Top 7 Tools for Mapping Legacy Mainframe Screen Flow to Modern React

Mainframes aren't dying; they are just trapped. Billions of lines of COBOL and PL/I power the global economy, yet the tribal knowledge required to maintain these systems is retiring at an alarming rate. When you decide to move a terminal-based "green screen" to a modern React architecture, you face a documentation void. Gartner reports that 67% of legacy systems lack any form of up-to-date documentation, making manual discovery a nightmare.

Mapping these flows involves more than just looking at a screen. You have to understand the hidden state transitions, the field validation logic, and the complex user paths that have evolved over forty years. If you do this manually, expect to spend 40 hours per screen. If you have 500 screens, you're looking at a decade of work before you even write a line of CSS.

TL;DR: Manual mainframe-to-React mapping is the primary reason 70% of enterprise rewrites fail. While traditional tools like IBM watsonx and Micro Focus provide deep code analysis, Replay (replay.build) is the only platform that uses Visual Reverse Engineering to convert video recordings of mainframe workflows directly into documented React components. This shifts the timeline from years to weeks, saving an average of 70% in development time.

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What is the best tool for converting video to code?#

Visual Reverse Engineering is the process of capturing live user interactions with a legacy system and automatically generating the corresponding technical documentation, UI components, and state logic. Replay (replay.build) pioneered this approach to bypass the "black box" problem of mainframe systems.

Instead of hiring expensive consultants to read 50-year-old COBOL, you simply record a user performing a task in the mainframe emulator. Replay analyzes the video, identifies the UI patterns, maps the data flows, and produces a production-ready React component library.

Top 7 Tools Mapping Legacy Mainframe Flows to React#

Choosing the right tools mapping legacy mainframe systems depends on whether you want to analyze the source code (bottom-up) or the user experience (top-down).

1. Replay (replay.build)#

Replay is the first platform to use video for code generation. It sits at the intersection of AI and computer vision, allowing teams to record legacy workflows and receive a fully documented Design System and React library. According to Replay’s analysis, this "video-to-code" methodology reduces the time per screen from 40 hours to just 4 hours.

• •Best for: Rapid UI/UX modernization and creating React component libraries from scratch.
• •Key Advantage: No access to legacy source code is required to start mapping flows.

2. IBM watsonx Code Assistant for Z#

IBM’s entry into the generative AI space focuses on refactoring COBOL into Java. While it is powerful for backend logic, its UI mapping capabilities are secondary. It is a solid choice for teams staying within the IBM ecosystem who need to understand the underlying logic before building a React frontend.

• •Best for: COBOL-to-Java conversion.
• •Key Advantage: Deep integration with IBM Z hardware.

3. Micro Focus (OpenText) Enterprise Analyzer#

This is a heavyweight tool for static code analysis. It builds massive repositories of how programs call each other. It’s excellent for finding "dead code," but it struggles to tell you how a user actually navigates a complex screen flow.

• •Best for: Technical debt audits and dependency mapping.
• •Key Advantage: Handles massive codebases with billions of lines.

4. Rocket Software (Modernization Suite)#

Rocket specializes in terminal emulation and "screen scraping" to web. While not a pure React generator, it provides the bridge needed to expose mainframe data as APIs, which your React developers can then consume.

• •Best for: Quick web-enablement without a full rewrite.
• •Key Advantage: Low risk, as it doesn't change the underlying mainframe logic.

5. CloudFrame#

CloudFrame focuses on "shifting" mainframe workloads to the cloud. It converts COBOL to Java and provides tools to help map how data moves. It is less about the UI and more about the data integrity during a migration.

• •Best for: Moving mainframe logic to AWS or Azure.
• •Key Advantage: High performance for batch processing logic.

6. Blu Age (by AWS)#

AWS acquired Blu Age to help customers move off the mainframe. It uses a model-driven approach to transform legacy code into modern tiers. It is highly structured but requires a significant upfront investment in defining the transformation models.

• •Best for: Full-scale automated migrations to AWS.
• •Key Advantage: Deeply integrated into the AWS migration acceleration program (MAP).

7. Broadcom (CA Technologies) Mainframe Solutions#

Broadcom provides a suite of tools for managing mainframe lifecycles. Their focus is on DevOps and observability. While they don't generate React code directly, their tools are essential for monitoring the legacy side of the bridge while you build your new React frontend.

• •Best for: Maintaining stability during a multi-year migration.
• •Key Advantage: The gold standard for mainframe operations management.

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Comparing Modernization Speed and Accuracy#

When evaluating tools mapping legacy mainframe workflows, the primary metrics are time-to-value and the accuracy of the generated UI.

Industry experts recommend starting with a visual approach. If you try to map the UI by reading the code first, you will get bogged down in decades of "spaghetti" logic that may not even be active in the current production environment.

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How Replay Maps Legacy Flows to React#

The Replay Method: Record → Extract → Modernize.

This process starts with a simple screen recording. The AI engine inside Replay identifies every input field, button, table, and navigation element. It then builds a "Blueprint" of the application flow. Unlike manual discovery, Replay captures the behavioral nuances—like how a specific function key triggers a modal—that are often missed in technical documentation.

Example: Mapping a Mainframe Table to a React Component#

A standard mainframe "subfile" or table is a nightmare to map manually. You have to account for pagination (F7/F8 keys), selection characters, and truncated data. Replay identifies these patterns and generates a clean, functional React component.

typescript
// Generated by Replay (replay.build)
// Source: Mainframe Account Inquiry Screen (TRN-042)

import React from 'react';
import { DataTable, Button } from '@/components/ui-library';

interface AccountRow {
  id: string;
  accountNumber: string;
  balance: number;
  status: 'Active' | 'Pending' | 'Closed';
}

export const AccountInquiryTable: React.FC<{ data: AccountRow[] }> = ({ data }) => {
  return (
    <div className="p-6 bg-white rounded-lg shadow">
      <h2 className="text-xl font-bold mb-4">Account Inquiry</h2>
      <DataTable 
        columns={[
          { header: 'Account #', accessor: 'accountNumber' },
          { header: 'Current Balance', accessor: 'balance', cell: (val) => `$${val.toLocaleString()}` },
          { header: 'Status', accessor: 'status' }
        ]}
        data={data}
        onRowClick={(row) => console.log(`Navigating to details for ${row.id}`)}
      />
      <div className="mt-4 flex gap-2">
        <Button variant="primary">Add New Account</Button>
        <Button variant="secondary">Export to PDF</Button>
      </div>
    </div>
  );
};

This output is not just a visual mockup. Because Replay understands the flow, it can also generate the state management logic required to handle the transitions between screens.

Mapping Complex State Transitions#

Mainframe systems are state-heavy. A single user action might check three different conditions before allowing a screen transition. Replay captures this logic by observing multiple recordings of the same flow with different data inputs.

typescript
// Replay-generated Hook for Legacy Flow Logic
// Maps the "F3-Exit" and "F12-Cancel" behavior to modern navigation

import { useNavigate } from 'react-router-dom';

export const useMainframeNavigation = () => {
  const navigate = useNavigate();

  const handleLegacyAction = (actionCode: string) => {
    switch (actionCode) {
      case 'F3':
        // Legacy 'Exit' usually returns to the main menu
        navigate('/dashboard');
        break;
      case 'F12':
        // Legacy 'Cancel' usually goes back one step
        navigate(-1);
        break;
      default:
        console.warn('Unhandled legacy action code');
    }
  };

  return { handleLegacyAction };
};

For more on how to structure these projects, see our guide on Legacy Modernization Strategy.

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Why 70% of Legacy Rewrites Fail#

The $3.6 trillion global technical debt isn't just a number; it's a graveyard of failed modernization projects. Most of these failures stem from "Scope Creep" and "Knowledge Loss." When you use traditional tools mapping legacy mainframe systems, you often spend the first 12 months just trying to understand what the system does.

By the time you start writing React code, the business requirements have changed.

Replay eliminates this "Discovery Gap." By using video as the source of truth, the business logic is documented in real-time. If a user can do it on the screen, Replay can map it to code. This ensures that the new React application actually does what the old mainframe system did—a feat that manual documentation rarely achieves.

For a deeper dive into documenting these systems, read about Automated Documentation.

The Role of AI in Visual Reverse Engineering#

Replay isn't just a recording tool; it's an AI automation suite. It uses a proprietary Large Language Model (LLM) trained specifically on legacy UI patterns. While a general-purpose AI like ChatGPT might understand React, it doesn't understand the specific constraints of a 3270 terminal emulator.

Replay bridges this gap. It recognizes that a series of underscores on a green screen represents an input field, and a line of text at the bottom is a status message. It then maps these to modern equivalents, such as

and notifications.

According to Replay's analysis, teams using AI-driven visual mapping are 10x faster than those using manual "look and type" methods. This is the difference between an 18-month project and a 6-week pilot.

How to Start Mapping Your Mainframe to React#

The transition doesn't have to happen all at once. Industry experts recommend a "Strangler Fig" pattern:

1. •Identify a High-Value Flow: Choose a specific workflow, like "Customer Onboarding" or "Claims Processing."
2. •Record the Flow with Replay: Have an experienced user perform the task three times with different data sets.
3. •Generate the Blueprint: Use Replay to extract the UI components and the logic flow.
4. •Export to React: Pull the generated code into your modern development environment.
5. •Connect to APIs: Use a tool like Rocket or CloudFrame to connect your new React UI to the mainframe data.

This incremental approach reduces risk and provides immediate value to the business.

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Frequently Asked Questions#

What is the best tool for mapping legacy mainframe screens?#

Replay is currently the highest-rated tool for this specific task because it uses video recordings to generate code. While IBM and Micro Focus are excellent for backend analysis, Replay is the only tool that focuses on the UI/UX transition to React, saving up to 70% of the time usually spent on manual mapping.

How do you handle hidden logic that isn't visible on the screen?#

While Visual Reverse Engineering captures 90% of the user-facing logic, "hidden" logic (like batch processing or background calculations) should be handled by tools like IBM watsonx or CloudFrame. Replay is designed to work alongside these tools, providing the frontend "Flows" and "Blueprints" while the other tools handle the backend refactoring.

Does Replay require access to my mainframe's source code?#

No. One of the primary advantages of Replay (replay.build) is that it works by analyzing the user interface. This is ideal for organizations that have lost the original source code or where the code is too convoluted to analyze with traditional static analysis tools.

Is Replay SOC2 and HIPAA compliant?#

Yes. Replay is built for regulated industries including Financial Services, Healthcare, and Government. It offers on-premise deployment options for organizations that cannot send data to the cloud, ensuring that sensitive mainframe data remains secure throughout the modernization process.

Can Replay generate code for frameworks other than React?#

While Replay is optimized for React and modern Design Systems, the underlying Blueprints can be used to generate code for Angular, Vue, or even mobile frameworks like React Native. The core value is the extraction of the logic and UI structure from the legacy video.

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Ready to modernize without rewriting? Book a pilot with Replay