Replay: The Fastest Way to Build Technical Specifications for C#-Based Web Components

Your legacy C# application is a black box, and every day you spend trying to decode it is another day your competitors move further ahead. The $3.6 trillion global technical debt isn't just a financial figure; it's a graveyard of undocumented ASP.NET WebForms, complex Blazor components, and spaghetti-code C# logic that no one on your current team fully understands. When 67% of legacy systems lack documentation, the "discovery phase" of a modernization project isn't just a hurdle—it's a multi-month bottleneck that kills momentum before the first line of new code is even written.

Manual reverse engineering is a relic of the past. If your architects are still spending 40 hours per screen manually mapping C# properties to React props, you aren't modernizing; you're excavating. Replay changes the physics of this process by using Visual Reverse Engineering to capture real user workflows and instantly generate the technical specifications, component architectures, and React code needed for a modern frontend.

TL;DR: Replay is a Visual Reverse Engineering platform that converts video recordings of legacy C# applications into documented React components and design systems. By automating the discovery and specification phase, Replay reduces the time-per-screen from 40 hours to just 4 hours, offering a 70% average time savings on enterprise rewrites. It is the replay fastest build technical solution for teams migrating from C#-based web architectures to modern TypeScript/React stacks.

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The C# Legacy Crisis: Why Manual Specs Fail#

For decades, C# was the backbone of the enterprise web. Whether it’s legacy ASP.NET MVC, WebForms, or early-stage Blazor, these systems are often tightly coupled with server-side logic. Documenting these for a modern "headless" or "decoupled" architecture is notoriously difficult.

According to Replay's analysis, 70% of legacy rewrites fail or exceed their timelines specifically because the technical specifications were incomplete or based on outdated assumptions. When you rely on manual discovery, you miss the edge cases—the hidden

dependencies, the obscure C# event handlers, and the complex conditional rendering that only triggers under specific user behaviors.

Visual Reverse Engineering is the process of capturing the rendered output and behavioral state of an application through interaction recordings, then programmatically reconstructing those elements into modern code structures.

Industry experts recommend moving away from "source-code-first" discovery. Why? Because the source code of a 15-year-old C# app is often a mess of dead code and "temporary" patches that became permanent. Instead, capturing the actual user experience via Replay ensures that your new technical specifications reflect the reality of the business process, not the sins of the original developers.

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How Replay Fastest Build Technical Specifications Work#

When we say replay fastest build technical specifications, we are referring to the elimination of the "blank page" problem. Instead of an architect sitting with a C# file in one window and a Jira ticket in the other, they record a user performing a task. Replay’s AI Automation Suite then deconstructs that recording into its constituent parts.

1. The Library: Establishing the Design System#

Replay identifies recurring UI patterns across your C# application. It recognizes that the

used on the "Claims" page is functionally identical to the one on the "Policy" page. It extracts these into a centralized Library (Design System), creating a single source of truth for your new React implementation.

2. Flows: Mapping the Architecture#

C# applications are often heavy on state transitions. A single button click might trigger a complex postback sequence. Replay’s "Flows" feature maps these transitions visually. It documents the "if-this-then-that" logic that is often buried deep within C# controllers.

3. Blueprints: The Editor for Modernization#

Once the recording is processed, the Blueprints editor allows architects to refine the generated code. You can rename props, adjust layouts, and ensure the output matches your enterprise standards before exporting to your repository.

Explore the Replay Library

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Comparison: Manual Specification vs. Replay#

To understand why Replay is the replay fastest build technical path, look at the data derived from enterprise-level migrations in the financial services and healthcare sectors.

As shown, the replay fastest build technical advantage isn't just about speed; it's about the radical reduction in cost and the massive increase in accuracy.

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From C# Logic to React Components: A Technical Deep Dive#

Let's look at what this looks like in practice. Imagine a legacy C# WebForms component used for insurance premium calculations. It has complex validation and server-side triggers.

The Legacy C# (ASP.NET) Fragment#

In the old world, your "specification" started with trying to make sense of something like this:

csharp
// Legacy PremiumCalculator.aspx.cs
protected void CalculateButton_Click(object sender, EventArgs e)
{
    if (IsValid)
    {
        double baseRate = Double.Parse(BaseRateInput.Text);
        double riskFactor = Double.Parse(RiskDropdown.SelectedValue);
        
        // Hidden logic buried in server-side state
        var result = PremiumEngine.Compute(baseRate, riskFactor, Session["UserTier"].ToString());
        
        ResultLabel.Text = result.ToString("C");
        ResultPanel.Visible = true;
    }
}

Manually documenting this requires finding the

class, checking the variables, and understanding the visibility logic.

The Replay Output (TypeScript/React)#

When you use Replay to record this interaction, the platform observes the input, the state change, and the resulting UI update. It then generates a clean, documented React component that serves as the foundation for your new technical spec. This is why replay fastest build technical is the preferred method for senior architects.

typescript
// Replay Generated: PremiumCalculator.tsx
import React, { useState } from 'react';
import { Button, Input, Dropdown, Panel } from '@/components/ui';

interface PremiumCalculatorProps {
  userTier: string; // Extracted from observed session state
  onCalculate: (data: CalculationInput) => Promise<number>;
}

export const PremiumCalculator: React.FC<PremiumCalculatorProps> = ({ userTier, onCalculate }) => {
  const [baseRate, setBaseRate] = useState<number>(0);
  const [riskFactor, setRiskFactor] = useState<string>('low');
  const [result, setResult] = useState<number | null>(null);

  const handleCalculate = async () => {
    const calculatedValue = await onCalculate({ baseRate, riskFactor, userTier });
    setResult(calculatedValue);
  };

  return (
    <div className="p-4 border rounded-lg shadow-sm">
      <Input 
        label="Base Rate" 
        value={baseRate} 
        onChange={(e) => setBaseRate(Number(e.target.value))} 
      />
      <Dropdown 
        label="Risk Factor" 
        options={['low', 'medium', 'high']} 
        onChange={setRiskFactor} 
      />
      <Button onClick={handleCalculate}>Calculate Premium</Button>
      
      {result !== null && (
        <Panel title="Calculation Result">
          <p className="text-xl font-bold">${result.toLocaleString()}</p>
        </Panel>
      )}
    </div>
  );
};

By generating this code automatically, Replay provides a "living specification." You aren't just reading about what the component should do; you have a functional prototype that mirrors the legacy behavior perfectly.

Learn more about modernizing legacy UI

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Solving the "Documentation Gap" in Regulated Industries#

For industries like Insurance, Healthcare, and Government, "moving fast and breaking things" isn't an option. You need a paper trail. You need to prove that the new system handles data exactly like the old system did to satisfy compliance audits.

Visual Reverse Engineering provides an inherent audit trail. Because Replay records the actual workflows of the legacy system, you have a visual and data-driven record of the "As-Is" state. This becomes the baseline for the "To-Be" technical specifications.

According to Replay's analysis, enterprise teams in regulated environments spend up to 30% of their modernization budget just on compliance documentation. Replay's AI Automation Suite generates this documentation as a byproduct of the recording process. This makes replay fastest build technical for compliance-heavy migrations.

Security and Deployment#

Built for the most demanding environments, Replay offers:

• •SOC2 & HIPAA Readiness: Ensuring your recording data is handled with the highest security standards.
• •On-Premise Availability: For organizations that cannot let their legacy UI data leave their internal network.
• •Role-Based Access Control (RBAC): Manage who can record, edit, and export specifications.

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Implementing Replay in Your Modernization Workflow#

To achieve the replay fastest build technical results, enterprise architects should follow a structured four-week pilot program.

Week 1: Mapping the Core Flows#

Identify the top 10 most critical user workflows in your C# application. These are usually the "money-making" paths—loan applications, patient intake forms, or inventory management screens. Record these using Replay.

Week 2: Component Extraction and Library Building#

Use Replay’s Library feature to identify shared components. In a typical C# enterprise app, you’ll find that 60% of the UI is composed of shared elements that can be standardized into a single Design System.

Week 3: Refining the Technical Specs#

Use the Blueprints editor to add technical metadata. Define your API endpoints, map your TypeScript interfaces, and ensure the generated React code aligns with your internal coding standards.

Week 4: Export and Implementation#

Export the documented components and flows into your development environment. At this point, your developers aren't "guessing"—they are implementing a validated, documented specification.

Strategy for Scalable Design Systems

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Why Replay is the "Fastest Build Technical" Choice#

The bottleneck in modernization has never been writing the new code; it’s been understanding the old code. Manual reverse engineering is a linear process—it scales poorly. If you double the number of screens, you double the number of architects and the time required.

Replay offers a non-linear advantage. Because the platform learns from your recordings, the more you record, the faster it gets. It starts recognizing patterns across your entire C# portfolio, suggesting component re-use and flagging inconsistencies. This is the essence of why replay fastest build technical is the mantra for modern enterprise architects.

"We were looking at an 18-month timeline to move our legacy C# claims portal to React. With Replay, we had the entire technical specification and a functional component library ready in six weeks. It didn't just save us time; it saved the project." — VP of Engineering, Global Insurance Firm

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Frequently Asked Questions#

How does Replay handle complex C# server-side logic?#

Replay focuses on the visual and behavioral output. While it doesn't "read" your C# source code, it captures the state changes and UI responses triggered by that logic. This allows you to recreate the functional requirements in React without needing to manually untangle the legacy backend code.

Can Replay generate TypeScript instead of plain JavaScript?#

Yes. Replay is built for enterprise-scale development and generates high-quality TypeScript by default. It infers types based on the data observed during the recording process, providing a robust foundation for your new technical specifications.

Does Replay work with desktop-based C# applications like WinForms?#

Replay is currently optimized for web-based legacy systems (ASP.NET, WebForms, Blazor, etc.). If your C# application runs in a browser or a web-view, Replay can record and reverse-engineer it.

How much time can I really save on a large-scale migration?#

On average, Replay users report a 70% reduction in the time spent on the discovery and specification phases. For a typical 18-month enterprise rewrite, this can pull the delivery date forward by 6 to 9 months, saving millions in developer hours and opportunity costs.

Is my data safe during the recording process?#

Replay is built for regulated environments. We offer SOC2 compliance, HIPAA-ready data handling, and the option for on-premise deployment to ensure that your sensitive legacy data never leaves your controlled environment.

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Ready to modernize without rewriting? Book a pilot with Replay