={searchTerm}
          onChange={(e) => setSearchTerm(e.target.value)}
        />
      </div>

      {filteredItems.map((item) => (
        <Card key={item.id} className="p-4 shadow-sm border-l-4 border-l-blue-500">
          <div className="flex justify-between items-start">
            <div>
              <h3 className="font-bold text-lg text-slate-900">{item.sku}</h3>
              <p className="text-sm text-slate-500">{item.description}</p>
            </div>
            <Badge variant={item.status === 'In Stock' ? 'success' : 'warning'}>
              {item.status}
            </Badge>
          </div>
          
          <div className="mt-4 flex items-center justify-between text-sm">
            <div className="flex items-center text-slate-600">
              <Package className="mr-2 h-4 w-4" />
              <span>Qty: <strong>{item.quantity}</strong></span>
            </div>
            <div className="flex items-center text-slate-600">
              <MapPin className="mr-2 h-4 w-4" />
              <span>{item.location}</span>
            </div>
          </div>
          
          <Button className="w-full mt-4" variant="outline">
            Update Stock
          </Button>
        </Card>
      ))}
    </div>
  );
};

This code represents a radical departure from the 5250 terminal. It utilizes modern hooks, responsive utility classes (Tailwind), and accessible components. Crucially, Replay ensures that the data mapping—the "SKU" field on the React side—perfectly matches the field lengths and validation rules found in the original IBM i physical files.

---

Bridging the Gap with Flows and Blueprints#

One of the most significant risks in making as400 inventory screens mobileready is breaking the "hidden" navigation logic. In an AS/400 environment, navigation is often handled by specific command keys (F-keys) or hidden numeric options (e.g., typing '5' next to a line item to view details).

Replay Flows solves this by mapping the user journey visually. When you record a workflow, Replay doesn't just see the screens; it sees the relationship between them. It builds a state machine that describes how a user moves from "Warehouse Selection" to "Aisle Selection" to "Bin Count."

This architectural map is vital for developers. Instead of guessing how the legacy application handles errors or multi-page subfiles, they can reference the Flow map. This visibility is why Replay users see an average of 70% time savings. You aren't just writing code; you are implementing a verified architectural blueprint.

Read about automated architectural mapping

---

Security and Compliance in Regulated Environments#

For industries like Healthcare and Financial Services, the AS/400 is often the system of record because of its legendary security and auditability. Moving this data to a mobile React frontend introduces new security vectors.

Replay is built for these high-stakes environments. The platform is SOC2 compliant and HIPAA-ready. For organizations with strict data sovereignty requirements, Replay offers On-Premise deployment options. This ensures that the process of making as400 inventory screens mobileready doesn't compromise the integrity of the underlying IBM i data or expose sensitive PII (Personally Identifiable Information) during the reverse engineering process.

Replay allows teams to:

• •Sanitize recordings to remove sensitive data before processing.
• •Generate code that adheres to modern security standards (OWASP).
• •Maintain a clear audit trail of how legacy logic was translated into modern components.

---

The "Mobile-Ready" Logic: Handling Connectivity#

Inventory management often happens in "dead zones"—areas of a warehouse with poor Wi-Fi. A terminal-based system fails immediately if the connection drops. A modern React application can do better.

When Replay generates your components, it provides the foundation for implementing Progressive Web App (PWA) features. By leveraging service workers and IndexedDB, you can allow warehouse staff to continue their inventory counts offline and sync back to the AS/400 via a REST or GraphQL API once connectivity is restored.

Example: Offline-First State Management#

typescript
// Example of a sync-capable hook for AS/400 inventory updates
import { useMutation, useQueryClient } from '@tanstack/react-query';
import { updateAS400Stock } from '@/api/inventory';

export const useUpdateStock = () => {
  const queryClient = useQueryClient();

  return useMutation({
    mutationFn: updateAS400Stock,
    // Optimistic updates for better mobile UX
    onMutate: async (newUpdate) => {
      await queryClient.cancelQueries({ queryKey: ['inventory'] });
      const previousInventory = queryClient.getQueryData(['inventory']);
      
      queryClient.setQueryData(['inventory'], (old: any) => 
        old.map((item: any) => item.id === newUpdate.id ? { ...item, ...newUpdate } : item)
      );

      return { previousInventory };
    },
    onError: (err, newUpdate, context) => {
      queryClient.setQueryData(['inventory'], context?.previousInventory);
    },
    onSettled: () => {
      queryClient.invalidateQueries({ queryKey: ['inventory'] });
    },
  });
};

This level of sophistication is what separates a simple screen-scrape from a true modernization effort. By using Replay to handle the UI and architectural extraction, your senior engineers can focus on these high-value features like offline synchronization and complex state management.

---

Why Speed Matters: The Opportunity Cost of Technical Debt#

Every month your inventory team spends fighting with a green screen is a month of lost productivity. Manual data entry from paper forms back into an AS/400 terminal leads to an average error rate of 2-5%. In a high-volume warehouse, that translates to thousands of dollars in lost stock and shipping errors.

By making as400 inventory screens mobileready in weeks rather than years, you capture immediate ROI:

1. •Reduced Training Time: New hires understand a mobile app in minutes; learning green screen commands takes weeks.
2. •Increased Accuracy: Barcode scanning integration (easily added to React) eliminates manual entry errors.
3. •Real-time Visibility: Management sees stock levels as they happen, not at the end of a shift.

According to Replay's analysis, the cost of delaying modernization is often higher than the cost of the project itself. With an 18-month average enterprise rewrite timeline, many companies find their "modern" solution is already outdated by the time it launches. Replay breaks this cycle by providing a "Fast Track" from recording to React.

---

Summary of the Replay Workflow#

1. •Record: Use the Replay recorder to capture standard inventory workflows on your existing AS/400 screens.
2. •Analyze: Replay’s AI Automation Suite identifies UI patterns, data fields, and navigation flows.
3. •Organize: Centralize components in the Replay Library to build a consistent Design System.
4. •Refine: Use the Blueprint editor to tweak the layout for mobile responsiveness.
5. •Export: Generate clean TypeScript/React code and integrate it with your backend APIs.

This process transforms the daunting task of making as400 inventory screens mobileready into a structured, repeatable engineering exercise.

---

Frequently Asked Questions#

Does Replay require access to my AS/400 source code?#

No. Replay uses Visual Reverse Engineering to analyze the user interface and interactions. It does not need to read your RPG or COBOL source code, which is ideal for systems where the source code has been lost or is poorly documented.

How does Replay handle complex AS/400 subfiles?#

Replay’s AI recognizes common terminal patterns like subfiles (lists). It automatically converts these into modern, paginated, or infinitely scrolling React tables/lists, preserving the data relationships while improving the user experience.

Can I use the generated React code with my existing APIs?#

Yes. Replay generates the frontend UI and the architectural logic. You can easily hook the generated React components into your existing IBM i APIs (REST, SOAP, or even middleware like Mulesoft or Profound UI).

Is the generated code maintainable?#

Absolutely. Unlike "black box" modernization tools, Replay provides you with standard, high-quality TypeScript and React code. There is no proprietary runtime required. Once the code is exported, it is yours to maintain and evolve using standard dev tools.

What is the average time savings for a large-scale project?#

While individual screens see a 75-90% reduction in dev time (from 40 hours to 4 hours), entire projects typically see an overall time saving of 70%. This includes the time needed for API integration and end-to-end testing.

---

Ready to modernize without rewriting? Book a pilot with Replay and see how quickly your legacy inventory screens can become a modern, mobile-ready reality.