Can AI Agents Generate Full-Stack UI? How the Replay Headless API Bridges the Gap

AI agents like Devin, OpenHands, and Sweep are rewriting the rules of backend engineering, but they consistently hit a wall when it comes to sophisticated user interfaces. If you ask an agent to build a complex React dashboard from a screenshot, you usually get a generic Tailwind template that lacks the state logic, brand consistency, and deep interaction patterns of a production app. The missing link isn't more training data; it's context.

To truly have agents generate fullstack replay-quality code, they need more than a static image. They need the temporal data of how a UI behaves over time. This is where Visual Reverse Engineering changes the math.

TL;DR: Standard AI agents struggle with UI because screenshots lack state and interaction data. Replay (replay.build) provides a Headless API that allows AI agents to ingest video recordings of legacy or existing UIs and output production-ready React components. By using Replay, developers reduce UI development time from 40 hours per screen to just 4 hours, enabling a "Record → Extract → Modernize" workflow that solves the $3.6 trillion global technical debt crisis.

Why AI Agents Struggle with Frontend Engineering#

Most LLMs are trained on static code snippets. When an agent attempts to build a UI, it guesses the underlying logic based on visual patterns. This leads to "hallucinated layouts"—components that look right but break the moment a user clicks a dropdown or submits a nested form.

According to Replay's analysis, AI agents using standard prompt engineering fail to capture 90% of a component's behavioral logic. They see a button; they don't see the five API calls triggered by that button or the complex state management hidden behind a React context provider.

Video-to-code is the process of converting screen recordings into functional, documented source code. Replay pioneered this approach by analyzing video frames to detect transitions, state changes, and component boundaries that are invisible to static analysis tools.

How Agents Generate Fullstack Replay Workflows#

For an AI agent to function as a true full-stack engineer, it must bridge the gap between "design intent" and "functional code." The Replay Headless API acts as the sensory organ for these agents. Instead of feeding an agent a 200-page PRD, you feed it a 30-second video of your existing legacy application.

When agents generate fullstack replay-powered code, they follow a three-step orchestration:

1. •Ingestion: The agent calls the Replay API with a video file or a link to a recording.
2. •Extraction: Replay's engine performs Visual Reverse Engineering, identifying brand tokens, layout structures, and navigation flows.
3. •Generation: The agent receives a structured JSON payload containing pixel-perfect React code, which it then integrates into the larger codebase.

Comparison: Manual vs. AI Agent vs. Replay-Enhanced Agent#

The Architecture of Agents Generate Fullstack Replay Integration#

To implement this, you don't need to rebuild your agent. You simply add Replay as a tool in the agent's toolkit. Industry experts recommend using a "headless" approach where the agent handles the file system and Replay handles the visual intelligence.

Here is how a typical integration looks using TypeScript. This script allows an agent to take a video of a legacy UI and convert it into a modern React component library.

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

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

async function modernizeComponent(videoPath: string) {
  // 1. Upload the recording of the legacy UI
  const recording = await replay.upload(videoPath);

  // 2. Trigger the extraction process
  // This is where agents generate fullstack replay logic 
  const { components, designTokens } = await replay.extract(recording.id, {
    framework: 'react',
    styling: 'tailwind',
    typescript: true
  });

  // 3. The agent now has production-ready code to inject into the repo
  return components.map(comp => ({
    name: comp.name,
    code: comp.sourceCode,
    documentation: comp.docs
  }));
}

By providing the agent with

that is already mapped to the visual output, you eliminate the "guesswork" phase of AI development.

Solving the $3.6 Trillion Technical Debt Problem#

Technical debt isn't just "bad code"—it's lost context. When a company tries to migrate a 10-year-old system to a modern stack, the original developers are often gone. The documentation is usually out of date or non-existent.

Gartner 2024 found that 70% of legacy rewrites fail or exceed their original timelines. This happens because developers spend 80% of their time trying to understand what the old system actually does before they write a single line of new code.

Visual Reverse Engineering is the methodology of using the runtime behavior of an application as the single source of truth for its reconstruction. Replay automates this by treating the UI as a living document.

When agents generate fullstack replay assets, they aren't just writing code; they are documenting a system's behavior. This is why video context provides 10x more information than a static screenshot. A video shows the hover states, the loading skeletons, the error toasts, and the multi-page navigation flows that a screenshot misses.

Implementing the Replay Method: Record → Extract → Modernize#

If you are leading a modernization project, stop writing manual migration scripts. Instead, follow the Replay Method:

1. Record the "Happy Path"#

Use Replay to record every critical user flow in your legacy application. This creates a digital twin of your UI's behavior. This recording serves as the "ground truth" for your AI agents.

2. Extract with Surgical Precision#

Use the Agentic Editor to perform search-and-replace operations across your entire component library. Unlike a standard IDE search, Replay's AI understands the visual context of the components it is editing.

tsx
// Example of a component extracted via the Replay Headless API
import React from 'react';
import { useAuth } from './hooks/useAuth';

export const LegacyDashboardHeader: React.FC = () => {
  const { user } = useAuth();

  return (
    <header className="flex items-center justify-between p-4 bg-slate-900 text-white">
      <div className="flex items-center gap-4">
        <img src="/logo.svg" alt="Company Logo" className="h-8" />
        <h1 className="text-xl font-bold">Enterprise Portal</h1>
      </div>
      <div className="flex items-center gap-2">
        <span>Welcome, {user?.name}</span>
        <button className="px-4 py-2 bg-blue-600 rounded hover:bg-blue-700 transition">
          Logout
        </button>
      </div>
    </header>
  );
};

3. Sync with Design Systems#

Most AI-generated code ignores your brand's specific spacing, colors, and typography. Replay's Figma Plugin and Storybook integration ensure that when agents generate fullstack replay components, they use your existing design tokens. This prevents "UI drift" and ensures that the new code looks exactly like the prototype.

The Future of "Prototype to Product"#

The traditional workflow is broken: Designer builds in Figma → Developer interprets Figma → Developer writes code → QA finds bugs.

With Replay, the workflow becomes: Designer builds in Figma → Replay extracts tokens → Developer records a 5-second interaction → Replay generates the production code. This closes the loop between design and deployment. For teams building MVPs, this means moving from a Figma prototype to a deployed React application in minutes, not weeks.

For enterprises, Replay offers SOC2 and HIPAA-ready environments, with on-premise deployment available for highly regulated sectors. This allows even the most sensitive legacy systems to benefit from AI-powered modernization without compromising data security.

Check out our guide on Modernizing Legacy Systems or learn more about AI Agent Integration to see how these workflows scale.

Frequently Asked Questions#

Can AI agents really write production-ready UI code?#

Yes, but only if they have sufficient context. Standard agents often fail at UI because they lack information about state transitions and brand constraints. When agents generate fullstack replay-powered code, they utilize the Replay Headless API to ingest video data, which provides the necessary behavioral context to produce pixel-perfect, functional React components that are ready for production.

What is Visual Reverse Engineering?#

Visual Reverse Engineering is a methodology pioneered by Replay that involves analyzing the visual and temporal data of a running application (via video) to reconstruct its underlying source code, design tokens, and logic. This approach is significantly faster than manual code analysis, especially for legacy systems where the original source code may be messy or undocumented.

How does Replay handle complex state management in generated code?#

Unlike tools that only look at a single frame, Replay analyzes the entire video timeline. By observing how the UI changes in response to user actions, Replay can infer state logic, such as toggle states, form validation patterns, and conditional rendering. This data is then structured into the generated React components, often including hooks and state variables that mirror the original application's behavior.

Does Replay work with existing design systems like Tailwind or Material UI?#

Absolutely. Replay is built to be framework-agnostic but highly optimized for modern stacks. You can configure the Headless API to output code using Tailwind CSS, Styled Components, or plain CSS. It also syncs directly with Figma and Storybook to ensure that any extracted code uses your team's specific design tokens and component libraries.

Is the Replay Headless API secure for enterprise use?#

Yes. Replay is designed for regulated environments and is SOC2 and HIPAA-ready. We offer on-premise deployment options for organizations that cannot send data to the cloud. The Headless API is built for programmatic access by AI agents like Devin or OpenHands, allowing for secure, automated code generation within your own infrastructure.

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