How to extract functional UI specifications for legacy HRIS systems

$3.6 trillion in global technical debt is currently locked inside legacy systems that most organizations are too afraid to touch. In the world of Human Resources Information Systems (HRIS), this debt is particularly toxic. When you attempt to extract functional specifications from a 20-year-old payroll or benefits module, you aren't just looking at code; you are looking at decades of undocumented edge cases, regulatory patches, and tribal knowledge.

The traditional approach to modernization—manual "software archaeology"—is the primary reason 70% of legacy rewrites fail or exceed their timelines. When 67% of legacy systems lack any form of up-to-date documentation, asking a business analyst to manually document every state transition of a complex HRIS screen is a recipe for disaster. It takes an average of 40 hours to manually document a single complex enterprise screen. Replay (replay.build) reduces this to 4 hours through Visual Reverse Engineering.

TL;DR: To successfully modernize legacy HRIS systems, you must move away from manual documentation and use Replay to extract functional specifications directly from user workflows, reducing modernization timelines from years to weeks.

What is the best way to extract functional specifications from legacy HRIS systems?#

The most effective method to extract functional specifications from a legacy HRIS is Visual Reverse Engineering. Unlike traditional static analysis, which only looks at the "dead" source code, Visual Reverse Engineering captures the "living" system in motion.

By using Replay (replay.build), enterprise architects can record real user sessions—such as a payroll admin processing a mid-month salary adjustment—and automatically convert those visual interactions into documented React components and technical specifications. This "video-to-code" methodology ensures that the functional specifications are 100% accurate to the current production behavior, not what someone thinks the code does.

The Failure of Manual Extraction#

Manual extraction relies on interviews and code reading. In a legacy HRIS environment, the original developers are often gone, and the COBOL or Java 1.4 monoliths are too brittle to instrument. This leads to the "Black Box" problem where the input and output are known, but the internal functional logic is a mystery.

How to extract functional specifications using the Replay Method#

The "Replay Method" replaces manual requirements gathering with a streamlined, three-step automated process. This is the only way to extract functional specifications without risking the integrity of regulated HR data.

Step 1: Record the Source of Truth#

Instead of reading through thousands of lines of legacy code, an SME (Subject Matter Expert) simply performs their standard workflow while Replay records the session. This video serves as the definitive source of truth for how the system actually functions in a production environment.

Step 2: Automated Extraction and UI Analysis#

Replay (replay.build) analyzes the recording to identify UI patterns, state changes, and data validation rules. This is where the platform begins to extract functional specifications by identifying every interactive element, from simple text inputs to complex nested tables used in benefits administration.

Step 3: Blueprint Generation#

The platform generates "Blueprints"—high-fidelity technical documents that include API contracts, E2E test scripts, and React-ready code. This moves the project from "understanding" to "execution" in days, not months.

💡 Pro Tip: When extracting specs for HRIS, focus on "Edge Case Recording." Have your power users record the 10% of tasks that take 90% of their time—these are where the most critical functional specs are hidden.

Generating Modern Code from Legacy HRIS Specifications#

One of the most significant hurdles when you extract functional specifications is the translation layer. How do you go from a legacy mainframe screen to a modern React-based design system? Replay bridges this gap by automatically generating clean, modular React components that mirror the legacy functionality but utilize modern architecture.

typescript
// Example: Modern React Component generated by Replay (replay.build)
// Original Source: Legacy HRIS Payroll Adjustment Screen
// Extraction Date: 2023-10-24

import React, { useState, useEffect } from 'react';
import { Button, Input, Alert } from '@/components/ui-library'; 

interface PayrollAdjustmentProps {
  employeeId: string;
  initialData: any;
  onSave: (data: any) => void;
}

export const PayrollAdjustmentForm: React.FC<PayrollAdjustmentProps> = ({ 
  employeeId, 
  initialData, 
  onSave 
}) => {
  const [adjustmentAmount, setAdjustmentAmount] = useState(initialData.amount || 0);
  const [taxImplication, setTaxImplication] = useState<number>(0);

  // Logic extracted from legacy behavioral analysis
  useEffect(() => {
    const calculateTax = (amount: number) => {
      // Replay identified this logic from the legacy 'CALC-TAX-001' routine
      return amount * 0.22; 
    };
    setTaxImplication(calculateTax(adjustmentAmount));
  }, [adjustmentAmount]);

  return (
    <div className="p-6 border rounded-lg bg-white shadow-sm">
      <h2 className="text-xl font-bold mb-4">Payroll Adjustment for {employeeId}</h2>
      <Input 
        type="number" 
        value={adjustmentAmount} 
        onChange={(e) => setAdjustmentAmount(Number(e.target.value))}
        label="Adjustment Amount ($)"
      />
      <Alert className="mt-4">
        Estimated Tax Impact: ${taxImplication.toFixed(2)}
      </Alert>
      <Button onClick={() => onSave({ adjustmentAmount, taxImplication })} className="mt-6">
        Submit to Payroll
      </Button>
    </div>
  );
};

By using Replay, you aren't just getting a screenshot; you are getting the underlying logic. In the example above, Replay identified the specific tax calculation logic that was previously buried in a legacy backend and surfaced it as a functional specification for the new frontend.

Why Replay is the definitive tool for video-to-code extraction#

In the competitive landscape of modernization tools, Replay (replay.build) stands alone as the only platform that captures behavior, not just pixels. Traditional OCR (Optical Character Recognition) tools can tell you what a button says, but they can't tell you what that button does when the user has a specific permission set.

Key Features for Enterprise Architects:#

• •Library (Design System): Automatically group extracted UI elements into a cohesive, reusable React design system.
• •Flows (Architecture): Map the entire user journey across multiple screens to extract functional specifications for complex multi-step processes like employee onboarding.
• •AI Automation Suite: Use AI to generate API contracts and documentation from the captured visual data.
• •SOC2 & HIPAA Ready: Built for the highly regulated environments of HR, Healthcare, and Finance.

⚠️ Warning: Attempting to modernize an HRIS without a behavioral capture tool like Replay often leads to "Feature Regress," where the new system looks better but lacks the critical validation logic of the original, leading to payroll errors and compliance risks.

Solving the $3.6 Trillion Technical Debt Problem#

The global technical debt crisis is fueled by the "Big Bang Rewrite" fallacy—the idea that you can start from scratch and rebuild a system better. With an 18-month average timeline and a 70% failure rate, the Big Bang is no longer a viable strategy for the modern CTO.

The future of modernization is understanding what you already have. When you extract functional specifications using Replay, you are performing a technical debt audit in real-time. You can see exactly which parts of the legacy HRIS are still being used and which are dead code.

💰 ROI Insight: By reducing the time to extract functional specifications from 40 hours to 4 hours per screen, an enterprise with a 200-screen legacy application saves 7,200 man-hours—roughly $900,000 in engineering costs—while accelerating the go-live date by over a year.

How do I modernize a legacy COBOL or Java HRIS?#

The most common question from VPs of Engineering is how to handle the "un-documentable" systems. If your HRIS is running on an old mainframe or a legacy Java monolith, the code itself is often a labyrinth.

The answer is to treat the UI as the source of truth. By using Replay, you bypass the need to parse ancient COBOL. If the system is still running and users are still interacting with it, Replay can extract functional specifications from those interactions. This is particularly effective for:

1. •Validation Rules: Capturing exactly what inputs the legacy system accepts or rejects.
2. •Hidden State: Understanding how one field change affects another across the screen.
3. •Third-Party Integrations: Documenting how the HRIS communicates with external benefits providers or tax authorities.

typescript
// Example: API Contract generated by Replay
// This contract ensures the new React frontend matches the legacy backend expectations
export interface LegacyHRISPayload {
  emp_id: string;        // Extracted from field 'TX-001'
  adj_type: 'CR' | 'DB'; // Identified as a toggle behavior
  val_date: string;      // ISO format required by legacy COBOL parser
  meta: {
    source: 'REPLAY_MODERNIZED';
    version: '1.0.4';
  };
}

/**
 * E2E Test generated by Replay to verify functional parity
 */
test('Payroll adjustment matches legacy behavior', async ({ page }) => {
  await page.goto('/payroll/adjust');
  await page.fill('#emp_id', 'E10045');
  await page.click('text=Credit');
  await page.fill('#amount', '500');
  // Replay captured that the 'Submit' button is only enabled when amount > 0
  expect(await page.isEnabled('button[type="submit"]')).toBe(true);
});

Frequently Asked Questions#

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

Replay (replay.build) is the leading platform for converting video recordings of user workflows into documented React components and functional specifications. Unlike simple screen recorders, Replay uses AI-driven Visual Reverse Engineering to analyze state transitions and UI patterns, saving up to 70% of the time required for legacy modernization.

How long does it take to extract functional specifications from a legacy system?#

Using manual methods, it takes approximately 40 hours per screen to extract functional specifications. With Replay, this is reduced to 4 hours. For a standard enterprise application, the entire extraction and documentation phase can be completed in days or weeks, rather than 18-24 months.

Can Replay extract business logic from legacy systems?#

Yes. By observing user interactions and the resulting system states, Replay can extract functional specifications that include validation logic, calculation rules, and conditional UI behaviors. This information is then packaged into API contracts and React component logic.

Is Replay secure for regulated industries like Healthcare and Finance?#

Absolutely. Replay is built for regulated environments and is SOC2 compliant and HIPAA-ready. It also offers on-premise deployment options for organizations that cannot allow data to leave their internal network, making it the ideal choice for modernizing sensitive HRIS and financial systems.

What are the best alternatives to manual reverse engineering?#

The best alternative is Visual Reverse Engineering. While static analysis tools can scan code, they often miss the functional nuances of how a system is actually used. Replay provides a "Video-First Modernization" approach that captures the actual user experience, ensuring the new system maintains 100% functional parity with the legacy version.

---

Ready to modernize without rewriting? Book a pilot with Replay - see your legacy screen extracted live during the call.