# Exercise 02: Hierarchy in Action

**Concept:** CLAUDE.md (CC-010)
**Level:** Intermediate
**Time:** ~15 minutes

---

## Objective

See how global, project, and subdirectory CLAUDE.md files work together.
Claude reads all three and applies them simultaneously, with more specific
files taking precedence over broader ones.

Exercise 01 covered a single CLAUDE.md. This exercise shows the full stack.

---

## Before You Start

Confirm you have:

- [ ] Completed Exercise 01 (or understand what CLAUDE.md does)
- [ ] Claude Code open in this repo directory

**Important:** This exercise creates a file at `~/.claude/CLAUDE.md`, which
is your global Claude Code configuration. If you already have one, back it up first:

```bash
cp ~/.claude/CLAUDE.md ~/.claude/CLAUDE.md.bak
```

Restore it after the exercise with:

```bash
mv ~/.claude/CLAUDE.md.bak ~/.claude/CLAUDE.md
```

---

## Instructions

**Step 1:** Create a global CLAUDE.md with a personal preference.

This file applies to every project you open with Claude Code, everywhere.

```bash
mkdir -p ~/.claude
```

Then paste this prompt into Claude Code:

```
Create a file at ~/.claude/CLAUDE.md with exactly this content:

# Global Preferences

Always respond in British English. Use "colour" not "color",
"organise" not "organize", "realise" not "realize".
When writing prose, prefer shorter sentences.
```

**Step 2:** Create a project-level CLAUDE.md with a project rule.

This file applies only when Claude Code is open in this directory.
Paste this prompt:

```
Create a CLAUDE.md in the current directory (not ~/.claude/) with exactly this content:

# Project Rules

Language: TypeScript only. No JavaScript files.
Indentation: 2 spaces. No tabs.
Imports: named imports preferred over default imports.
```

**Step 3:** Create a subdirectory CLAUDE.md with test-specific rules.

```bash
mkdir -p tests
```

Then paste:

```
Create a file at tests/CLAUDE.md with exactly this content:

# Test Rules

Test framework: vitest only.
Pattern: describe/it blocks with descriptive names.
Assertions: use expect() with .toBe(), .toEqual(), or .toThrow().
No jest, no mocha, no chai.
```

**Step 4:** Ask Claude to create a function and a test, then observe.

Paste this prompt:

```
Write a TypeScript function called formatDate that takes a Date object
and returns a string in the format "DD Month YYYY" (e.g. "04 April 2025").

Then write a vitest test for it in tests/formatDate.test.ts.
```

Watch the output carefully. Claude should:
- Use TypeScript (project rule)
- Use 2-space indentation (project rule)
- Use named imports (project rule)
- Use vitest with describe/it (test rule)
- Write in British English where prose appears (global rule)

---

## Expected Output

After completing all four steps, you should see:

- A `formatDate.ts` file using TypeScript, 2-space indentation, named imports
- A `tests/formatDate.test.ts` file using vitest, describe/it pattern
- Any comments or prose Claude writes use British English spellings
- Claude did not ask which framework to use or what indentation to apply

**How you know hierarchy worked:**
All three levels applied at once. The test file followed both the project
rules (TypeScript, 2-space) AND the test-specific rules (vitest, describe/it).
The global preference (British English) applied throughout.

---

## What You Learned

- **Global scope:** `~/.claude/CLAUDE.md` applies to every project
- **Project scope:** `./CLAUDE.md` applies only in the current directory
- **Subdirectory scope:** `tests/CLAUDE.md` applies only when working in `tests/`
- **More specific overrides broader:** If a test-specific rule conflicts with
  a project rule, the test-specific rule wins inside `tests/`
- **All levels apply simultaneously:** Claude does not choose one level.
  It reads all of them and follows all of them

---

## Clean Up

```bash
rm -f CLAUDE.md formatDate.ts tests/CLAUDE.md tests/formatDate.test.ts
rmdir tests 2>/dev/null || true
```

And if you backed up your global CLAUDE.md:

```bash
mv ~/.claude/CLAUDE.md.bak ~/.claude/CLAUDE.md
```

Or remove the test global file if you created a fresh one:

```bash
rm ~/.claude/CLAUDE.md
```

---

## Next

Ready to take a bad CLAUDE.md and make it effective? Move to
[Exercise 03: Audit and Improve](./03-audit-and-improve.md).