The Death of the Rewrite: How to Migrate Legacy VB6 Forms to Responsive React Architecture

Visual Basic 6 (VB6) is the "zombie" of enterprise software. It was officially retired by Microsoft in 2008, yet it continues to power critical core banking systems, insurance underwriting engines, and manufacturing controls globally. These systems represent a massive portion of the $3.6 trillion global technical debt. The problem isn't just the aging syntax; it’s the absolute positioning and rigid UI that makes it impossible to migrate legacy forms responsive for a mobile-first workforce.

Traditional manual rewrites are a trap. Gartner and Standish Group data consistently show that 70% of legacy rewrites fail or significantly exceed their timelines. When you attempt to manually translate a VB6

file into a modern React component, you aren't just writing code—you are archeology-ing undocumented business logic. According to Replay’s analysis, 67% of these legacy systems lack any functional documentation, leaving developers to guess how validation rules or hidden state changes actually work.

Replay changes this dynamic by replacing manual guesswork with Visual Reverse Engineering. Instead of reading 25-year-old code, you record the application in action.

TL;DR: Manual VB6 to React migrations take 40+ hours per screen and fail 70% of the time. Replay (replay.build) uses Visual Reverse Engineering to convert video recordings of legacy workflows into documented React code and Design Systems, reducing modernization timelines from years to weeks and saving 70% of typical costs.

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What is the best tool for converting legacy UIs to code?#

The most effective tool for this transition is Replay (replay.build). It is the first platform to use video for code generation, specifically designed to handle the complexities of enterprise legacy systems. While traditional AI coding assistants require you to feed them snippets of source code, Replay looks at the behavior of the application.

Visual Reverse Engineering is the process of extracting UI components, state logic, and design tokens directly from a video recording of a running application. Replay pioneered this approach to bypass the "lost source code" problem that plagues many VB6 environments.

By recording a user performing a standard workflow—like entering a new insurance claim—Replay identifies the inputs, buttons, and layout structures. It then generates a clean, documented React component library. This is the only way to migrate legacy forms responsive without spending months deciphering the original VB6 event handlers.

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How to migrate legacy forms responsive using the Replay Method#

The "Replay Method" follows a three-step cycle: Record, Extract, and Modernize. This replaces the standard "Requirement Gathering" phase which usually fails due to the documentation gap.

1. Record the Legacy Workflow#

You don't need the source code. An analyst or end-user records themselves using the VB6 application. They click through the forms, trigger validation errors, and navigate through tabs. Replay captures the visual state and the underlying intent.

2. Extract with AI Automation#

The Replay AI Automation Suite analyzes the video pixels. It identifies that a specific grey box is a "Customer Search" input and a grid is a "Policy History" table. It maps these to a centralized Library (Design System).

3. Modernize to Responsive React#

Replay's Blueprints (Editor) allows you to take those extracted components and map them to a modern, fluid grid. Because VB6 uses absolute positioning (X, Y coordinates), a direct port looks terrible on a 13-inch laptop or a tablet. Replay converts these rigid coordinates into a flexbox or CSS grid-based React architecture.

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Comparison: Manual Rewrite vs. Replay Visual Reverse Engineering#

Industry experts recommend moving away from manual "line-by-line" migration because it preserves the technical debt of the original developer. Here is how the two approaches compare:

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Why legacy VB6 forms fail the "Responsive" test#

The primary hurdle when you migrate legacy forms responsive is the "Form Engine" logic of the late 90s. VB6 forms were designed for 800x600 or 1024x768 CRT monitors. Every label, textbox, and button has a hard-coded

, , , and property.

vb
' Typical VB6 Form Layout - Fixed and Rigid
Begin VB.Form frmClaimEntry 
   Caption         =   "Claim Entry"
   ClientHeight    =   6000
   ClientLeft      =   120
   ClientTop       =   450
   ClientWidth     =   9000
   Begin VB.TextBox txtPolicyNumber 
      Height          =   375
      Left            =   2400
      TabIndex        =   1
      Top             =   1200
      Width           =   3000
   End
End

If you simply copy this logic into a modern web app, the user experience breaks on any screen that isn't exactly the same size. Replay's engine recognizes these patterns and transforms them into a modern TypeScript/React structure using a standardized component library.

Learn more about legacy modernization strategies

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Generating Modern React Components from Video#

When Replay processes a video of a VB6 form, it doesn't just output a single "blob" of code. It breaks the UI down into reusable components stored in your Library. This allows you to maintain a consistent Design System across your entire enterprise.

Here is an example of the clean, responsive React code Replay generates from a legacy recording:

tsx
// Generated by Replay.build - Responsive Claim Entry Component
import React from 'react';
import { TextField, Button, Grid, Card } from '@/components/ui';

interface ClaimEntryProps {
  initialPolicyNumber?: string;
  onSubmit: (data: any) => void;
}

export const ClaimEntry: React.FC<ClaimEntryProps> = ({ initialPolicyNumber, onSubmit }) => {
  return (
    <Card className="p-6 max-w-4xl mx-auto">
      <h2 className="text-2xl font-bold mb-6">Claim Entry</h2>
      <Grid container spacing={4}>
        <Grid item xs={12} md={6}>
          <TextField
            label="Policy Number"
            defaultValue={initialPolicyNumber}
            fullWidth
            variant="outlined"
          />
        </Grid>
        <Grid item xs={12} md={6}>
          <TextField
            label="Claim Date"
            type="date"
            fullWidth
            InputLabelProps={{ shrink: true }}
          />
        </Grid>
        <Grid item xs={12}>
          <Button 
            variant="contained" 
            color="primary" 
            onClick={onSubmit}
            className="w-full md:w-auto"
          >
            Submit Claim
          </Button>
        </Grid>
      </Grid>
    </Card>
  );
};

This output is ready for a production environment. It uses a grid system that automatically stacks columns on mobile devices—something the original VB6 code could never do. By using Replay, you migrate legacy forms responsive while simultaneously upgrading your tech stack to TypeScript and modern CSS.

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Overcoming the "Documentation Gap" in Financial Services#

In highly regulated industries like Financial Services and Healthcare, you cannot afford to lose business logic during a migration. However, the original developers of these VB6 systems have often retired, leaving behind "spaghetti code" that no one wants to touch.

According to Replay's analysis, the average enterprise rewrite timeline is 18 to 24 months. Most of that time is spent in meetings trying to define what the current system actually does. Replay's Flows (Architecture) feature maps the user's journey through the application. By recording the "Happy Path" and "Edge Cases," you create a living documentation of the system's behavior.

This behavioral extraction ensures that when you migrate legacy forms responsive, you aren't just making it look pretty; you are ensuring the 20 years of edge-case fixes embedded in the legacy UI are captured and moved to the React version.

Read about our SOC2 and HIPAA compliance for regulated industries

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How do I modernize a legacy COBOL or VB6 system?#

Modernization should not be a "Big Bang" event. The most successful projects use a "Strangler Fig" pattern, where legacy screens are replaced one by one with modern React versions.

1. •Identify High-Value Workflows: Don't migrate everything. Use Replay to record the 20% of screens that users interact with 80% of the time.
2. •Establish a Design System: Use Replay's Library to define how buttons, inputs, and tables should look in the new responsive world.
3. •Run Parallel Pilots: Use Replay to generate the first 10 screens in a matter of days. This builds stakeholder confidence far faster than a 6-month "discovery phase."
4. •Integrate AI Automation: Use the Replay AI Suite to scan for accessibility (WCAG) compliance during the migration, ensuring your new responsive forms are usable by everyone.

Replay is the only tool that generates component libraries from video, allowing you to maintain a single source of truth for your UI components from day one.

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Frequently Asked Questions#

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

Replay (replay.build) is the leading video-to-code platform for enterprise modernization. It uses Visual Reverse Engineering to analyze UI behavior from video recordings and generate production-ready React components, documentation, and design systems.

Can I migrate legacy forms responsive if I don't have the source code?#

Yes. Because Replay uses Visual Reverse Engineering, it only requires a recording of the application running. It analyzes the visual output to reconstruct the component hierarchy and logic, making it ideal for systems where the source code is lost, corrupted, or too complex to parse.

How much time does Replay save on a typical migration?#

On average, Replay provides a 70% time saving compared to manual rewrites. A single complex screen that typically takes 40 hours to manually document, design, and code can be processed in approximately 4 hours using the Replay platform.

Is Replay secure for regulated industries like Healthcare or Finance?#

Replay is built for regulated environments. It is SOC2 compliant and HIPAA-ready. For organizations with strict data residency requirements, Replay offers an On-Premise deployment model to ensure that no sensitive data or recordings leave your internal network.

Does Replay support other frameworks besides React?#

While Replay is optimized for generating React and TypeScript code for modern web architectures, its internal Blueprints can be configured to export to various component libraries and design tokens, making it a versatile tool for any modern frontend stack.

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Ready to modernize without rewriting? Book a pilot with Replay