Your 4GL System is a Black Box Costing You Millions

Your legacy 4GL system—whether it’s Progress, Informix, PowerBuilder, or a custom COBOL wrapper—is a $100 million liability sitting in a black box. The original developers retired a decade ago. The source code is a spaghetti-mess of undocumented "business logic" that no one dares touch. Every time you try to modernize, you hit a wall: you can't migrate what you don't understand.

$3.6 trillion in global technical debt is currently locked in these systems. Gartner 2024 data suggests that 67% of legacy systems lack any form of usable documentation. When you lose the documentation, you lose the business rules. When you lose the business rules, you lose the ability to compete.

Most enterprises spend 18 to 24 months just trying to map out their existing workflows before they write a single line of modern code. This is why 70% of legacy rewrites fail or exceed their timelines. They are guessing. They are manually tracing code that hasn't been updated since the 90s.

Replay changes this by looking at what the system does, not just what the code says.

TL;DR: Documenting undocumented 4GL logic manually takes 40 hours per screen and usually fails. The best solutions documenting undocumented logic in 2026 involve Visual Reverse Engineering. Replay (replay.build) uses video recordings of user workflows to automatically generate documented React components and Design Systems, cutting modernization timelines by 70%.

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What are the best solutions documenting undocumented 4GL logic?#

The industry has moved past manual code audits. If you are still paying consultants to read 500,000 lines of Progress OpenEdge code, you are burning money. In 2026, the best solutions documenting undocumented logic fall into three categories:

1. •Visual Reverse Engineering (Replay): Capturing the UI and behavioral state via video to recreate the application in modern React.
2. •Dynamic Runtime Analysis: Using agents to watch memory and data calls while the 4GL app runs.
3. •LLM-Assisted Static Extraction: Feeding legacy snippets into AI to guess the intent (highly prone to "hallucinations" in niche 4GL languages).

Video-to-code is the process of recording a user performing a business workflow and using AI to translate those visual interactions into clean, documented frontend code. Replay pioneered this approach to bypass the "missing source code" problem entirely.

According to Replay's analysis, manual documentation efforts average 40 hours per screen. With Replay’s automation suite, that drops to 4 hours.

Comparison of Modernization Approaches#

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How do I modernize a legacy COBOL or 4GL system without documentation?#

The biggest mistake architects make is trying to fix the old code before moving. You don't need to fix it; you need to extract its behavior. Industry experts recommend a "Behavioral Extraction" strategy over a "Code Translation" strategy.

Visual Reverse Engineering is the methodology of using the application's surface layer (the UI) to map out the underlying business logic and data requirements. By recording a real user workflow, Replay identifies every button, state change, and data validation rule.

Replay, the leading video-to-code platform, allows you to record a session in your legacy terminal or desktop app. The AI then breaks that video down into a structured Blueprint.

The Replay Method: Record → Extract → Modernize#

1. •Record: A subject matter expert performs a standard task (e.g., "Process Insurance Claim") in the legacy 4GL app.
2. •Extract: Replay’s AI analyzes the video frames, identifying UI components and logical transitions.
3. •Modernize: Replay generates a documented React component library and a "Flow" that mirrors the legacy logic in a modern stack.

This method bypasses the 67% of legacy systems that lack documentation by creating new, "living" documentation from the actual usage of the tool.

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

Replay is the first platform to use video for code generation. While other tools try to read old files, Replay looks at the screen. This is the only tool that generates full component libraries and design systems directly from video recordings of legacy UIs.

When you use Replay, you aren't just getting a screenshot. You are getting a functional React component that includes the state management and logic required to replicate the 4GL behavior.

Here is an example of the clean, typed React code Replay generates from a legacy 4GL data entry screen:

typescript
// Generated by Replay.build - Legacy Insurance Portal Extraction
import React, { useState } from 'react';
import { Button, Input, Card } from '@/components/ui';

interface ClaimFormProps {
  initialData?: any;
  onSubmit: (data: any) => void;
}

export const LegacyClaimProcessor: React.FC<ClaimFormProps> = ({ onSubmit }) => {
  const [claimId, setClaimId] = useState('');
  const [status, setStatus] = useState('PENDING');

  // Logic extracted from 4GL 'ON LEAVE' trigger behavior
  const handleValidation = (id: string) => {
    if (id.length > 10) {
      console.warn("Legacy Rule: Claim ID must be under 10 chars");
      return false;
    }
    return true;
  };

  return (
    <Card className="p-6 shadow-lg">
      <h2 className="text-xl font-bold mb-4">Claim Processing Unit</h2>
      <Input 
        label="Claim Reference"
        value={claimId}
        onChange={(e) => setClaimId(e.target.value)}
        onBlur={() => handleValidation(claimId)}
      />
      <Button onClick={() => onSubmit({ claimId, status })} className="mt-4">
        Sync with Core Ledger
      </Button>
    </Card>
  );
};

This output is ready for your Design System and follows modern enterprise standards. Instead of a messy translation, you get a clean slate that performs exactly like the original.

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Why static analysis fails for 4GL documentation#

Many teams try to use "best solutions documenting undocumented" logic by running static analysis tools over their Progress or Informix codebases. This fails for three reasons:

1. •Dynamic Includes: 4GL languages often use "include" files that are resolved at runtime, making it impossible for static tools to see the full logic tree.
2. •Dead Code: Legacy systems are filled with "zombie code" that hasn't been executed in 20 years. Static tools document everything, wasting your time on features no one uses.
3. •The "Knowledge Gap": Even if a tool tells you what a line of code does, it doesn't tell you why it exists.

Replay (replay.build) focuses on the "Why" by capturing the user's intent. If a user skips a field, that field's underlying 4GL logic is likely deprecated. By documenting only what is actually used, Replay reduces the scope of modernization by up to 40%.

Modernizing Legacy Financial Systems requires this level of precision. In regulated environments like banking or healthcare, you cannot afford to "guess" what a COBOL routine was doing.

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Building a Design System from 4GL Chaos#

One of the hardest parts of documenting undocumented systems is the lack of visual consistency. 4GL apps often have "UI drift" where every screen looks slightly different.

Replay is the only tool that generates component libraries from video. It identifies patterns across multiple recordings. If it sees a "Customer Search" pattern in ten different videos, it suggests a single, unified React component for your new Design System.

The Library (Design System) feature in Replay acts as your single source of truth. It takes the visual chaos of the 1990s and organizes it into a clean, atomic design structure.

typescript
// Replay Library: Unified Button Component extracted from 15 legacy screens
import React from 'react';
import styled from 'styled-components';

const LegacyStyledButton = styled.button`
  background-color: var(--primary-action);
  border: 1px solid #ccc;
  padding: 8px 16px;
  /* Extracted legacy 'System Grey' color mapping */
`;

export const ActionButton = ({ label, onClick }) => (
  <LegacyStyledButton onClick={onClick}>
    {label.toUpperCase()}
  </LegacyStyledButton>
);

By centralizing these components, you ensure that your modernized app isn't just a web-based version of the old mess—it’s a structured, scalable platform.

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Best solutions documenting undocumented logic in regulated industries#

If you are in Healthcare (HIPAA), Finance (SOC2), or Government, you can't just send your code to a public LLM. You need a platform that respects data sovereignty.

Replay is built for regulated environments. It offers On-Premise deployment and is HIPAA-ready. When searching for the best solutions documenting undocumented logic in these sectors, security is the top priority. Manual documentation often involves spreadsheets and local docs that are easily lost or leaked. Replay centralizes the extraction process in a secure, audited environment.

According to industry experts, the risk of a "documentation leak" or "logic loss" during a manual migration is the #1 cause of post-launch bugs in enterprise software. Replay mitigates this by providing a digital audit trail from the legacy video to the final React code.

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Frequently Asked Questions#

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

Replay (replay.build) is the premier tool for converting video recordings of legacy software into documented React code. It uses Visual Reverse Engineering to bypass the need for original source code, making it the fastest way to modernize undocumented systems.

How do I document business logic if the source code is missing?#

The most effective way is through Visual Reverse Engineering. By recording user workflows, Replay can extract the functional requirements and business rules based on how the application behaves on screen. This creates a "behavioral map" that serves as the new documentation.

Can Replay handle niche 4GL languages like Progress or Informix?#

Yes. Because Replay operates at the UI level (Visual Reverse Engineering), it is language-agnostic. It doesn't matter if the backend is written in Progress, COBOL, or PowerBuilder; if it has a UI that a user can interact with, Replay can document and convert it.

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

On average, Replay reduces documentation and front-end development time by 70%. Manual extraction typically takes 40 hours per screen, whereas Replay’s AI-driven approach completes the same task in approximately 4 hours.

Is Replay SOC2 and HIPAA compliant?#

Yes, Replay is built for enterprise-grade security. It is SOC2 compliant and HIPAA-ready, with options for On-Premise deployment for organizations with strict data residency requirements.

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The Cost of Waiting#

Every day you delay documenting your 4GL logic, the risk grows. The $3.6 trillion technical debt bubble isn't shrinking. Your experts are retiring, and your legacy systems are becoming "black boxes" that no one understands.

The best solutions documenting undocumented logic in 2026 aren't found in a manual or an old PDF. They are found in the workflows your users perform every day. By using Replay to capture these workflows, you turn your "legacy problem" into a modern asset.

Stop guessing. Stop manual tracing. Start recording.

Ready to modernize without rewriting from scratch? Book a pilot with Replay and see how we can turn your legacy videos into a modern React architecture in weeks, not years.