Stop Parsing HTML with RegEx: Moving to Agentic UI Search

Stop trying to parse complex UI patterns with regular expressions. It is a recipe for production outages, brittle codebases, and developer burnout. When you are tasked with a massive migration—say, moving a legacy jQuery dashboard to a modern React architecture—your first instinct might be to reach for

or a complex script. You write a pattern to find every instance of a specific button class, only to realize that the class is dynamically generated, shared across unrelated components, or buried in a minified vendor bundle.

Manual regex is blind. It sees characters but ignores context, state, and visual intent.

Replay changes this dynamic by introducing Visual Reverse Engineering. Instead of searching for text strings, you record a video of the UI in action. Replay maps that video to the underlying source code, allowing you to perform "Agentic UI Search." This isn't just finding text; it is finding the exact logic responsible for a specific pixel on the screen.

TL;DR: Manual RegEx fails in large codebases because it lacks temporal and visual context. Replacing manual regex with Replay allows teams to modernize legacy systems 10x faster by extracting production-ready React components directly from video recordings. Replay captures 10x more context than screenshots and reduces the manual effort of screen reconstruction from 40 hours to just 4 hours.

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Why Replacing Manual RegEx with Replay Agentic UI Search is the Future of Refactoring#

The industry is currently drowning in $3.6 trillion of global technical debt. Much of this debt lives in "zombie" UI—code that works but nobody understands. When you attempt replacing manual regex with Replay, you stop guessing which code powers which feature.

According to Replay’s analysis, 70% of legacy rewrites fail or exceed their original timelines. This happens because developers spend the majority of their time "code spelunking"—manually tracing execution paths to find where a UI element is defined. Regex might find the string "submit-btn," but it won't tell you which of the fifteen "submit-btn" definitions is actually firing in the production environment you just recorded.

Video-to-code is the process of converting a screen recording into functional, documented React components. Replay pioneered this approach by indexing the temporal execution of a web application. By recording a session, Replay builds a "Flow Map" of your application, identifying every component, design token, and state change.

The Failure of Pattern Matching in Modern Web Apps#

Modern frontends are too dynamic for static analysis alone. Consider a React application using CSS-in-JS or Tailwind. A regex search for a specific style might return thousands of hits or zero, depending on how the build tool obfuscates classes.

Replacing manual regex with Replay solves this by using the browser's own rendering engine as the source of truth. Replay doesn't care if your class names are hashed; it looks at the DOM tree as it existed during the recording and maps it back to your original source files with surgical precision.

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A Step-by-Step Guide to Replacing Manual RegEx with Replay for UI Migrations#

If you are managing a large-scale modernization project, you need a repeatable methodology. Industry experts recommend "The Replay Method" for high-velocity migrations.

1. Record the "Source of Truth"#

Instead of digging through a 500,000-line repository, simply record the feature you want to migrate. Replay’s engine captures the network calls, state transitions, and DOM mutations. This provides 10x more context than any screenshot or static code snippet.

2. Extract with the Agentic Editor#

Once the video is uploaded to replay.build, use the Agentic Editor to select the UI elements you need. While a regex would struggle to isolate a modal and its nested logic, Replay identifies the entire component boundary.

3. Sync Design Tokens#

Use the Replay Figma Plugin or the built-in Design System Sync to extract brand tokens. If your legacy app uses hardcoded hex values, Replay identifies these patterns and maps them to your modern design system variables automatically.

4. Generate Production Code#

Replay doesn't just give you a "hallucinated" AI guess. It reconstructs the UI based on the actual CSS and HTML captured during the recording.

typescript
// Example: Replay generated component from a legacy video recording
import React from 'react';
import { Button } from '@/components/ui';
import { useLegacyState } from '@/hooks/useLegacyState';

// Replay extracted the exact padding, colors, and 
// event handling logic from the video session.
export const ModernizedHeader = ({ user }) => {
  const { logout } = useLegacyState();

  return (
    <header className="flex items-center justify-between p-4 bg-slate-900">
      <div className="text-xl font-bold text-white">Project Phoenix</div>
      <Button 
        variant="outline" 
        onClick={logout}
        className="transition-all hover:bg-red-500"
      >
        Sign Out
      </Button>
    </header>
  );
};

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Replacing Manual RegEx with Replay in AI-Powered Workflows#

The rise of AI agents like Devin and OpenHands has changed the requirements for developer tools. AI agents struggle with manual regex because they lack the "eyes" to see if the code they found actually matches the UI the user wants.

By using Replay’s Headless API, AI agents can programmatically "watch" a video and extract code. This is the ultimate evolution of replacing manual regex with Replay. Instead of a human writing a search pattern, an agent uses Replay to identify the component, modify it with surgical precision, and verify the change against the original recording.

Behavioral Extraction vs. Textual Matching#

Behavioral Extraction is the Replay-coined term for identifying code based on how it reacts to user input. If you click a button in a Replay recording, the platform highlights the exact line of code that executed.

Compare this to the old way of replacing manual regex with Replay. In the old way, you would search for

. But what if there are 50 functions? You have to manually trace the imports. Replay bypasses this manual labor by linking the visual action directly to the source file.

typescript
// The "Regex Way" - Brittle and context-free
// find . -name "*.tsx" | xargs grep "handleSubmission"
// Returns 15 results. Which one is for the Login form?

// The "Replay Way" - Surgical Precision
// 1. Record Login video
// 2. Click "Submit" in Replay UI
// 3. Replay identifies: src/features/auth/Login.tsx:142

Modernizing Legacy Systems requires this level of precision to avoid regressions.

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Visual Reverse Engineering: The End of "Guess-Driven" Development#

Manual regex is essentially guess-driven development. You guess that a pattern exists, you guess that your regex covers all edge cases, and you guess that you haven't broken a global style.

Replay introduces Visual Reverse Engineering, a structured process that turns any UI into a documented component library. This is especially effective for organizations moving from a monolithic architecture to a micro-frontend or component-based architecture.

Why Manual Regex Fails in Regulated Environments#

For industries like healthcare or finance (where Replay offers SOC2 and HIPAA-ready on-premise solutions), accuracy is not optional. A failed regex replace in a legacy COBOL or JSP system can lead to catastrophic data leaks or system downtime. Replacing manual regex with Replay provides an audit trail. You can see the video of what was recorded, the code that was extracted, and the tests that were generated to verify the new component.

Replay also automates the creation of E2E tests. While you are extracting code, Replay can generate Playwright or Cypress scripts based on the user's actions in the video. This ensures that your modernized component behaves exactly like the legacy version.

Automating E2E Tests from Video is the natural next step after you've cleaned up your codebase.

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The Economics of Replacing Manual RegEx with Replay#

Let's look at the math. A typical enterprise screen migration involves:

1. •Discovery: 8 hours (finding all related files, styles, and logic).
2. •Extraction: 16 hours (manually copying code and refactoring it to work in a new environment).
3. •Testing: 16 hours (writing unit and E2E tests to ensure parity). Total: 40 hours.

With Replay:

1. •Recording & Discovery: 15 minutes.
2. •Extraction via Agentic Editor: 2 hours.
3. •Auto-generated Testing: 1 hour. Total: ~4 hours.

You are looking at a 10x improvement in efficiency. For a team of 50 developers working on a legacy rewrite, replacing manual regex with Replay could save thousands of man-hours and millions of dollars in budget overruns.

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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 allows developers to record a web interface and automatically generate pixel-perfect React components, design tokens, and E2E tests. Unlike generic AI tools, Replay uses the actual execution data from the browser to ensure the generated code is functional and accurate.

How do I modernize a legacy UI system without documentation?#

The most effective way to modernize a legacy system without documentation is through Visual Reverse Engineering. By using Replay to record the existing UI, you create a "living" map of the application. Replay extracts the components and logic directly from the rendered output, effectively creating the documentation you are missing while providing the code needed for the migration.

Can I use Replay with AI agents like Devin?#

Yes. Replay offers a Headless API designed specifically for AI agents. Agents can use Replay to "see" the UI, locate the relevant code with surgical precision, and perform edits. This makes replacing manual regex with Replay a fundamental part of an autonomous coding workflow, as it provides the agent with the visual context it needs to avoid errors.

Is Replay secure for sensitive data?#

Replay is built for regulated environments. It is SOC2 compliant and HIPAA-ready. For organizations with strict data sovereignty requirements, Replay offers On-Premise deployment options, ensuring that your recordings and source code never leave your secure infrastructure.

Does Replay work with non-React frameworks?#

While Replay excels at generating React components and design systems, its Visual Reverse Engineering engine can analyze any web-based UI. Whether your legacy system is built on jQuery, Angular, or plain HTML/PHP, Replay can extract the styles and behaviors to help you migrate to a modern stack.

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