Reverse Engineering Skill

This skill comprehensively analyzes existing codebases and extracts specifications, feature documentation, and technical documentation to serve as a foundation for modernization efforts.

When to Use This Skill

• •Analyzing an existing codebase
• •Extracting specifications from legacy code
• •Creating technical documentation from code
• •Preparing for modernization or migration
• •Understanding undocumented systems

Critical Rules

What You Must NEVER Do

1. •NEVER modify, create, or change ANY code - Documentation ONLY
2. •NEVER make things up - Document ONLY what actually exists
3. •NEVER create specs/prd.md - That is PM's responsibility
4. •NEVER fabricate details - If it doesn't exist, say so
5. •NEVER assume missing implementations - Be honest about gaps

What You Must Do

1. •Document what EXISTS - Analyze the actual implementation as-is
2. •Be honest about gaps - Explicitly state missing or incomplete elements
3. •Map to real code - Every finding must reference actual files
4. •Accept any tech stack - Work with whatever the project uses
5. •Be comprehensive - Leave no stone unturned

Analysis Workflow

Phase 1: Discovery and Inventory

1. Repository Discovery

• •Read configuration files (package.json, requirements.txt, .csproj, etc.)
• •Examine project structure and directory purposes
• •Identify entry points and startup configurations
• •Catalog build and deployment configurations

2. Technology Stack Mapping

• •Detect all programming languages used
• •Identify frameworks, ORMs, testing frameworks
• •Inventory build tools and package managers
• •Capture versions where possible

Phase 2: Feature Extraction

3. Feature Discovery

• •Identify all user-facing features and pages
• •Document all API endpoints and functionality
• •Extract core business processes
• •Examine database schemas and data structures

4. Business Feature Analysis

Create individual files in specs/features/ with:

• •Feature purpose and business problem solved
• •User workflows and interactions
• •Functional requirements
• •Acceptance criteria (from observable behavior)
• •Dependencies on other features
• •Implementation status (complete/partial/missing)

Phase 3: Technical Deep Dive

5. Architecture Assessment

• •Map component relationships and interactions
• •Trace data flow through the system
• •Identify external system connections
• •Document architectural and design patterns

6. Quality Assessment

• •Evaluate existing test coverage
• •Assess documentation completeness
• •Identify maintainability issues
• •Document security patterns and concerns

Documentation Structure to Create

specs/
├── features/                    # Feature Requirements Documents
│   ├── [feature-1].md
│   ├── [feature-2].md
│   └── ...
└── docs/
    ├── architecture/
    │   ├── overview.md          # System architecture overview
    │   ├── components.md        # Component relationships
    │   ├── patterns.md          # Design patterns used
    │   └── security.md          # Security patterns
    ├── technology/
    │   ├── stack.md             # Complete technology inventory
    │   ├── dependencies.md      # All dependencies with versions
    │   └── tools.md             # Build and dev tools
    ├── infrastructure/
    │   ├── deployment.md        # Deployment architecture
    │   ├── environments.md      # Environment configurations
    │   └── operations.md        # Operational procedures
    └── integration/
        ├── apis.md              # API documentation
        ├── databases.md         # Database schemas
        └── services.md          # External services

Success Criteria

Analysis is complete when:

• •✅ Complete documentation structure created
• •✅ All major features identified and documented
• •✅ Technology stack completely mapped
• •✅ Architecture clearly documented
• •✅ Dependencies catalogued
• •✅ Integration points mapped
• •✅ Code quality assessed honestly
• •✅ Everything linked to actual code files

Next Steps

After analysis is complete:

• •Hand off to Modernizer Agent for modernization planning
• •Feature documentation guides functionality preservation
• •Technical assessment informs priorities and risk management

Templates

See templates/ for documentation templates.

Sample Output

See examples/sample-analysis-output.md for a complete example.