Exercise 01: Write Your First CLAUDE.md

Concept: CLAUDE.md (CC-010) Level: Basic Time: ~10 minutes

Objective

Write a CLAUDE.md for a real project you own. By the end of this exercise, Claude will know who you are, what the project does, and how you want it to behave -- automatically, every session.

This is your first hands-on contact with CLAUDE.md. The only requirement is that you have a project directory with a few files in it.

Before You Start

Confirm you have:

Claude Code installed (claude --version prints a version)
A project directory you want to write a CLAUDE.md for
Claude Code open in that project directory

This exercise works best in your own project. If you do not have one handy, open Claude Code in any directory that has at least a few files.

Instructions

Step 1: Navigate to your project and open Claude Code.

cd /path/to/your-project
claude

Confirm there is no CLAUDE.md there yet:

ls CLAUDE.md

Expected output: ls: CLAUDE.md: No such file or directory

If a CLAUDE.md already exists, pick a different project for this exercise or rename the existing one temporarily (mv CLAUDE.md CLAUDE.md.bak).

Step 2: Think about three things before you run anything.

Who you are and what you care about when working on this project
What the project does in one sentence
Two or three rules that would save time if Claude knew them up front (examples: "always use TypeScript", "never modify files in dist/", "prefer short functions")

You do not need to write these down. Just have them in mind.

Step 3: Paste this prompt into Claude Code:

Look at this project. Read the files here, then write a CLAUDE.md for it.

The CLAUDE.md should include:
1. What this project is (one short paragraph, 2-3 sentences max)
2. How to work on it (language, framework, any tools)
3. Three specific rules I want you to follow in every session

For rule 3, use these rules I care about:
- [replace this with your first rule, e.g. "Never use var, always use const or let"]
- [replace this with your second rule, e.g. "All functions must have a JSDoc comment"]
- [replace this with your third rule, e.g. "Do not modify package.json without asking first"]

Keep it under 60 lines. No headers longer than one line. Plain and direct.

Replace the three placeholder rules with your own before pasting.

Step 4: Review what Claude writes and ask for one change.

Read the CLAUDE.md Claude produced. Find one thing that is off, vague, or missing, then ask Claude to fix it:

Change [the part that is wrong] to [what it should say].

This is a normal part of the process. CLAUDE.md files are written with Claude, not entirely by it.

Expected Output

After completing the steps above, you should see:

A CLAUDE.md file in your project root
It has a project description (not generic -- specific to your project)
It has your three rules stated clearly
It is under 60 lines total

If Claude produced something generic or padded, ask it to be more specific and shorter. Generic CLAUDE.md files provide almost no value.

What You Learned

CLAUDE.md is a briefing, not a manual: Give Claude the context it needs to behave like a new colleague who already knows your project
It is auto-loaded every session: You never have to paste it in or say "remember, we use TypeScript" again
Write it with Claude, not for Claude: Use Claude to read the project and draft the file, then you correct and sharpen it

Ready to see how CLAUDE.md files stack on top of each other? Move to Exercise 02: Hierarchy in Action.

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