Chapter 05 · Daily driving

CLAUDE.md & memory

Every conversation starts fresh; Claude forgets yesterday. CLAUDE.md fixes that: a plain text file of standing instructions that Claude reads at the start of every session. Write it once, benefit forever.

Let Claude write it: /init

Type /init and Claude studies your project, then drafts a CLAUDE.md for you. Edit it any time with /memory or like any normal file.

What goes in it

The golden test, straight from the official guide: for each line ask "would removing this cause Claude to make mistakes?" If not, cut it. Long files get ignored.

✓ Put in

How to run and test the project · rules that differ from the norm · things that burned you before · "always ask before X"

✗ Leave out

Anything Claude can see by reading the code · long tutorials · obvious advice like "write good code"

A good CLAUDE.md is this short

# Portfolio tracker

## Run it
Open index.html in a browser. No build step.

## Rules
- Files in data/ are broker exports: read them, never edit them
- Show money with 2 decimals and a thousands separator
- I'm a beginner: explain changes in plain English

Where it lives

File	Applies to
`CLAUDE.md` in your project	This project, shared with teammates if you use git
`CLAUDE.local.md`	This project, just you
`~/.claude/CLAUDE.md`	Every project on your computer (your personal preferences)

Save thoughts mid-chat with #

Notice something worth remembering while working? Start a message with #:

Automatic memory

Claude also keeps its own notebook: things it learns about your project (which commands work, what you corrected it on) get saved automatically and recalled next session. Browse or edit it with /memory. It's all plain text; nothing is hidden.

✳

If Claude keeps ignoring a rule, your CLAUDE.md is probably too long and the rule is drowning. Prune it. For rules that must happen every single time, use a hook instead; hooks can't be forgotten.

✳ Try it yourself

/init

Read what it wrote. Delete half of it. That's usually the right length.