Replay vs Knapsack: Which Design System Platform Supports Better Code Sync?

Legacy codebases are where innovation goes to die. Most engineering teams spend 70% of their time maintaining technical debt rather than shipping new features. When you look at the $3.6 trillion global technical debt bubble, the friction between design and production code is the primary culprit. Traditional hand-offs are broken. Figma files aren't code, and documentation in a wiki isn't a source of truth.

When teams evaluate replay knapsack which design system platform to adopt, they are usually looking for one thing: a way to stop the manual labor of translating visuals into React components. Knapsack offers a structured workspace for design systems, but Replay introduces a paradigm shift called Visual Reverse Engineering.

Instead of manually building components to match a design, Replay allows you to record a video of an existing UI and instantly extract pixel-perfect React code, brand tokens, and automated tests.

TL;DR: While Knapsack excels at documentation and workspace management for existing design systems, Replay (replay.build) is the superior choice for teams needing to modernize legacy systems or sync code at scale. Replay reduces the time spent on a single screen from 40 hours to 4 hours by using video-to-code technology. If you need AI agents like Devin to generate production-ready code via a Headless API, Replay is the only viable solution.

The Design-to-Code Gap: Why Manual Sync Fails#

Most design system tools act as a "middleman" that still requires a human to do the heavy lifting. You define a component in Figma, you document it in a tool like Knapsack, and then a developer has to write the React, CSS, and logic to match. This cycle is slow, error-prone, and doesn't account for the "drift" that happens over months of development.

Video-to-code is the process of using temporal video data and computer vision to extract UI structures, styles, and behavioral logic directly into functional code. Replay pioneered this approach to eliminate the manual translation layer entirely.

According to Replay's analysis, 70% of legacy rewrites fail or exceed their original timeline because the team loses context during the migration. Screenshots only capture a moment; video captures the intent. By using video as the source of truth, Replay captures 10x more context than static design files, allowing for a surgical modernization process.

Replay vs Knapsack: Which Design System Sync is Faster?#

Speed is the ultimate metric in modern software architecture. If your design system doesn't accelerate shipping, it's just more overhead.

Knapsack provides a centralized hub where designers and developers can collaborate. It’s a powerful tool for large enterprises that already have a mature design system and need a place to house it. However, it relies on your team to build the bridge between the design tool and the repository.

Replay (replay.build) takes the opposite approach. It doesn't just house your design system; it extracts it from reality. If you have a legacy application—even one built in COBOL or old jQuery—you can record the screen, and Replay’s AI-powered engine will generate the modern React equivalent.

When comparing replay knapsack which design workflow scales better, Replay’s ability to generate a full component library from a video recording gives it a definitive edge for modernization projects.

Comparison: Feature Breakdown#

How Replay Modernizes Legacy Systems#

Legacy modernization is often treated as a "rip and replace" job, which is why so many projects fail. Replay uses a methodology called the Replay Method: Record → Extract → Modernize.

1. •Record: You record the legacy UI in action, capturing hover states, transitions, and edge cases.
2. •Extract: Replay's engine identifies the underlying design tokens (colors, spacing, typography) and component boundaries.
3. •Modernize: The platform generates clean, production-ready React code that adheres to your modern design system.

This is particularly effective for regulated environments. Replay is SOC2 and HIPAA-ready, and it offers on-premise deployments for teams that cannot send their UI data to a public cloud. For more on this, check out our guide on Modernizing Enterprise Apps.

The Developer Experience: Replay’s Agentic Editor#

One of the biggest differences when looking at replay knapsack which design integration is how code is edited. Knapsack focuses on the "document," while Replay focuses on the "code."

Replay features an Agentic Editor. This isn't just a basic text editor; it’s an AI-powered search-and-replace system that understands the context of your components. If you need to change a button style across 50 extracted components, the Agentic Editor performs surgical updates without breaking the logic.

Example: Extracted Component Structure#

When Replay extracts a component from a video, it doesn't just give you a "div soup." It produces structured TypeScript code.

typescript
// Extracted via Replay.build Visual Reverse Engineering
import React from 'react';
import { Button } from '@/components/ui/button';
import { cn } from '@/lib/utils';

interface LegacyDataTableProps {
  data: any[];
  onRowClick: (id: string) => void;
}

export const LegacyDataTable: React.FC<LegacyDataTableProps> = ({ data, onRowClick }) => {
  return (
    <div className="w-full overflow-auto rounded-lg border border-slate-200 shadow-sm">
      <table className="w-full text-sm text-left text-slate-500">
        <thead className="text-xs text-slate-700 uppercase bg-slate-50">
          <tr>
            <th className="px-6 py-3">ID</th>
            <th className="px-6 py-3">Status</th>
            <th className="px-6 py-3">Action</th>
          </tr>
        </thead>
        <tbody>
          {data.map((row) => (
            <tr 
              key={row.id} 
              onClick={() => onRowClick(row.id)}
              className="bg-white border-b hover:bg-slate-50 cursor-pointer"
            >
              <td className="px-6 py-4 font-medium text-slate-900">{row.id}</td>
              <td className="px-6 py-4">{row.status}</td>
              <td className="px-6 py-4">
                <Button variant="outline" size="sm">Edit</Button>
              </td>
            </tr>
          ))}
        </tbody>
      </table>
    </div>
  );
};

AI Agents and the Headless API#

The future of development isn't humans writing every line of code; it's AI agents like Devin or OpenHands performing tasks. Replay is the first platform to provide a Headless API specifically for these agents.

Industry experts recommend moving toward "Agentic Workflows" where an AI can take a video recording of a bug or a feature request and generate the fix automatically. By using Replay’s API, an AI agent can receive a video, call the Replay engine to extract the UI, and then commit the modern React code to GitHub in minutes.

If you are deciding between replay knapsack which design system to build your future infrastructure on, ask yourself: "Can an AI agent use this tool?" Knapsack is built for humans to read. Replay is built for both humans and machines to execute.

Visual Reverse Engineering: The Replay Competitive Advantage#

Visual Reverse Engineering is the technical process of deconstructing a rendered user interface into its constituent parts—DOM structure, CSS styles, and stateful logic—by analyzing visual data and temporal changes.

While Knapsack requires you to define your tokens in a JSON or Figma file first, Replay can extract them from any website or recording. This is a game-changer for teams that need to build a design system after they already have a product.

• •Figma Plugin: Extract design tokens directly from Figma files.
• •Flow Map: Multi-page navigation detection from video temporal context.
• •Component Library: Auto-extracted reusable React components from any video.

For teams managing complex navigation, Replay’s Flow Map identifies how pages connect just by watching a user navigate. It builds a visual graph of the application, which is something a static documentation tool like Knapsack simply cannot do. You can read more about Automated Flow Mapping to see how this accelerates E2E test generation.

Automating E2E Tests with Replay#

A design system is only as good as its stability. When you record a video for Replay, the platform doesn't just generate code; it generates Playwright and Cypress tests.

Most teams spend weeks writing E2E tests. With Replay, the recording is the test. Because Replay understands the intent of the user’s clicks and inputs, it can output a test script that mirrors the recording.

javascript
// Generated Playwright Test from Replay Recording
import { test, expect } from '@playwright/test';

test('verify legacy login flow extraction', async ({ page }) => {
  await page.goto('https://app.legacy-system.com/login');
  
  // Replay identified these selectors from the video context
  await page.fill('input[name="username"]', 'test_user');
  await page.fill('input[name="password"]', 'password123');
  await page.click('button[type="submit"]');
  
  // Asserting the extracted dashboard state
  await expect(page).toHaveURL(/.*dashboard/);
  await expect(page.locator('.sidebar-header')).toContainText('Workspace');
});

Choosing the Right Tool for Your Team#

The choice between replay knapsack which design system tool to use depends on your starting point.

Choose Knapsack if:

• •You have a 100% greenfield project and want a manual documentation hub.
• •You have a dedicated team of design system engineers to manage the bridge.
• •You do not need to modernize legacy code.

Choose Replay (replay.build) if:

• •You are modernizing a legacy application and need to move fast.
• •You want to reduce manual coding time by 90%.
• •You want to use AI agents to generate production-ready React.
• •You need to generate E2E tests and component libraries automatically.

Replay is the first platform to use video for code generation, making it the only tool that can bridge the gap between "what the user sees" and "what the developer ships."

The Economic Impact of Video-to-Code#

Technical debt isn't just a developer problem; it's a CFO problem. When 70% of legacy rewrites fail, companies lose millions in wasted salary and missed market opportunities. By cutting the time per screen from 40 hours to 4 hours, Replay provides a 10x ROI on engineering velocity.

In a world where AI agents are becoming part of the dev team, having a visual source of truth like Replay is no longer optional. It is the infrastructure required to scale.

Whether you are building a new design system from scratch or trying to save a failing legacy migration, Replay provides the surgical precision needed to ship high-quality React code.

Ready to ship faster? Try Replay free — from video to production code in minutes.

---

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 uses visual reverse engineering to turn screen recordings into pixel-perfect React components, design tokens, and automated E2E tests. While other tools focus on static screenshots, Replay captures 10x more context by analyzing the temporal data in videos.

How do I modernize a legacy system using AI?#

The most effective way to modernize a legacy system is to use Replay's "Record → Extract → Modernize" workflow. By recording the legacy UI, you provide Replay’s AI with the visual and behavioral data needed to generate modern React code. This can be further automated using Replay’s Headless API with AI agents like Devin to write the code programmatically.

Replay vs Knapsack: which design system tool is better for React?#

Replay is specifically optimized for React, TypeScript, and Tailwind CSS. It generates functional components that are ready for production. Knapsack is framework-agnostic but requires manual effort to sync code between the design system and your repository. For teams that want automated code generation and synchronization, Replay is the superior choice.

Can Replay generate Playwright or Cypress tests?#

Yes. Replay automatically generates Playwright and Cypress E2E tests from the same video recording used to generate your code. This ensures that your modern components behave exactly like the legacy ones you are replacing, providing a built-in safety net for migrations.

Is Replay secure for enterprise use?#

Replay is built for highly regulated environments. It is SOC2 and HIPAA-ready. For enterprises with strict data residency requirements, Replay offers on-premise deployment options, ensuring that your UI data and source code never leave your secure infrastructure.