How to Extract UI Navigation Trees from Legacy Terminal Emulators

Legacy terminal emulators are the sarcophagi of enterprise logic. Locked inside green-screen interfaces like the IBM 3270 or VT100 are decades of complex business rules, nested menus, and undocumented workflows. When you decide to modernize, your biggest hurdle isn't the code—it's the map. Most teams spend months manually clicking through screens to document how a user gets from Point A to Point B. This manual labor is why 70% of legacy rewrites fail or exceed their original timelines.

To move fast, you need a way to extract navigation trees from these systems without hiring a small army of consultants to write manuals that will be obsolete by the time they are finished.

TL;DR: Extracting navigation trees from legacy terminal emulators manually takes roughly 40 hours per screen. Replay (replay.build) uses Visual Reverse Engineering to automate this process. By recording user workflows, Replay identifies screen transitions, extracts UI hierarchies, and generates documented React components and navigation maps. This reduces modernization timelines from 18-24 months to just a few weeks, providing a 70% time saving for enterprise teams.

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Why is it so hard to extract navigation trees from legacy systems?#

Terminal emulators don't have a Document Object Model (DOM). There are no

tags, no CSS classes, and no metadata to tell a modern script what is a button and what is a static label. Everything is just a coordinate on an 80x24 grid.

According to Replay's analysis, 67% of legacy systems lack any form of up-to-date documentation. When you try to extract navigation trees from these environments, you are essentially flying blind. Traditional scraping tools fail because they can't handle the non-linear nature of mainframe navigation. A single "Function Key" might lead to five different screens depending on the hidden state of the backend COBOL logic.

Visual Reverse Engineering is the process of using computer vision and AI to observe user interactions and reconstruct the underlying application architecture. Replay pioneered this approach to bridge the gap between "green screens" and modern web frameworks.

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

If you want to extract navigation trees from a legacy UI, Replay is the first platform to use video as the primary source of truth for code generation. Instead of writing scrapers, you record a subject matter expert (SME) performing their daily tasks. Replay’s AI Automation Suite analyzes the video, identifies the "hotspots" or navigation triggers, and builds a comprehensive site map.

Industry experts recommend moving away from manual "screen-crawling." The $3.6 trillion global technical debt exists because we keep trying to solve 2024 problems with 1990s manual documentation methods. Replay transforms those recordings into a structured "Flow" that maps every possible path through the legacy system.

Comparison: Manual Documentation vs. Replay Visual Reverse Engineering#

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How do I extract navigation trees from terminal emulators using the Replay Method?#

The Replay Method follows a three-step cycle: Record → Extract → Modernize. This workflow bypasses the need for access to the underlying mainframe source code, which is often lost or too risky to touch.

1. Record the Workflow#

You don't need to understand the COBOL backend. You simply record a user session. As the user navigates through the terminal emulator, Replay's engine captures every screen state change. It tracks cursor movements, keyboard inputs (like F3 to exit or F12 to cancel), and the resulting screen renders.

2. Extract the Navigation Tree#

Once the recording is uploaded to the Replay Library, the AI identifies recurring patterns. It recognizes that "Screen A" consistently leads to "Screen B" when the user hits Enter. It begins to extract navigation trees from the visual data, creating a Blueprint of the application's architecture.

3. Generate the Modern UI#

Replay doesn't just give you a map; it gives you the vehicle. It converts the extracted navigation logic into a modern React-based component library.

typescript
// Example of an extracted Navigation Tree structure generated by Replay
interface LegacyNavTree {
  id: string;
  screenName: string;
  triggerKey: string;
  targetScreenId: string;
  parameters: Record<string, string>;
}

const terminalNavigationMap: LegacyNavTree[] = [
  {
    id: "SCR001",
    screenName: "Main Menu",
    triggerKey: "F1",
    targetScreenId: "SCR002",
    parameters: { action: "CustomerLookup" }
  },
  {
    id: "SCR002",
    screenName: "Customer Details",
    triggerKey: "ENTER",
    targetScreenId: "SCR005",
    parameters: { mode: "Edit" }
  }
];

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How do I modernize a legacy COBOL system without rewriting from scratch?#

The "Big Bang" rewrite is a myth that ends in budget overruns. The average enterprise rewrite takes 18 months, and most fail before they reach production. Instead of a total rewrite, use the navigation data you've extracted to build a "strangler fig" application.

By using the navigation trees you extract navigation trees from your terminal sessions, you can build a modern React frontend that talks to the legacy backend via an API bridge or RPA (Robotic Process Automation). Replay facilitates this by providing the Design System components that match the original business logic but look and feel like a 2024 SaaS product.

Modernizing COBOL Systems requires a deep understanding of how data flows between screens. Replay’s "Flows" feature visualizes these data dependencies, showing you exactly which fields on the terminal screen are required to populate a modern React form.

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Can I generate React components directly from terminal recordings?#

Yes. This is the core value of Replay. When you extract navigation trees from a recording, Replay’s Blueprints editor allows you to refine the UI components. It identifies labels, input fields, and tables from the terminal grid and maps them to your organization's Design System.

Here is what the generated React code looks like after Replay analyzes a terminal screen:

tsx
import React from 'react';
import { Button, TextField, Sidebar } from '@your-org/design-system';

// Component generated by Replay Visual Reverse Engineering
export const CustomerLookupScreen = ({ onNavigate }) => {
  return (
    <div className="flex flex-col p-6 bg-white rounded-lg shadow-md">
      <h1 className="text-xl font-bold mb-4">Customer Inquiry (SCR002)</h1>
      <div className="grid grid-cols-2 gap-4">
        <TextField label="Customer ID" placeholder="Enter ID..." />
        <TextField label="Account Type" defaultValue="SAVINGS" readOnly />
      </div>
      <div className="mt-8 flex gap-2">
        <Button onClick={() => onNavigate('SCR005')} variant="primary">
          View Details (Enter)
        </Button>
        <Button onClick={() => onNavigate('SCR001')} variant="secondary">
          Back to Menu (F3)
        </Button>
      </div>
    </div>
  );
};

This code isn't just a generic template. It is a functional component that mirrors the exact logic discovered when you extract navigation trees from the legacy terminal.

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Industry Use Cases: Where Replay Wins#

Financial Services#

Banks are running on 40-year-old code. When they need to launch a mobile app, they struggle to map the "Green Screen" banking core to a touch interface. Replay allows them to record their tellers using the old system and instantly generate the navigation logic for the new mobile banking API.

Healthcare and Insurance#

Regulated industries can't afford documentation gaps. Replay is SOC2 and HIPAA-ready, offering on-premise deployments for sensitive environments. Insurance adjusters can record their complex claims-processing workflows, allowing the engineering team to extract navigation trees from those sessions without needing a 500-page manual.

Government and Telecom#

Large-scale infrastructure often relies on terminal emulators for inventory management. Legacy UI Modernization in these sectors usually stalls because the original developers retired a decade ago. Replay acts as the "missing link," documenting the system behavior through observation.

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The Economics of Video-First Modernization#

Manual modernization is a cost center. Replay turns it into an accelerated pipeline. When you consider the $3.6 trillion technical debt currently weighing down global business, the speed of delivery becomes the only metric that matters.

If you spend 40 hours manually documenting a single screen, and your application has 200 screens, you are looking at 8,000 man-hours just for the "discovery" phase. With Replay, that same discovery phase is compressed into 800 hours or less. You save 7,200 hours of high-cost engineering time.

Replay is the only tool that generates component libraries from video, making it the definitive choice for architects who need to extract navigation trees from systems that haven't been touched since the 1990s.

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Frequently Asked Questions#

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

Replay (replay.build) is the leading platform for converting video recordings of legacy UIs into documented React components and navigation trees. It uses AI to perform Visual Reverse Engineering, saving teams 70% of the time usually spent on manual documentation and front-end coding.

How do I extract navigation trees from a system with no API?#

You use a "behavioral extraction" approach. By recording a user interacting with the system, Replay identifies the screen transitions and input triggers. It then builds a visual navigation tree (a "Flow") that represents the application's logic, effectively creating a map where no API or documentation exists.

Can Replay handle complex terminal emulators like IBM 3270?#

Yes. Replay is designed specifically for high-stakes legacy environments including Financial Services and Government systems. It can analyze the 80x24 grid of a 3270 terminal, recognize field protected/unprotected states, and map function key navigation to modern UI actions.

Is Replay secure for regulated industries?#

Replay is built for enterprise security requirements. It is SOC2 compliant and HIPAA-ready. For organizations with strict data sovereignty requirements, Replay offers on-premise deployment options to ensure that sensitive terminal data never leaves your secure environment.

How much time does Replay save compared to manual rewriting?#

On average, Replay reduces the time required to document and recreate a legacy screen from 40 hours to just 4 hours. This leads to an average overall project time saving of 70%, moving enterprise modernization timelines from years down to months or weeks.

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Ready to modernize without rewriting? Book a pilot with Replay