Visual Behavior Synthesis: The Fastest Way to Onboard Teams to 15-Year-Old Codebases

Your lead architect just resigned, and they were the only person who understood how the 15-year-old claims processing engine actually calculates interest. This is the "Legacy Archaeology" trap: a high-stakes environment where 67% of legacy systems lack any meaningful documentation, and the source code has become a sedimentary layer of hotfixes and abandoned patterns. When a new team inherits this, they don't spend their first month coding; they spend it guessing.

Visual behavior synthesis fastest paths to productivity don't involve reading thousands of lines of undocumented COBOL or jQuery; they involve capturing the "truth" of the application as it lives in the browser or terminal today. By recording real user workflows and translating those visual interactions into documented React code, we bypass the tribal knowledge gap entirely.

TL;DR:

• •The Problem: Traditional onboarding to 15-year-old codebases takes 6-9 months due to $3.6 trillion in global technical debt and missing documentation.
• •The Solution: Visual Behavior Synthesis uses video-to-code technology to map legacy UI interactions directly to modern React components.
• •The Result: Replay reduces the manual reverse engineering time from 40 hours per screen to just 4 hours, offering a 70% average time saving on modernization.
• •Key Takeaway: Stop reading dead code. Start recording live behavior to generate your new Design System and Architecture automatically.

The Archaeology Problem: Why Manual Onboarding Fails#

According to Replay's analysis, the average enterprise rewrite timeline spans 18 to 24 months, yet 70% of these projects either fail entirely or significantly exceed their original scope. The bottleneck isn't the talent of the developers; it's the "Information Decay" inherent in systems built over a decade ago.

When a developer joins a project with a 15-year-old codebase, they face three primary hurdles:

1. •Dead Code vs. Active Code: In a million-line monolith, which 10% of the code is actually driving the mission-critical workflows?
2. •Implicit Business Logic: Rules that were never written in a spec but exist as "hacks" in the UI layer to compensate for backend limitations.
3. •Fragmented State Management: Global variables, hidden DOM attributes, and side effects that make the system impossible to trace.

Industry experts recommend moving away from "source-first" discovery. Instead, visual behavior synthesis fastest methodologies prioritize the user's journey as the primary source of truth. If the system does it on screen, it must be represented in the code—regardless of how messy the underlying legacy implementation is.

Video-to-code is the process of recording a user performing a specific task in a legacy application and using AI-driven visual analysis to generate a clean, modular React component library that mirrors that behavior perfectly.

Implementing Visual Behavior Synthesis Fastest Onboarding Strategies#

To move from a recording to a functional React component library, you need a structured pipeline. This is where Replay excels, transforming raw video data into a structured "Flow" and eventually a "Blueprint."

Step 1: Capturing the "Truth"#

Instead of handing a new developer a GitHub link and a prayer, you provide them with a library of recorded workflows. These recordings capture every hover state, every validation error, and every complex data table interaction.

Step 2: Synthesis and Component Extraction#

The synthesis engine looks at the visual changes and identifies repeating patterns. In a 15-year-old system, "Buttons" might be implemented in six different ways. Visual synthesis identifies that these are functionally identical and maps them to a single, unified Design System component.

Step 3: Generating the Modern Equivalent#

Here is the difference between legacy spaghetti and modern synthesis. Below is a representation of what a developer might find in a 2009-era ASP.NET or jQuery application versus the output generated by Replay.

Legacy Code (The "Before")

javascript
// Found in a 4,000 line file: global_functions.js
function validateAndSubmit() {
    var val = $('#claimAmount').val();
    if (val > 1000) {
        $('.warning-div').show();
        document.getElementById('status_icon').src = '/assets/red_dot.png';
        // Why is this global? Nobody knows.
        window.is_high_value = true;
    }
    // Direct DOM manipulation mixed with business logic
    doLegacyAjaxPost('/api/v1/save-claims', {amt: val, type: window.claim_type});
}

Synthesized React Component (The "After" via Replay)

typescript
import React, { useState } from 'react';
import { Button, Input, Alert } from '@/components/ui';
import { useClaimsStore } from '@/store/claims';

interface ClaimFormProps {
  initialAmount?: number;
  onSuccess: (data: any) => void;
}

/**
 * Generated via Visual Behavior Synthesis
 * Original Workflow: "High Value Claim Submission"
 */
export const ClaimForm: React.FC<ClaimFormProps> = ({ initialAmount = 0, onSuccess }) => {
  const [amount, setAmount] = useState(initialAmount);
  const isHighValue = amount > 1000;

  const handleSubmit = async () => {
    const response = await fetch('/api/v2/claims', {
      method: 'POST',
      body: JSON.stringify({ amount, isHighValue }),
    });
    if (response.ok) onSuccess(await response.json());
  };

  return (
    <div className="p-6 space-y-4">
      <Input 
        type="number" 
        value={amount} 
        onChange={(e) => setAmount(Number(e.target.value))} 
        label="Claim Amount"
      />
      {isHighValue && (
        <Alert variant="warning" title="High Value Claim Detected">
          This claim requires additional supervisor approval.
        </Alert>
      )}
      <Button onClick={handleSubmit}>Submit Claim</Button>
    </div>
  );
};

Comparison: Manual vs. Visual Behavior Synthesis#

When evaluating the visual behavior synthesis fastest route, the data speaks for itself. Manual modernization is a linear struggle against technical debt, whereas visual reverse engineering is an exponential accelerator.

For more on how this impacts long-term maintenance, see our guide on legacy modernization strategies.

The Replay Architecture: Flows, Blueprints, and Library#

To achieve the visual behavior synthesis fastest results, Replay utilizes a three-tier architecture that organizes legacy knowledge into actionable code.

1. Flows (The Architecture)#

Flows map the user's journey across multiple screens. In a 15-year-old codebase, navigation logic is often hidden in obscure server-side redirects. Replay captures these transitions visually, creating an architectural map that shows exactly how data moves from Page A to Page B.

2. Blueprints (The Editor)#

Blueprints allow architects to refine the synthesized components. If the AI identifies a complex data grid, the Blueprint editor lets you map specific legacy data fields to modern TypeScript interfaces. This ensures the generated code isn't just "pretty UI" but functional, type-safe software.

3. Library (The Design System)#

The Library is the final destination. It acts as a living Design System for your modernized application. Instead of building a component library from scratch—which can take 6 months—Replay populates your library automatically based on the visual patterns it synthesized from your recordings.

Explore the Replay Library features to see how we handle complex enterprise UI components.

Why Regulated Industries Choose Visual Synthesis#

In sectors like Financial Services, Healthcare, and Government, "just rewriting it" isn't an option. The risk of losing a specific regulatory check buried in the UI logic is too high.

Visual behavior synthesis provides an audit trail. Because the React code is generated directly from a recording of the legacy system performing the task, you have visual proof that the new system matches the old system's behavior. Replay is built for these environments, offering SOC2 compliance, HIPAA-readiness, and On-Premise deployment options for air-gapped modernization.

According to Replay's analysis, healthcare organizations using visual synthesis reduced their compliance-related rework by 55% compared to manual rewrites.

The Technical Implementation of Visual Synthesis#

How does the "synthesis" actually happen? It involves a multi-stage AI pipeline:

1. •Computer Vision Layer: Identifies UI boundaries, typography, and spacing.
2. •Behavioral Analysis Layer: Observes how the UI reacts to input (e.g., "When this button is clicked, a modal appears").
3. •Code Generation Layer: Translates those visual observations into clean, functional React code using modern best practices (Tailwind CSS, TypeScript, Headless UI).

typescript
// Example of a synthesized "Smart Table" from a legacy mainframe-style UI
import { useTable } from '@/hooks/useTable';

export const LegacyDataGrid = ({ dataSourceUrl }: { dataSourceUrl: string }) => {
  // Replay detected this table has sorting, pagination, and a "Export to Excel" feature
  const { data, sort, paginate, exportData } = useTable(dataSourceUrl);

  return (
    <div className="border rounded-lg overflow-hidden shadow-sm">
      <table className="min-w-full divide-y divide-gray-200">
        <thead className="bg-gray-50">
          <tr>
            <th onClick={() => sort('id')}>ID</th>
            <th onClick={() => sort('name')}>Claimant</th>
            <th onClick={() => sort('status')}>Status</th>
          </tr>
        </thead>
        <tbody className="bg-white divide-y divide-gray-200">
          {data.map((row) => (
            <tr key={row.id}>
              <td>{row.id}</td>
              <td>{row.name}</td>
              <td>
                <StatusBadge type={row.status} />
              </td>
            </tr>
          ))}
        </tbody>
      </table>
      <Pagination onPageChange={paginate} />
    </div>
  );
};

By using the visual behavior synthesis fastest approach, developers don't have to worry about the underlying 2,000-line

file. They only care about the visual output and the data contract, which Replay has already documented for them.

Learn more about our AI-driven automation suite and how it handles complex data structures.

Overcoming the $3.6 Trillion Technical Debt#

Technical debt is often described as "interest" paid on past shortcuts. In a 15-year-old codebase, that interest has compounded to the point of bankruptcy. Visual Behavior Synthesis is a "debt restructuring" tool. It allows you to extract the value (the business logic and user experience) without taking on the liability (the legacy code).

Industry experts recommend a "Strangler Fig" pattern for modernization—gradually replacing legacy pieces with modern ones. Visual Behavior Synthesis accelerates this by providing the modern pieces (React components) instantly.

Case Study: Financial Services Modernization#

A Tier-1 bank had a 12-year-old internal trading portal. Onboarding a new engineer took 5 months. By implementing Replay, they recorded the 50 most critical workflows. Within 3 weeks, they had a fully documented React component library and a new architecture map. The onboarding time for the next cohort of engineers dropped to 14 days.

Frequently Asked Questions#

What is visual behavior synthesis?#

Visual behavior synthesis is the process of using AI and computer vision to record user interactions within an application and automatically translate those behaviors into modular, documented code (like React). It bridges the gap between what a user sees on the screen and the underlying logic required to recreate it in a modern framework.

Why is visual behavior synthesis the fastest way to onboard teams?#

It eliminates the need for "code archaeology." Instead of spending months reading undocumented legacy source code, new developers can watch recorded workflows and immediately work with clean, auto-generated React components that mirror the legacy system's behavior. This reduces the learning curve from months to weeks.

Can visual behavior synthesis handle complex backend logic?#

While the synthesis primarily focuses on the UI and frontend behavior, Replay maps the data contracts between the frontend and backend. This allows developers to see exactly what API calls are being made, what data is sent, and how the UI responds, making it much easier to modernize the backend services in tandem.

Is Replay secure for highly regulated industries?#

Yes. Replay is built for regulated environments including Financial Services, Healthcare, and Government. It is SOC2 compliant, HIPAA-ready, and offers On-Premise deployment options to ensure that sensitive data and proprietary code never leave your secure environment.

How does Replay handle custom or non-standard legacy UI components?#

Replay’s AI Automation Suite is trained to recognize functional patterns rather than just specific code snippets. Whether your legacy system uses custom ActiveX controls, old Delphi components, or obscure jQuery plugins, Replay analyzes the visual output and interaction pattern to synthesize a modern, functional equivalent in React.

Conclusion: Stop Reading, Start Recording#

The traditional approach to legacy modernization is broken. You cannot solve a 15-year-old documentation problem by asking your current developers to work harder. The visual behavior synthesis fastest path to success is to stop treating the legacy codebase as the source of truth and start treating the application behavior as the source of truth.

With Replay, you can turn your legacy "black box" into a transparent, documented, and modern React ecosystem in a fraction of the time. Don't let your technical debt hold your team hostage.

Ready to modernize without rewriting? Book a pilot with Replay