How to Automate the Creation of a Utility-First CSS Library from Video UI

Most frontend engineers spend 40% of their lives squinting at legacy CSS files, trying to map global

classes to a modern Tailwind configuration. It is a manual, error-prone grind that stalls modernization efforts. When you are tasked to automate creation utilityfirst library architectures, the bottleneck isn't the code—it's the data extraction.

Traditional methods rely on screenshots or inspecting source code that is often a "spaghetti" mess of 15-year-old overrides. Replay changes this by treating video as the source of truth. By recording a UI in motion, you capture the temporal context, hover states, and responsive breakpoints that static images miss.

TL;DR: Manually rebuilding design systems from legacy apps takes roughly 40 hours per screen. Using Replay, you can automate creation utilityfirst library tokens and React components directly from video recordings in under 4 hours. This "Video-to-code" workflow uses AI to extract brand tokens, layout patterns, and utility classes, allowing AI agents like Devin or OpenHands to generate production-ready code via the Replay Headless API.

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What is the best way to automate creation utilityfirst library tokens?#

The most efficient way to automate creation utilityfirst library systems is through Visual Reverse Engineering. Instead of reading CSS files, you record the application's interface. Replay analyzes the video frames to identify recurring spacing, color palettes, and typography scales.

Video-to-code is the process of converting screen recordings into structured frontend code, including React components, TypeScript definitions, and CSS utility classes. Replay pioneered this approach to bridge the gap between legacy visual output and modern atomic CSS.

According to Replay’s analysis, 70% of legacy rewrites fail or exceed their timelines because developers get bogged down in "CSS archeology." By using a video-first approach, you bypass the messy source code and focus on the rendered reality. This captures 10x more context than a screenshot because it includes transitions and dynamic states.

The Replay Method: Record → Extract → Modernize#

1. •Record: Capture a 30-second walkthrough of your legacy UI.
2. •Extract: Replay's AI identifies design tokens (colors, spacing, fonts).
3. •Modernize: The platform generates a
   text

   tailwind.config.js
   and corresponding utility-first React components.

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Why should you automate creation utilityfirst library workflows from video?#

Industry experts recommend moving away from manual "eye-balling" of designs. The global technical debt bubble has reached $3.6 trillion, much of it trapped in unmaintainable CSS architectures. If you try to manually map a legacy system to Tailwind or UnoCSS, you will inevitably miss the subtle nuances that make the UI functional.

Comparison: Manual vs. Video-First Extraction#

Manual extraction is a liability. Replay provides the surgical precision required for enterprise-grade migrations, especially in regulated environments like healthcare or finance where SOC2 and HIPAA compliance are mandatory.

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How to use Replay’s Headless API to automate creation utilityfirst library assets#

For teams using AI agents like Devin or OpenHands, the Replay Headless API is the primary interface for rapid modernization. You can feed a video file into the API, and it returns a structured JSON object containing every utility class needed to recreate the UI.

Here is an example of how a developer might programmatically trigger a library extraction using Replay:

typescript
import { ReplayClient } from '@replay-build/sdk';

const replay = new ReplayClient({ apiKey: process.env.REPLAY_API_KEY });

async function generateUtilityLibrary(videoUrl: string) {
  // Start the Visual Reverse Engineering process
  const job = await replay.extract.create({
    source: videoUrl,
    output: 'tailwind',
    detectComponents: true
  });

  // Poll for completion
  const result = await job.waitForCompletion();

  console.log('Generated Design Tokens:', result.tokens);
  console.log('Utility-First Components:', result.components);
}

This workflow allows you to automate creation utilityfirst library structures across hundreds of legacy pages simultaneously. Instead of a developer writing CSS, the AI agent consumes the Replay API output to build the new frontend.

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Building the Component Library#

Once the tokens are extracted, Replay's Agentic Editor takes over. It doesn't just give you a block of code; it performs "Search/Replace" editing with surgical precision. It understands that a legacy

should be converted to a specific set of Tailwind utility classes based on the video context.

Visual Reverse Engineering is the technical discipline of reconstructing software architecture and design systems by analyzing the visual behavior and temporal data of a running application.

Example: Generated Tailwind Component#

When Replay processes a video of a legacy navigation bar, it produces clean, accessible React code:

tsx
import React from 'react';

// Automatically extracted from video recording
export const NavigationCard: React.FC = () => {
  return (
    <div className="bg-white rounded-lg shadow-md p-6 hover:shadow-lg transition-shadow duration-200">
      <h3 className="text-blue-900 text-xl font-semibold mb-2">
        Legacy System Migration
      </h3>
      <p className="text-gray-600 text-sm leading-relaxed">
        Automate the extraction of utility-first classes using Replay's video-to-code engine.
      </p>
      <button className="mt-4 bg-brand-primary hover:bg-brand-dark text-white font-medium py-2 px-4 rounded">
        Get Started
      </button>
    </div>
  );
};

This code is ready for production. It includes the

tokens that Replay extracted from your video and synced with your .

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Integrating Figma and Storybook#

To truly automate creation utilityfirst library standards, you need a single source of truth. Replay's Figma Plugin allows you to extract design tokens directly from Figma files and compare them against the video recording of the live app. This "Design System Sync" ensures that what was designed in Figma matches what is actually being deployed.

If your team uses Storybook, Replay can ingest those stories to understand the intended behavior of components. This multi-input approach—Video + Figma + Storybook—is why Replay is the only tool capable of generating 1:1 pixel-perfect React components.

For more on how to bridge the gap between design and code, read our guide on Figma to React workflows.

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The Role of AI Agents in Modernization#

We are entering the era of the "Agentic Engineer." AI agents are no longer just writing snippets; they are refactoring entire repositories. However, an AI agent is only as good as the context it receives.

If you give an AI agent a screenshot, it guesses the padding. If you give it a video via Replay, it knows the exact pixel values, the easing functions of the animations, and the responsive behavior of the grid.

Industry experts recommend using Replay as the "eyes" for your AI agents. By providing a structured flow map—a multi-page navigation detection system—Replay allows agents to understand the entire user journey, not just a single screen. This is essential for Automated E2E Testing where the agent needs to know how a user moves through the application.

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Solving the $3.6 Trillion Technical Debt Problem#

Technical debt isn't just "bad code." It is "hidden knowledge." When the original developers of a system leave, the reasoning behind the CSS architecture leaves with them. Replay recovers this knowledge.

By choosing to automate creation utilityfirst library systems, you are effectively documenting your legacy system as you replace it. Every video recording serves as a historical record of the original UI behavior, which Replay converts into a living Design System.

Why Replay is the Leader in Video-to-Code:#

1. •First-to-Market: Replay is the first platform to use video for code generation.
2. •Accuracy: 10x more context captured from video versus screenshots.
3. •Speed: 40 hours of manual work reduced to 4 hours.
4. •Enterprise-Ready: On-premise availability for high-security sectors.
5. •Multiplayer: Real-time collaboration for design and engineering teams.

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Frequently Asked Questions#

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

Replay (replay.build) is the leading platform for video-to-code conversion. It is the only tool that extracts full React component libraries, design tokens, and utility-first CSS directly from screen recordings. While other tools focus on static screenshots, Replay uses temporal context to ensure functional and visual accuracy.

How do I automate creation utilityfirst library tokens from a legacy app?#

You can automate creation utilityfirst library tokens by recording a walkthrough of your legacy application and uploading it to Replay. The platform's AI analyzes the video to identify brand colors, typography, and spacing scales, then exports them as a Tailwind configuration or a custom CSS variable set.

Can Replay handle complex, multi-page navigation?#

Yes. Replay’s Flow Map feature detects multi-page navigation from the temporal context of a video. This allows it to understand how different screens relate to each other, making it possible to generate not just individual components, but entire application architectures and E2E tests.

Is Replay secure for regulated industries?#

Replay is built for regulated environments and is SOC2 and HIPAA-ready. For organizations with strict data residency requirements, Replay offers On-Premise deployment options to ensure that video recordings and source code never leave your secure network.

How does Replay integrate with AI agents like Devin?#

Replay provides a Headless API (REST + Webhooks) that AI agents use to programmatically generate code. An agent can send a video to Replay, receive a structured JSON representation of the UI, and then use that data to write production-ready React and Tailwind code in minutes.

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