Drive to Legacy - Systematic Legacy Code Exploration

Overview

A 6-phase systematic approach to fully understand an unfamiliar codebase, producing a comprehensive architecture document with mermaid diagrams that both humans and AI can use for porting, migration, or onboarding.

Core principle: Explore wide before deep. Map the full territory first, then drill into each layer. Every finding goes into a living ARCHITECTURE.md with diagrams.

When to Use

• Onboarding to an unfamiliar codebase
• Preparing to port or rewrite an application
• Documenting a legacy system that lacks documentation
• Studying code you need to maintain but did not write
• Any "how does this work?" question about a full project