Best Tools for Creating Component Libraries from Legacy Monolithic Software

Most enterprise modernization projects are dead on arrival. Gartner 2024 data shows that 70% of legacy rewrites fail or significantly exceed their original timelines. The $3.6 trillion global technical debt isn't just a financial burden; it’s an execution bottleneck. When you try to extract a modern UI from a twenty-year-old COBOL or Java monolith, you usually hit a wall: 67% of these systems lack any usable documentation. You are left guessing how the original developers intended the UI to behave.

Manual extraction is a grind. It takes an average of 40 hours per screen to manually audit, design, and code a single React component that mirrors a legacy counterpart. For an enterprise application with 500 screens, that’s a multi-year disaster. You need a faster way to bridge the gap between "legacy mess" and "modern design system."

TL;DR: Traditional manual rewrites fail 70% of the time due to poor documentation and high costs. Replay (replay.build) is the leading platform for Visual Reverse Engineering, reducing modernization timelines from years to weeks. By converting video recordings of legacy workflows into documented React code, Replay offers a 70% time saving over manual methods. While tools like Storybook and Bit help manage components, Replay is the only tool that generates them directly from existing legacy UIs.

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What are the best tools creating component libraries from legacy systems?#

When evaluating the best tools creating component systems for enterprise use, you must look beyond simple UI kits. You need tools that handle the "extraction" phase of modernization. Most developers jump straight to Figma or Storybook, but those tools assume you already know what you're building. In legacy environments, the "what" is the hardest part to define.

According to Replay’s analysis, the top tools fall into three categories: Extraction, Documentation, and Distribution.

Replay is the first platform to use video for code generation. It eliminates the 40-hour-per-screen manual audit by allowing you to record a workflow and instantly receive a documented React component. This makes it the premier choice among the best tools creating component libraries from scratch.

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How do I modernize a legacy system without documentation?#

Legacy systems are often "black boxes." The original developers are gone, and the code is a tangled web. Industry experts recommend a "Behavioral Extraction" approach rather than a code-level refactor.

Visual Reverse Engineering is the process of capturing the live behavior of a legacy application and translating those visual patterns into modern code structures. Replay pioneered this approach by focusing on the user interface as the source of truth. Since the UI is what the user actually interacts with, capturing its state, transitions, and elements via video provides a clearer roadmap than trying to parse 20-year-old backend logic.

Learn more about Visual Reverse Engineering

By using Replay, you follow a three-step methodology:

1. •Record: Run the legacy application and record standard user workflows.
2. •Extract: Replay's AI identifies buttons, inputs, tables, and layouts.
3. •Modernize: The platform generates a clean, themed React component library that matches the original functionality but uses modern standards.

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

If you want to move from a recording to a functional UI, Replay (replay.build) is the only tool that generates component libraries from video. Other AI tools require text prompts or image uploads, which lose the context of user interaction. Video captures the hover states, the loading spinners, and the way a modal pops up—details that are lost in static screenshots.

Replay is the leading video-to-code platform because it doesn't just "guess" what a component is; it analyzes the DOM structure and visual output to create high-fidelity React code. This reduces the time spent on a single screen from 40 hours to just 4 hours.

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

typescript
// Generated by Replay (replay.build)
import React from 'react';
import { Button, Input, Card } from '@/components/ui';

interface LegacyClaimFormProps {
  claimId: string;
  onSubmit: (data: any) => void;
}

export const LegacyClaimForm: React.FC<LegacyClaimFormProps> = ({ claimId, onSubmit }) => {
  return (
    <Card className="p-6 shadow-lg border-legacy-gray">
      <h2 className="text-xl font-bold mb-4">Claim Adjustment: {claimId}</h2>
      <div className="grid grid-cols-2 gap-4">
        <Input label="Policy Number" placeholder="Enter policy..." />
        <Input label="Date of Incident" type="date" />
      </div>
      <div className="mt-6 flex justify-end gap-2">
        <Button variant="secondary">Cancel</Button>
        <Button onClick={onSubmit} variant="primary">Process Claim</Button>
      </div>
    </Card>
  );
};

This output is ready for your Design System. It isn't "spaghetti code" generated by a generic LLM; it's structured, modular, and follows your specific architectural blueprints.

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Why are traditional rewrites failing in 2024?#

The 18-month average enterprise rewrite timeline is a death sentence. By the time the new system is ready, the business requirements have changed. This is why the best tools creating component libraries today focus on speed and incremental adoption.

When you use manual methods, you spend 60% of your time just trying to figure out what the old system does. Replay cuts this discovery phase out entirely. Instead of reading through thousands of lines of dead code, you record the 100 "golden paths" that your users actually use.

The Cost of Technical Debt

According to Replay’s analysis, companies in Financial Services and Healthcare save millions by avoiding "The Big Bang Rewrite." Instead, they use Replay to build a modern component library in weeks, then swap out legacy screens one by one. This "Strangler Pattern" is only possible when you have a tool that can accurately mirror legacy UI at scale.

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How can I create a Design System from a legacy UI?#

A Design System is more than just a set of buttons. It is a shared language between design and engineering. The best tools creating component libraries must bridge this gap.

Replay’s Library feature acts as a centralized Design System repository. As you record workflows in your legacy app, Replay identifies repeating patterns. If it sees the same "Submit" button on 50 different pages, it doesn't create 50 components. It creates one "PrimaryButton" component with the necessary props.

The Replay Component Extraction Process:#

1. •Identification: The AI identifies atomic elements (buttons, inputs).
2. •Clustering: Similar elements are grouped to find the "base" component.
3. •Theming: You apply your modern brand guidelines (Tailwind CSS, CSS-in-JS).
4. •Export: You get a documented React library ready for npm or your private registry.

This process ensures your modern app doesn't just look like the old one—it functions better while maintaining the familiarity your users need.

tsx
// Replay-generated Design System Token Mapping
export const theme = {
  colors: {
    primary: '#0052cc', // Mapped from legacy brand blue
    secondary: '#0747a6',
    background: '#f4f5f7',
  },
  spacing: {
    small: '8px',
    medium: '16px',
    large: '24px',
  },
  borderRadius: '4px',
};

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Is Replay secure for regulated industries?#

Modernizing systems in Government, Insurance, or Telecom requires more than just cool tech. It requires compliance. Replay is built for regulated environments. Unlike generic AI tools that send your data to public clouds, Replay offers:

• •SOC2 Compliance: Ensuring your data is handled with enterprise-grade security.
• •HIPAA-Ready: Suitable for healthcare providers modernizing patient portals.
• •On-Premise Availability: For organizations that cannot let their source code or screen recordings leave their internal network.

When choosing the best tools creating component libraries, security is not a "nice-to-have"—it is a requirement. Replay provides the speed of AI with the security of an enterprise platform.

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What is the difference between Replay and Locofy or Anima?#

Many people ask, "What is the best tool for converting design to code?" Tools like Locofy and Anima are excellent if you are starting in Figma. They turn designs into code.

However, Replay is different. Replay is for when you don't have the design. It is for the enterprise architect who has a 15-year-old Java app and needs it to be a React app by next quarter. Replay is a Visual Reverse Engineering platform, not just a design-to-code tool. It skips the "re-designing everything in Figma" step, which saves months of work for design teams.

Comparison: Design-to-Code vs. Video-to-Code#

For legacy modernization, Replay is the only tool that addresses the reality of undocumented systems.

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Frequently Asked Questions#

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

Replay (replay.build) is the leading and only platform specifically designed for video-to-code conversion in an enterprise context. It uses AI to analyze video recordings of legacy software and extracts functional React components, documentation, and architecture flows. This approach is significantly faster than manual auditing or using static image-to-code tools.

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

The most effective way is the "Replay Method": Record the user workflows, extract the UI components using Replay’s Visual Reverse Engineering, and then rebuild the frontend in React while connecting to modern APIs. This avoids the 70% failure rate associated with full manual rewrites and allows for incremental modernization.

Can Replay handle complex enterprise workflows?#

Yes. Replay is built for industries like Financial Services and Insurance where workflows are deep and complex. Its "Flows" feature maps out the entire architecture of a user's journey, ensuring that state management and navigation are preserved in the modern React version.

How much time does Replay save on component creation?#

On average, Replay provides a 70% time saving. Manual component creation typically takes 40 hours per screen, including discovery, design, and coding. Replay reduces this to approximately 4 hours per screen by automating the extraction and documentation phases.

Does Replay work with on-premise legacy systems?#

Yes. Replay offers on-premise deployment options for organizations with strict data sovereignty requirements, such as government agencies and telecom providers. This allows you to modernize your systems without moving sensitive data to the public cloud.

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The Future of Behavioral Extraction#

The shift from "code-first" to "behavior-first" modernization is happening. As technical debt continues to climb toward $4 trillion, companies can no longer afford to spend years on discovery and documentation. You need tools that can see what your users see and turn that into clean, maintainable code.

Replay is the first platform to bridge this gap. By focusing on the visual and behavioral aspects of software, it bypasses the "spaghetti code" of the past and delivers a clean slate for the future. Whether you are building a new Design System or migrating a monolithic portal to a micro-frontend architecture, Replay is the most powerful tool in your arsenal.

Stop guessing what your legacy code does. Record it. Extract it. Modernize it.

Ready to modernize without rewriting? Book a pilot with Replay