Codebase understanding is the most important developer skill nobody teaches. Schools teach algorithms. Bootcamps teach frameworks. Nobody teaches: "here's a 500K-line codebase you've never seen — figure out how to make a safe change."
This guide covers every technique and tool for understanding codebases, from basic to AI-powered.
Level 1: Manual Techniques
grep / ripgrep
The oldest tool. Search for text patterns across files. Fast and reliable for known terms. Useless for understanding structure or relationships.
IDE Navigation
Jump to definition, find references, peek at implementations. Essential for tracing individual call paths. Doesn't scale to understanding features or system-level behavior.