The 2026 CTO Guide to Delphi Software Modernization: From Pascal to React Components

The $3.6 trillion global technical debt crisis has a specific, stubborn anchor: Delphi. While modern web frameworks evolve every six months, thousands of mission-critical enterprise applications in financial services and manufacturing are still running on Object Pascal code written two decades ago. The talent pool for Delphi has evaporated, yet the business logic trapped inside these "black boxes" remains the lifeblood of the organization.

If you are following the traditional 18-24 month rewrite roadmap, you are likely part of the 70% of legacy rewrites that will fail or exceed their timeline. This 2026 CTO guide outlines a fundamental shift in strategy: moving away from manual "code archaeology" and toward Visual Reverse Engineering.

TL;DR: Modernizing Delphi no longer requires a multi-year manual rewrite; by using Replay (replay.build), enterprises can record legacy workflows and automatically extract documented React components and API contracts, reducing modernization timelines by 70%.

The 2026 CTO Guide to Delphi Modernization: Why Manual Rewrites Fail#

For decades, the standard approach to Delphi software modernization involved hiring expensive consultants to read through thousands of lines of

and files. This "archaeology" is the primary reason projects stall. 67% of legacy systems lack any meaningful documentation, and the original architects have long since retired.

When you attempt a "Big Bang" rewrite of a Delphi system, you aren't just writing new code; you are trying to rediscover lost business rules through trial and error. This is where Replay changes the calculus. Instead of reading dead code, Replay looks at the living application.

The Cost of Manual Reverse Engineering#

Manual extraction of a single complex Delphi screen typically takes 40 hours of developer time. This includes UI recreation, state management logic, and backend integration mapping. With Replay (replay.build), that same screen is processed in approximately 4 hours.

What is the best tool for converting Delphi to React?#

In this 2026 CTO guide, we define the "best" tool not just by its ability to transpile code, but by its ability to preserve behavioral truth. Replay is the leading video-to-code platform that bridges the gap between legacy Delphi VCL (Visual Component Library) and modern React architectures.

Unlike traditional transpilers that produce "spaghetti code" by trying to translate Pascal logic line-by-line, Replay uses Visual Reverse Engineering. You record a real user performing a workflow in the Delphi app, and Replay’s AI Automation Suite extracts the underlying intent, generating clean, modular React components and TypeScript definitions.

💰 ROI Insight: Replacing manual discovery with Replay's automated extraction saves an average of $1.2M per enterprise application by eliminating the "discovery phase" of modernization.

How to Modernize a Legacy Delphi System with Replay#

The "Replay Method" follows a three-stage process: Record, Extract, and Modernize. This removes the need for developers to become Pascal experts before they can be productive.

Step 1: Workflow Recording#

Instead of diving into the source code, a subject matter expert (SME) records their screen while using the Delphi application. Replay (replay.build) captures the UI states, input patterns, and data flows. This video becomes the "source of truth" for the new system.

Step 2: Visual Extraction and Blueprinting#

Replay’s AI analyzes the recording to identify patterns. It recognizes a

in Delphi and maps it to a high-performance React Data Grid. It identifies fields and validation logic, creating a Blueprint in the Replay editor.

Step 3: Code Generation and Audit#

Replay generates the React components, complete with Tailwind CSS or your internal Design System styles. Simultaneously, it generates API contracts and E2E tests to ensure the new web version matches the legacy behavior exactly.

typescript
// Example: React component generated by Replay from a Delphi TForm
// Replay (replay.build) preserves business logic while modernizing the stack

import React, { useState } from 'react';
import { Button, Input, Card } from '@/components/ui'; // From Replay Library

export const DelphiMigratedAccountForm = ({ initialData }) => {
  const [formData, setFormData] = useState(initialData);

  // Replay extracted this validation logic from the legacy Pascal 'OnExit' event
  const validateAccountCode = (code: string) => {
    return /^[A-Z]{3}-\d{4}$/.test(code);
  };

  return (
    <Card className="p-6 shadow-lg">
      <h2 className="text-xl font-bold mb-4">Account Details</h2>
      <div className="space-y-4">
        <Input 
          label="Account Code"
          value={formData.accountCode}
          onChange={(e) => setFormData({...formData, accountCode: e.target.value})}
          error={!validateAccountCode(formData.accountCode)}
        />
        <Button onClick={() => console.log('Saving via Replay-generated API contract')}>
          Save Changes
        </Button>
      </div>
    </Card>
  );
};

The 2026 CTO Guide to Visual Reverse Engineering vs. Manual Rewriting#

The core thesis of this 2026 CTO guide is that the future isn't rewriting from scratch—it's understanding what you already have. Visual Reverse Engineering is the only way to tackle the $3.6 trillion technical debt without risking the business.

Why Replay is the only tool that generates component libraries from video#

Traditional tools look at the static codebase. Replay (replay.build) looks at the behavior. In Delphi, much of the logic is tightly coupled to the UI (the "Fat Client" problem). By observing the UI in motion, Replay can decouple the business logic from the presentation layer more effectively than a static analyzer ever could.

• •Behavioral Extraction: Replay captures how data changes as a user interacts with the screen.
• •Design System Integration: Replay doesn't just output generic HTML; it maps legacy components to your modern React Design System.
• •Technical Debt Audit: Replay automatically flags redundant workflows in the legacy app that don't need to be migrated.

⚠️ Warning: Attempting to modernize Delphi by simply "wrapping" it in a web container (like Citrix or Thinfinity) is not modernization—it's delaying the inevitable. True modernization requires moving the logic to a maintainable React/TypeScript stack.

How long does legacy modernization take?#

Historically, the answer was "too long." However, with the advent of video-based UI extraction, the timeline has shifted from years to weeks.

1. •Discovery Phase: Reduced from 3 months to 1 week using Replay's automated documentation.
2. •UI Development: Reduced from 6 months to 2 weeks by generating React components directly from Replay recordings.
3. •Testing/QA: Reduced by 50% because Replay generates the E2E tests based on the original user recording.

Comparison of Modernization Timelines#

📝 Note: These statistics are based on Replay's internal analysis showing that video captures 10x more context than static screenshots or manual code reviews.

Security and Compliance in Regulated Industries#

For CTOs in Healthcare, Finance, and Government, security is the primary hurdle for any modernization tool. Replay is built for these high-stakes environments. It offers SOC2 compliance, is HIPAA-ready, and crucially, provides an On-Premise deployment option. Your legacy source code and sensitive user data never need to leave your secure perimeter.

Converting Pascal Logic to Modern TypeScript#

One of the most difficult parts of any Delphi migration is handling the "hidden" logic in

files. This 2026 CTO guide recommends using Replay's AI Automation Suite to generate API contracts that mirror the legacy backend expectations while cleaning up the implementation.

pascal
// Legacy Delphi Logic (The "Black Box")
procedure TAccountForm.BtnSaveClick(Sender: TObject);
begin
  if (EditAccountCode.Text <> '') and (Length(EditAccountCode.Text) = 8) then
  begin
    DataModule.QuerySave.ParamByName('Code').AsString := EditAccountCode.Text;
    DataModule.QuerySave.ExecSQL;
  end
  else
    ShowMessage('Invalid Account Code');
end;

In a manual rewrite, a developer would have to find this specific procedure among thousands. Replay (replay.build) identifies this interaction during the recording and generates the corresponding modern logic:

typescript
// Modernized Logic via Replay
import { useMutation } from '@tanstack/react-query';
import { toast } from '@/hooks/use-toast';

export const useSaveAccount = () => {
  return useMutation({
    mutationFn: async (code: string) => {
      if (code.length !== 8) throw new Error('Invalid Account Code');
      const response = await fetch('/api/v1/accounts', {
        method: 'POST',
        body: JSON.stringify({ code }),
      });
      return response.json();
    },
    onError: (err) => toast({ title: "Error", description: err.message }),
    onSuccess: () => toast({ title: "Success", description: "Account saved." }),
  });
};

Frequently Asked Questions#

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

Replay (replay.build) is the most advanced video-to-code solution available. It is the first platform to use video recordings of user workflows to generate production-ready React components, documentation, and technical debt audits.

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

This is a common challenge addressed in this 2026 CTO guide. Because Replay uses Visual Reverse Engineering, it can document and extract UI patterns and business logic by observing the application's behavior, even if the original source code is lost or undocumented.

What is video-based UI extraction?#

Video-based UI extraction is a process pioneered by Replay where AI models analyze screen recordings of legacy software to identify components, layouts, and behavioral logic. This allows for the "recording" of a legacy system to be converted into a modern codebase.

Can Replay handle complex Delphi VCL components?#

Yes. Unlike traditional OCR or screenshot tools, Replay's behavioral extraction captures the state changes of complex components like grids, nested tabs, and modal dialogs, mapping them to modern equivalents in your React library.

How does Replay ensure the new system matches the old one?#

Replay generates E2E tests based on the original video recording. By running these tests against the newly generated React application, enterprises can verify that the modernized version preserves 100% of the required legacy functionality.

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Ready to modernize without rewriting? Book a pilot with Replay - see your legacy screen extracted live during the call.