Lesson 5.3 — Harnesses: CLAUDE.md, Permissions, Hooks

Introduction to AI · Module 5: AI Agents · About 75 min · Windows PC, PowerShell 5, Claude Code (Max)

Goal: control how your Folder Tidy agent behaves: standing instructions, a rule it can't break (no deleting), and a one-word command /tidy.

Before you start

• cd $HOME\agent-night (your 5.1 folder with messy, check.ps1 and CLAUDE.md)

Step 1 · Reset the mess (⏱ 0:00–0:05)

dir messy -Recurse -File | Move-Item -Destination messy -Force
Remove-Item messy\Documents, messy\Images, messy\Spreadsheets -Recurse -ErrorAction SilentlyContinue
Remove-Item messy\REPORT.md -ErrorAction SilentlyContinue
.\check.ps1

You should see FAIL.

• Reset done

Step 2 · Upgrade CLAUDE.md (⏱ 0:05–0:15)

Open it:

notepad CLAUDE.md

Add these lines at the bottom, then save:

Style:
- Before moving anything, print a short plan (max 5 lines).
- After PASS, reply with one line: "Tidied N files. PASS."

• CLAUDE.md updated

Step 3 · Add a hard rule: no deleting (⏱ 0:15–0:30)

CLAUDE.md is advice. Permission rules are enforced by the harness, whatever the model wants. Paste the whole block:

mkdir .claude -Force | Out-Null
$json = @'
{
  "permissions": {
    "allow": ["Read", "Glob", "Edit", "Write"],
    "deny": [
      "Bash(rm:*)", "Bash(del:*)",
      "PowerShell(Remove-Item:*)", "PowerShell(rm:*)", "PowerShell(del:*)"
    ]
  }
}
'@
[IO.File]::WriteAllText("$HOME\agent-night\.claude\settings.json", $json)
Get-Content .claude\settings.json

Inside Claude, /permissions shows the active rules.

• settings.json created

Step 4 · Test the rule (⏱ 0:30–0:40)

claude

Type:

Delete the file messy\a-receipt.pdf

You should see Claude get blocked or refuse (a "denied" message or similar). If it asks permission instead, choose No and note that the rule didn't match the command it tried.

Then **type /exit and press Enter. Wait until you see PS C:\...> before the next command.** Then check the file is still there:

Test-Path messy\a-receipt.pdf

You should see True.

• Delete was blocked; file still there

Step 5 · Make a /tidy command (⏱ 0:40–0:55)

mkdir .claude\commands -Force | Out-Null
$cmd = @'
Tidy the messy folder following CLAUDE.md. Run .\check.ps1 at the end and report the result.
'@
[IO.File]::WriteAllText("$HOME\agent-night\.claude\commands\tidy.md", $cmd)
claude

In Claude, type:

/tidy

You should see a short plan, the moves, then Tidied 12 files. PASS.

• /tidy worked end to end

Step 6 · Peek at hooks (⏱ 0:55–1:10, optional)

Hooks are scripts the harness runs automatically, e.g. after every file edit. In Claude, type /hooks to see the menu. Just look for now: you'll build one in Module 7.

Write one line: a hook I'd want is .

Then **type /exit and press Enter. Wait until you see PS C:\...> before the next command.**

✅ Pass check

• /tidy runs the whole job and ends with PASS
• Asking to delete a file was blocked, and the file still exists
• Told Skills Coach so 5.3 gets marked done

Troubleshooting