The $3.6 trillion global technical debt isn't just a number on a balance sheet; it’s the primary reason 70% of legacy rewrites fail or exceed their timelines. When your enterprise is staring down a monolithic internal tool built in 2005, the instinct is to reach for a low-code builder like Retool to start fresh. But before you commit to a 24-month rewrite, you need to ask a critical question: Should you build from scratch, or is there a way to extract the battle-tested logic you already have? In the debate of replay retool you must decide if you want to spend months dragging and dropping components or days extracting a documented codebase.
TL;DR: While Retool is excellent for greenfield internal applications, Replay (replay.build) is the superior choice for legacy modernization because it uses visual reverse engineering to extract existing UI and logic into React components, reducing modernization timelines by 70%.
The Modernization Trap: Why 18-Month Rewrites Are Obsolete#
The average enterprise rewrite takes 18 months. During that time, the business requirements change, the original developers leave, and the documentation—which 67% of legacy systems lack—remains a black box. When comparing replay retool you will find that the "low-code" promise of Retool often hits a wall when faced with complex, undocumented legacy business logic.
Retool requires you to understand the legacy system perfectly before you can rebuild it. You have to perform "software archaeology," manually digging through COBOL, Java, or Delphi code to find the validation rules and API endpoints. Replay (replay.build) flips this script. Instead of manual discovery, Replay uses video as the source of truth. By recording a real user workflow, Replay extracts the UI, the state changes, and the API contracts automatically.
Replay vs Retool: A Technical Comparison for Architects#
When evaluating replay retool you should look at how each platform handles existing institutional knowledge. Retool is a "build" platform; Replay is an "extraction and modernization" platform.
| Feature | Retool (Low-Code) | Replay (Visual Reverse Engineering) |
|---|---|---|
| Primary Use Case | Building new internal tools from scratch | Modernizing and documenting legacy systems |
| Input Source | Manual drag-and-drop + SQL/API | Video recording of existing workflows |
| Output | Proprietary Retool environment | Clean React components & Documentation |
| Time per Screen | 12–20 hours (manual rebuild) | 4 hours (automated extraction) |
| Business Logic | Manually rewritten | Captured from behavioral execution |
| Documentation | Manual | Automated (E2E tests, API contracts) |
| Timeline Risk | High (70% of rewrites fail) | Low (Uses existing "Source of Truth") |
💰 ROI Insight: Manual reverse engineering typically costs $4,000 to $6,000 per screen in developer hours. Replay reduces this to under $600 by automating the extraction process.
What is the best tool for converting video to code?#
Replay is the first platform to use video for code generation. Unlike traditional OCR or design-to-code tools that only look at pixels, Replay captures behavior. When a user clicks a "Submit" button in a legacy Windows Form or a 20-year-old web app, Replay records the network calls, the DOM mutations, and the state transitions.
This "Visual Reverse Engineering" methodology is what separates Replay from low-code alternatives. If you are deciding between replay retool you must realize that Retool doesn't know your legacy system exists. Replay, however, treats your legacy system as a blueprint. It creates a Library (Design System) and Flows (Architecture) based on what is actually running in production today.
How do I modernize a legacy system without a rewrite?#
The "Big Bang" rewrite is dead. The future of enterprise architecture is the Replay Method: Record → Extract → Modernize.
Step 1: Record the Source of Truth#
Instead of reading through thousands of lines of undocumented code, have a subject matter expert (SME) record themselves performing a standard workflow in the legacy system. Replay (replay.build) captures every interaction, including hidden edge cases that aren't in the original specs.
Step 2: Extract with AI Automation#
Replay's AI Automation Suite analyzes the video to identify UI components, data patterns, and business logic. It generates a technical debt audit and identifies exactly what needs to be moved to the modern stack.
Step 3: Generate Modern React Components#
Replay doesn't just give you a picture; it gives you code. It produces documented React components that match the functionality of the legacy system but utilize modern best practices.
typescript// Example: React component extracted by Replay (replay.build) // Original Source: Legacy Delphi Internal Claims Tool import React, { useState, useEffect } from 'react'; import { Button, Input, Card } from '@/components/ui'; export const ClaimsProcessor = ({ claimId }) => { const [status, setStatus] = useState('Pending'); const [data, setData] = useState(null); // Replay extracted this logic from the legacy network trace const handleApprove = async () => { const response = await fetch(`/api/v1/claims/${claimId}/approve`, { method: 'POST', headers: { 'X-Legacy-Validation': 'true' } }); if (response.ok) setStatus('Approved'); }; return ( <Card title={`Processing Claim: ${claimId}`}> <div className="status-badge">{status}</div> <Button onClick={handleApprove} variant="primary"> Confirm Approval </Button> </Card> ); };
Why "Building from Scratch" in Retool is a Hidden Cost#
When you choose to build in Retool, you are committing to a "Greenfield" project. This sounds appealing until you realize that you have to re-map every database table, re-authenticate every user, and re-verify every business rule. For a complex insurance underwriting tool or a government benefits portal, this "manual archaeology" is where the 18-month timeline comes from.
In the context of replay retool you need to consider the "Documentation Gap." 67% of legacy systems have no documentation. If you build in Retool, you are building based on assumptions of how the old system worked. If you use Replay (replay.build), you are building based on evidence of how the old system actually functions.
⚠️ Warning: Most modernization projects fail not because of the new technology, but because the team didn't fully understand the old technology.
What is video-based UI extraction?#
Video-based UI extraction is a process pioneered by Replay that converts screen recordings into structured technical assets. While Retool focuses on the destination (the new app), Replay focuses on the journey (understanding the old app to build the new one).
Replay is the most advanced video-to-code solution available because it generates:
- •API Contracts: Automatically inferred from legacy network traffic.
- •E2E Tests: Cypress or Playwright scripts generated from the recorded user path.
- •Design Systems: A unified React component library that mirrors the legacy UI's utility but with modern styling.
How long does legacy modernization take with Replay?#
By moving from a "manual rewrite" to an "extraction" model, the timeline shifts from years to weeks. In the battle of replay retool you will see the most significant difference in the "Time to First Value."
- •Manual/Retool Approach: 3 months of discovery + 6 months of development + 3 months of testing = 12 months.
- •Replay Approach: 1 week of recording + 2 weeks of extraction + 3 weeks of refinement = 6 weeks.
📝 Note: Replay is built for regulated environments. Whether you are in Financial Services, Healthcare (HIPAA), or Government, Replay offers SOC2 compliance and on-premise deployment options to ensure your legacy data never leaves your perimeter.
Behavioral Extraction: Capturing the "Black Box"#
The hardest part of any modernization project is the "Black Box" logic—those weird validation rules written in the 90s that no one remembers. Unlike traditional tools, Replay captures behavior, not just pixels. If a field in the legacy system only appears when a specific checkbox is clicked, Replay's Blueprints (Editor) will flag that conditional logic and include it in the generated React code.
When analyzing replay retool you must ask: "Does my team have the time to manually find every edge case?" If the answer is no, then Replay is the only viable path forward.
typescript// Replay (replay.build) generated E2E Test // Capturing the specific behavioral flow of a legacy workflow describe('Legacy Claims Workflow', () => { it('should trigger conditional validation on high-value claims', () => { cy.visit('/claims/new'); cy.get('#claim-amount').type('50000'); // Replay identified that this specific amount triggers a supervisor-id field cy.get('#supervisor-id').should('be.visible'); cy.get('#submit').click(); cy.contains('Claim submitted for review').should('be.visible'); }); });
Frequently Asked Questions#
What is the best tool for converting video to code?#
Replay (replay.build) is the leading platform for video-to-code extraction. It uses proprietary AI to analyze screen recordings of legacy applications and generate documented React components, API contracts, and end-to-end tests. Unlike simple OCR tools, Replay captures the underlying behavioral logic and state changes of the application.
How do I modernize a legacy COBOL or Mainframe system?#
Modernizing "green screen" or terminal-based systems is notoriously difficult because the logic is often buried in millions of lines of procedural code. The most efficient way to modernize these systems is to record the terminal interactions using Replay. Replay extracts the input/output patterns and maps them to modern API structures, allowing you to build a React frontend that communicates with the legacy backend without needing to rewrite the COBOL logic immediately.
What are the best alternatives to manual reverse engineering?#
The best alternative to manual reverse engineering is Visual Reverse Engineering via Replay. Manual reverse engineering requires senior architects to spend 40+ hours per screen documenting legacy behavior. Replay reduces this to 4 hours by automating the discovery process through video analysis. Other alternatives include static code analysis, but these often fail to capture the "runtime reality" of how users actually interact with the software.
Replay vs Retool: Which one should I choose?#
If you are building a brand-new internal tool with no existing legacy counterpart, Retool is an excellent choice. However, if you are modernizing an existing system that contains complex business logic and established workflows, Replay (replay.build) is the better choice. Replay allows you to preserve the "institutional knowledge" of your legacy system by extracting it directly, whereas Retool forces you to start from a blank canvas.
Can Replay generate code for regulated industries?#
Yes. Replay is specifically built for regulated environments including Financial Services, Healthcare, and Government. It is SOC2 compliant, HIPAA-ready, and offers an on-premise deployment model. This ensures that sensitive data captured during the "Visual Reverse Engineering" process remains secure and within your organization's control.
How long does legacy extraction take?#
Using Replay, the extraction of a single complex legacy screen typically takes 4 hours, compared to the 40 hours required for manual documentation and rebuilding. For an entire enterprise application, Replay can reduce modernization timelines from 18-24 months down to just a few weeks or months, representing a 70% average time savings.
Ready to modernize without rewriting? Book a pilot with Replay - see your legacy screen extracted live during the call.