The 30-Day Legacy Assessment: A Practical Framework for Rapid Discovery

The average enterprise rewrite takes 18 to 24 months, yet 70% of these projects either fail outright or significantly exceed their original timelines. This isn't a failure of engineering talent; it’s a failure of discovery. We treat legacy systems like archaeological sites, spending months digging through undocumented COBOL or spaghetti jQuery, hoping to find the "source of truth."

The truth isn't in the code. The code is a graveyard of decade-old decisions. The truth is in the workflow—how the user interacts with the system today.

TL;DR: The 30-Day Legacy framework replaces months of manual "code archaeology" with automated visual reverse engineering, using Replay to compress discovery and component extraction from 18 months down to four weeks.

The Archaeology Trap: Why Discovery Stalls#

Most modernization projects stall in the "Assessment Phase." Architects spend hundreds of hours interviewing subject matter experts (SMEs) who have forgotten why certain logic exists, or worse, have left the company.

When you lack documentation—which is the case for 67% of legacy systems—you are forced to perform manual extraction. This process typically consumes 40 hours per screen just to document the state, logic, and API requirements. Across a 50-screen application, that’s 2,000 hours of high-priced engineering time spent just looking backward.

The 30-Day Legacy Framework#

To modernize without the "Big Bang" risk, you need a rapid, repeatable framework. This 30-day approach focuses on understanding what you have by recording what it does.

Phase 1: Workflow Inventory (Days 1–7)#

Identify the high-value "Golden Paths." In financial services, this might be the loan approval flow; in healthcare, the patient intake process. Instead of reading code, record the users.

1. •Identify Stakeholders: Gather the power users who live in the legacy system daily.
2. •Define the Scope: Select the top 20% of screens that handle 80% of the business value.
3. •Capture the Truth: Use Replay to record real user sessions. This creates a visual and technical record of every state change, API call, and UI transition.

💰 ROI Insight: By recording workflows instead of interviewing SMEs, enterprises save an average of 150 man-hours in the first week alone.

Phase 2: Visual Reverse Engineering (Days 8–15)#

Once the workflows are recorded, the "Black Box" begins to open. Replay’s engine analyzes the recordings to extract the underlying architecture.

During this phase, we move from video to code. Replay identifies patterns in the legacy UI and maps them to modern React components. This isn't just a screenshot; it's a functional decomposition of the frontend.

typescript
// Example: Replay-generated React component from a legacy Insurance Claim screen
// The logic is preserved, but the implementation is modernized to TypeScript/React.

import React, { useState, useEffect } from 'react';
import { ClaimService } from '@/services/legacy-bridge';
import { Button, Input, Card } from '@/components/ui-library';

export const ClaimAdjustmentForm = ({ claimId }: { claimId: string }) => {
  const [data, setData] = useState<any>(null);
  const [loading, setLoading] = useState(true);

  // Replay identified this specific validation logic from the legacy event loop
  const validateAdjustment = (amount: number) => {
    return amount > 0 && amount < 50000; 
  };

  useEffect(() => {
    // Replay extracted the exact API endpoint and payload structure
    ClaimService.getDetails(claimId).then(res => {
      setData(res);
      setLoading(false);
    });
  }, [claimId]);

  if (loading) return <Spinner />;

  return (
    <Card title={`Adjusting Claim: ${data?.policyNumber}`}>
      <Input 
        label="Adjustment Amount" 
        type="number" 
        onChange={(e) => {/* ... */}} 
      />
      <Button onClick={() => {/* ... */}}>Submit to Underwriting</Button>
    </Card>
  );
};

Phase 3: API Contract & Test Generation (Days 16–23)#

The biggest risk in modernization is breaking the contract between the frontend and the backend. If you don't know the exact JSON payload the legacy system expects, your new system will fail on day one.

Replay automatically generates API contracts and E2E tests based on the recorded traffic. This creates a "Safety Net" for the migration.

• •API Contracts: Automatically generated Swagger/OpenAPI specs from legacy traffic.
• •E2E Tests: Playwright or Cypress scripts that replicate the exact user flow.
• •State Mapping: Documentation of how data transforms across the workflow.

⚠️ Warning: Never attempt a rewrite without a captured API contract. Guessing the data types of a 20-year-old mainframe response is the fastest way to blow a budget.

Phase 4: The Modernization Roadmap (Days 24–30)#

The final week is about synthesis. You now have:

1. •A library of documented React components.
2. •A full map of all API dependencies.
3. •A technical debt audit identifying the "messiest" parts of the legacy logic.

This data allows you to move from a "Big Bang" rewrite to a Strangler Fig approach. You can replace one screen or one component at a time, knowing exactly how it fits into the whole.

The Economics of Modernization#

Global technical debt is estimated at $3.6 trillion. Most of that cost is "interest" paid in the form of slow feature velocity. When you use Replay to automate the discovery phase, you are essentially refinancing that debt.

Case Study: Financial Services Migration#

A Tier-1 bank attempted to modernize their commercial lending portal. After 12 months and $4M spent on manual discovery, they had 400 pages of Word documents but zero lines of modern code.

Using the 30-Day Legacy framework with Replay:

• •Week 1: Recorded 45 core workflows.
• •Week 2: Extracted 120 reusable React components into a Design System (Library).
• •Week 3: Generated OpenAPI specs for 85 legacy endpoints.
• •Week 4: Produced a production-ready "Blueprint" for the first phase of the rollout.

Total Savings: 70% reduction in time-to-market and a 90% reduction in manual documentation costs.

Technical Implementation: From Video to Blueprint#

Replay doesn't just "show" you the legacy system; it parses the DOM and network layers during recording to build a Blueprint. This Blueprint serves as the source of truth for your engineering team.

json
{
  "screen": "AccountSummary",
  "legacy_tech_stack": "ASP.NET WebForms",
  "extracted_logic": {
    "currency_conversion": "function(val, rate) { return val * rate; }",
    "permission_check": "user.role === 'ADMIN' && account.status === 'ACTIVE'"
  },
  "dependencies": [
    {
      "type": "API",
      "endpoint": "/api/v1/accounts/{id}",
      "method": "GET",
      "response_schema": "AccountSchema_v2"
    }
  ],
  "components_generated": ["AccountHeader", "BalanceGrid", "TransactionHistory"]
}

By having this structured data, your developers can focus on building rather than investigating.

📝 Note: Replay is built for regulated environments. Whether you are in Healthcare (HIPAA) or Government, the platform supports On-Premise deployment and SOC2 compliance to ensure your recording data remains secure.

Frequently Asked Questions#

How does Replay handle complex business logic hidden in the backend?#

Replay records the inputs and outputs of that logic. While it won't "read" your COBOL, it will document exactly what the COBOL expects and what it returns. This allows you to treat the legacy backend as a black box while you build the modern interface, or use the generated API contracts to rewrite the backend services with 100% confidence.

Can we use Replay for internal tools with no documentation?#

This is the primary use case. Internal tools are often the most undocumented and technically "crusty." Replay acts as the documentation layer that was never written, turning user behavior into a technical specification.

Does this replace our existing developers?#

No. It empowers them. Instead of your senior architects spending 80% of their time "spelunking" through old code, they spend 100% of their time designing the future architecture. It moves them from "archaeologists" to "architects."

What is the typical time savings?#

We see an average of 70% time savings across the modernization lifecycle. The most dramatic shift is in the discovery phase, where the 18-month "Big Bang" timeline is compressed into weeks.

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