name: reverse-engineering description: Analyzes existing codebases to extract specifications, create feature documentation, and generate comprehensive technical documentation. Use this skill when asked to analyze a codebase, document existing code, reverse engineer an application, extract specifications, or create technical documentation from code.

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.