CLAUDE.md - how to set up project instructions for Claude Code

My CLAUDE.md is 216 lines long. It references 13 separate rule files. It has a section called "How to Work With Mateusz" that includes gems like "Do not soften truth" and "When he says change X, change exactly X. Not Y. Not X and also improved Z. Just X." I also have a file called lessons-learned.md where Claude automatically logs every mistake it makes. There are 20+ entries. One of them is about a hover color where Claude guessed #404040 instead of looking up the actual token. The real value was #737373 . Darker instead of lighter. Claude was too lazy to check, and I was too trusting to notice until it looked wrong. This is what happens when you take CLAUDE.md seriously. You end up building a relationship with a tool that forgets you exist every time you close the terminal. The week the internet said to delete it A study from ETH Zurich tested four coding agents on hundreds of real tasks. With instruction files and without. /init makes things worse. Agents using auto-generated files