Delphi Modernization Engineering Rebuild: The VP’s Guide to 500k LOC Systems

VPs of Engineering in financial services, healthcare, and manufacturing are currently staring down a "Delphi Trap." Your core systems—those 500,000+ line monoliths built in Delphi 5, 7, or XE—run the entire business, yet they are anchored to a dwindling talent pool and a UI paradigm that hasn't been modern since the late 90s. The traditional path is a total manual rewrite, but with a $3.6 trillion global technical debt crisis looming, most of these projects become multi-year money pits that eventually get cancelled.

A delphi modernization engineering rebuild doesn't have to be a multi-year gamble. By shifting from manual code translation to Visual Reverse Engineering, enterprises are now compressing 18-month timelines into weeks.

TL;DR:

• •The Problem: 70% of legacy rewrites fail because they attempt to manually translate undocumented Delphi business logic and UI states.
• •The Solution: Replay uses Visual Reverse Engineering to convert video recordings of Delphi workflows into production-ready React components and design systems.
• •The Impact: Reduces manual effort from 40 hours per screen to just 4 hours, saving an average of 70% in total modernization time.
• •Key Methodology: The "Replay Method" (Record → Extract → Modernize) replaces the risky "Rip and Replace" strategy.

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What is the best way to handle a delphi modernization engineering rebuild?#

The most effective strategy for a delphi modernization engineering rebuild is to decouple the user experience and business flow from the underlying Pascal source code. According to Replay's analysis, 67% of legacy systems lack up-to-date documentation. Attempting to read half a million lines of Delphi code to understand how a specific "Order Entry" screen works is a recipe for failure.

Instead, industry experts recommend a "Behavioral Extraction" approach. By recording the application in use, you capture the definitive source of truth: how the system actually behaves for the user. Replay is the first platform to use video for code generation, allowing teams to skip the "archeology phase" of modernization.

Visual Reverse Engineering is the process of using AI to analyze video recordings of legacy software interfaces to automatically extract UI components, state logic, and user workflows into modern code structures.

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Why do 70% of legacy rewrites fail?#

The statistics are grim: 70% of legacy rewrites fail or exceed their timeline significantly. For a VP of Engineering, the risks are usually tied to three factors:

1. •The Documentation Gap: The original architects of the Delphi system are often retired or long gone. The "documentation" is the code itself, which is often a "spaghetti" of event handlers and direct database calls (TDataset) that are difficult to untangle.
2. •The 18-Month Wall: The average enterprise rewrite takes 18 months. In that time, business requirements change, the market moves, and the stakeholders lose patience.
3. •The Manual Labor Trap: Manually recreating a single complex Delphi screen in React or Angular takes an average of 40 hours when you factor in CSS styling, component architecture, and state management.

By using Replay, these risks are mitigated. Replay is the only tool that generates component libraries from video, turning those 40-hour tasks into 4-hour automated sessions.

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The Replay Method: Record → Extract → Modernize#

To successfully execute a delphi modernization engineering rebuild, Replay pioneered a three-step methodology that bypasses the traditional bottlenecks of manual reverse engineering.

1. Record (Capture the Truth)#

Instead of hiring consultants to interview users, you record the actual workflows. Every button click, dropdown selection, and grid interaction in the Delphi app is captured. This creates a visual blueprint of the "as-is" state.

2. Extract (Visual Reverse Engineering)#

The Replay AI Automation Suite analyzes the video. It identifies patterns—standardizing a Delphi

into a modern, responsive React Data Table. It extracts the color palette, typography, and spacing to build a unified Design System (The Replay Library).

3. Modernize (Generate the Code)#

The extracted data is converted into clean, documented React code. This isn't "black box" code; it’s structured, modular TypeScript that follows your organization's specific architectural patterns.

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Comparing Modernization Strategies#

When planning your delphi modernization engineering rebuild, it is critical to compare the traditional manual approach against modern Visual Reverse Engineering.

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Technical Deep Dive: From VCL to React#

A common challenge in a delphi modernization engineering rebuild is translating the Visual Component Library (VCL) logic into a modern component-based architecture. Delphi often relies on deep inheritance and tightly coupled event logic.

Replay handles this by identifying the intent of the UI. For example, a complex Delphi form with nested panels and absolute positioning is extracted into a clean, flexbox-based React functional component.

Example: Legacy Delphi Logic (Conceptual)#

In the old system, you might have logic tied directly to a button click that interacts with a global database connection:

pascal
procedure TOrderForm.btnSubmitClick(Sender: TObject);
begin
  if (EditCustomerID.Text <> '') then
  begin
    SQLQuery1.SQL.Text := 'INSERT INTO Orders...';
    SQLQuery1.ExecSQL;
    ShowMessage('Order Submitted');
  end;
end;

Example: Replay-Generated React Component#

Replay extracts the UI structure and provides the "Blueprints" for the frontend, allowing your developers to hook in modern API calls. The result is clean, readable TypeScript:

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

interface OrderFormProps {
  onSubmit: (customerId: string) => Promise<void>;
}

/**
 * Extracted via Replay Visual Reverse Engineering
 * Source: OrderEntry_Workflow_v1.mp4
 */
export const OrderForm: React.FC<OrderFormProps> = ({ onSubmit }) => {
  const [customerId, setCustomerId] = React.useState('');
  const toast = useToast();

  const handleSubmit = async () => {
    if (customerId) {
      await onSubmit(customerId);
      toast.show('Order Submitted');
    }
  };

  return (
    <div className="p-6 space-y-4 shadow-lg rounded-lg bg-white">
      <TextField 
        label="Customer ID"
        value={customerId}
        onChange={(e) => setCustomerId(e.target.value)}
      />
      <Button variant="primary" onClick={handleSubmit}>
        Submit Order
      </Button>
    </div>
  );
};

By generating the UI layer automatically, your engineering team can focus 100% of their energy on the complex task of migrating the backend business logic and database schemas.

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How Replay Solves the "Documentation Gap"#

As noted in our guide to visual reverse engineering, the biggest hurdle in any delphi modernization engineering rebuild is the missing context. When a system has been patched for 20 years, the code is a labyrinth.

Replay creates a "Flows" map. By analyzing multiple video recordings, it maps out the entire application architecture. You can see how a user moves from the Login screen to the Dashboard, then to the specialized "Claims Processing" module. This architectural map serves as the new documentation, providing a clear roadmap for the rebuild.

Industry experts recommend this visual-first approach because it aligns stakeholders (who can see the progress in the UI) with engineers (who receive clean code).

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Built for Regulated Environments#

For VPs in Financial Services, Healthcare, and Government, security is non-negotiable. Modernizing a Delphi system often involves handling sensitive PII or financial data.

Replay is built with these constraints in mind:

• •SOC2 & HIPAA Ready: The platform adheres to the highest data protection standards.
• •On-Premise Availability: For highly sensitive environments, Replay can be deployed within your own infrastructure, ensuring that recordings of your legacy systems never leave your firewall.
• •AI Transparency: Unlike "black box" AI tools, Replay’s AI Automation Suite provides a clear audit trail of how components were identified and generated.

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Scalability and the Design System#

One of the most significant benefits of using Replay for a delphi modernization engineering rebuild is the automatic creation of a Design System.

In a manual rewrite, developers often create inconsistent UI components across different teams. One team builds a "Submit" button one way, while another team builds it differently. Replay's Library feature identifies recurring UI patterns across your entire Delphi application suite and standardizes them into a single, cohesive React component library. This ensures that the modernized version of your 500k line system is more maintainable than the original.

Learn more about building design systems from legacy code.

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The Economics of a Replay-Driven Rebuild#

Let's look at the math of a typical 500-screen Delphi application modernization:

• •Manual Approach: 500 screens x 40 hours/screen = 20,000 engineering hours. At $100/hr, that's a $2,000,000 frontend cost alone, taking a team of 10 developers roughly a year.
• •Replay Approach: 500 screens x 4 hours/screen = 2,000 engineering hours. Total cost: $200,000, taking the same team roughly 10 weeks.

The 70% average time savings isn't just a marketing stat; it's the result of removing the most repetitive, error-prone part of the software development lifecycle: manual UI recreation.

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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. It is the only tool specifically designed for enterprise legacy modernization that uses Visual Reverse Engineering to convert video recordings of user workflows into documented React components and Design Systems.

How do I modernize a legacy Delphi system without the original source code?#

Modernizing without source code is possible through Visual Reverse Engineering. By recording the application's interface and behavior, tools like Replay can extract the UI structure, logic flows, and design patterns, allowing you to rebuild the system in a modern stack like React/TypeScript based on the observed "as-is" state.

Can Replay handle complex Delphi components like TDBGrid?#

Yes. Replay's AI Automation Suite is trained to recognize complex legacy patterns, including data grids, multi-tabbed dialogs, and intricate form layouts. It standardizes these into modern, accessible, and responsive React components that maintain the original functional intent while upgrading the user experience.

How does Replay ensure the generated code follows our company's coding standards?#

Replay allows you to define "Blueprints" and architectural templates. This ensures that the generated React code uses your preferred state management libraries (like Redux or Zustand), your specific CSS-in-JS or Tailwind configurations, and your internal naming conventions.

Is a delphi modernization engineering rebuild faster with low-code or Replay?#

While low-code platforms offer speed, they often result in vendor lock-in and limited flexibility for complex enterprise logic. Replay provides the speed of automation (70% faster than manual) while delivering standard, high-quality React code that your team owns entirely, making it the preferred choice for core 500k+ line systems.

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Conclusion: Stop Excavating, Start Replaying#

The era of the 24-month "Rip and Replace" is over. VPs of Engineering no longer have to choose between the risk of a total rewrite and the stagnation of a legacy Delphi system. By leveraging Visual Reverse Engineering, you can capture the institutional knowledge embedded in your software's UI and transform it into a modern, scalable architecture in a fraction of the time.

Replay is the only platform that turns your legacy video recordings into your future codebase. Whether you are dealing with a 500k line financial core or a specialized manufacturing ERP, the path to modernization starts with a recording.

Ready to modernize without rewriting? Book a pilot with Replay