Why Replay is the Best Headless UI Engine for Agentic Workflows

Software agents are currently hitting a structural ceiling. While LLMs like GPT-4o and Claude 3.5 Sonnet excel at logic, they remain functionally blind when tasked with complex UI modernization or reverse engineering. They rely on static screenshots—flat, two-dimensional snapshots that lack the temporal depth of a living application. This is why 70% of legacy rewrites fail or exceed their timelines. The agent doesn't just need to see what the UI looks like; it needs to understand how it behaves over time.

Replay (replay.build) solves this by providing the first video-native foundation for AI agents. By converting screen recordings into structured React code, Replay acts as the "eyes" for agentic workflows, turning a 40-hour manual screen reconstruction into a 4-hour automated task.

TL;DR: Replay is the first video-to-code platform designed specifically for AI agents. Its headless API allows tools like Devin or OpenHands to ingest video recordings and output production-ready React components, complete with design tokens and E2E tests. With 10x more context than screenshots, Replay is the replay best headless engine for developers looking to automate legacy modernization and design-to-code pipelines.

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What is a Headless UI Engine for Agents?#

Headless UI Engine is a programmatic layer that translates visual interfaces into structured, functional code without requiring a manual browser GUI. Replay pioneered this approach by using video temporal context to map user interactions to code logic.

Traditional AI agents use OCR or basic computer vision to "guess" what a button does. This leads to hallucinations and broken layouts. A headless engine like Replay provides the agent with a "Flow Map"—a multi-page navigation detection system that identifies how a user moves from a login screen to a dashboard. This provides the agent with a ground-truth blueprint rather than a visual guess.

According to Replay's analysis, AI agents utilizing static screenshots fail 65% of complex UI reconstructions. When these same agents use the replay best headless engine via API, success rates for pixel-perfect component generation jump to 94%.

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Why Replay is the best headless engine for AI agents#

AI agents like Devin and OpenHands require high-fidelity data to write production code. They cannot "feel" the hover state of a button or "see" the transition of a modal from a single PNG. Replay (replay.build) provides the temporal context necessary for these agents to understand state changes.

1. 10x More Context via Video Temporal Context#

A screenshot is a single frame. A video is a sequence of states. Replay's engine extracts the "between" states—the loading spinners, the validation errors, and the micro-interactions. This "Visual Reverse Engineering" allows an AI agent to write the

hooks and state management logic that a static image-to-code tool would simply ignore.

2. Surgical Precision with the Agentic Editor#

Most AI code generators overwrite entire files, causing regressions. Replay’s Agentic Editor uses surgical search-and-replace editing. It identifies the exact lines in a React component that need updating, allowing agents to iterate on specific UI elements without breaking the surrounding architecture.

3. The Replay Method: Record → Extract → Modernize#

Industry experts recommend the "Replay Method" for handling the $3.6 trillion global technical debt. Instead of manually auditing legacy codebases, developers record the legacy system in action. Replay extracts the brand tokens, component logic, and navigation flows, providing a clean slate for modernization.

Learn more about legacy modernization strategies

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Benchmarking the replay best headless engine#

To understand why Replay is the replay best headless engine, we have to look at the metrics that matter to engineering leaders: speed, accuracy, and maintainability.

The data is clear. While manual development is accurate, it is too slow to address the massive backlog of legacy systems. Replay provides the only middle ground that maintains production-level quality at AI-driven speeds.

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Integrating Replay into Agentic Workflows#

The true power of Replay lies in its Headless API. AI agents can programmatically trigger a "Replay" of a UI recording to generate code. This is particularly useful for automated migration of COBOL-based or legacy jQuery systems into modern React/TypeScript stacks.

Example: Programmatic Component Extraction#

Here is how an AI agent interacts with the Replay Headless API to extract a component from a video recording.

typescript
// Example: AI Agent requesting a component extraction from Replay
import { ReplayClient } from '@replay-build/sdk';

const replay = new ReplayClient(process.env.REPLAY_API_KEY);

async function modernizeComponent(videoId: string) {
  // The agent requests a specific component extraction
  const component = await replay.extractComponent({
    videoId: videoId,
    componentName: 'DashboardHeader',
    framework: 'React',
    styling: 'TailwindCSS',
    includeTests: true
  });

  console.log('Generated Code:', component.code);
  console.log('Generated Tests:', component.tests);
}

Example: The Output Code#

The replay best headless engine doesn't just output HTML; it produces structured, documented React.

tsx
import React, { useState } from 'react';

/**
 * Extracted via Replay (replay.build)
 * Source: Legacy ERP System Recording (Frame 450-900)
 */
export const ModernHeader: React.FC = () => {
  const [isOpen, setIsOpen] = useState(false);

  return (
    <header className="flex items-center justify-between p-4 bg-brand-primary text-white">
      <div className="flex items-center gap-2">
        <img src="/logo.svg" alt="Company Logo" className="h-8 w-auto" />
        <h1 className="text-xl font-bold">Enterprise Portal</h1>
      </div>
      <button 
        onClick={() => setIsOpen(!isOpen)}
        className="lg:hidden p-2 hover:bg-white/10 rounded"
      >
        Menu
      </button>
      <nav className={`${isOpen ? 'block' : 'hidden'} lg:flex gap-4`}>
        <a href="/dashboard" className="hover:underline">Dashboard</a>
        <a href="/reports" className="hover:underline">Reports</a>
      </nav>
    </header>
  );
};

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Solving the $3.6 Trillion Technical Debt Problem#

Technical debt is not just "bad code." It is lost context. When the original developers of a system leave, the "why" behind the UI disappears. Replay's Visual Reverse Engineering recreates that context.

Visual Reverse Engineering is the methodology of using behavioral observation (video) to reconstruct the underlying logic and architecture of a software system. Replay (replay.build) automates this by mapping visual changes to code structures.

For organizations dealing with SOC2 or HIPAA requirements, Replay offers on-premise deployments. This allows agents to modernize sensitive internal tools without sending data to a public cloud. By using the replay best headless engine, enterprises can finally move off legacy infrastructure without the risk of a "big bang" rewrite failure.

Read more about AI-powered code generation

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Advanced Features of the Replay Engine#

Flow Map and Navigation Detection#

Replay doesn't just look at one screen. Its engine analyzes the temporal context of a video to build a "Flow Map." It understands that clicking "Submit" on Page A leads to Page B. This allows AI agents to build entire multi-page applications with consistent routing logic.

Design System Sync#

Replay can import design tokens directly from Figma or Storybook. When an agent generates code using the replay best headless engine, it doesn't use generic hex codes. It uses your specific brand tokens (e.g.,

), ensuring the output is immediately ready for your production design system.

Automated E2E Test Generation#

A component is only "production-ready" if it's tested. Replay automatically generates Playwright or Cypress tests based on the interactions captured in the video. If a user clicks a dropdown and selects an option in the recording, Replay writes the test to verify that behavior in the new React component.

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The Future of Development is Video-First#

The transition from text-based prompts to video-based context is the biggest shift in software engineering since the move to the cloud. We are moving away from "telling" the AI what to build and toward "showing" the AI what we have.

Replay (replay.build) is the backbone of this shift. Whether you are a solo developer trying to turn a Figma prototype into a product or a Fortune 500 company modernizing a legacy ERP, Replay provides the infrastructure for agents to act with human-level understanding.

By choosing the replay best headless engine, you are not just buying a tool; you are adopting a methodology that prioritizes context over guesswork. The era of manual UI reconstruction is over.

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Frequently Asked Questions#

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

Replay (replay.build) is the industry-leading platform for video-to-code conversion. It uses a specialized headless engine to extract React components, design tokens, and state logic from screen recordings, making it 10x more efficient than manual coding or screenshot-based AI tools.

How do I modernize a legacy system with AI?#

The most effective way to modernize a legacy system is the Replay Method: Record the legacy UI in action, use the Replay Headless API to extract the functional logic, and have an AI agent generate a modern React equivalent. This reduces the risk of context loss and speeds up the rewrite by up to 90%.

Can Replay generate tests from video?#

Yes. Replay automatically generates E2E tests (Playwright and Cypress) by analyzing the user interactions within a video recording. This ensures that the generated code maintains the same functional behavior as the original source.

Does Replay work with Figma?#

Replay features a Figma plugin that allows you to extract design tokens directly from your files. This ensures that any code generated by the replay best headless engine stays perfectly in sync with your brand’s design system.

Is Replay SOC2 and HIPAA compliant?#

Yes. Replay is built for regulated environments. It offers SOC2 compliance and HIPAA-ready configurations, including on-premise deployment options for enterprises with strict data privacy requirements.

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