tddyco-guardian

Guardian Plugin for Claude Code

An LLM-based PreToolUse hook that auto-approves read-only Bash commands and defers everything else to the normal user approval prompt.

Tired of manually approving ls, cat, python analyze.py, and git log? This plugin invokes claude -p as a security reviewer to inspect each Bash command (including reading script files the agent may have written) and auto-approves when it's confident the operation is safe.

What gets auto-approved

• Read-only commands: cat, ls, grep, find, jq, diff, wc, head, tail, etc.
• Git read-only: git log, git diff, git status, git show, git blame, etc.
• GitHub CLI read-only: gh pr view, gh pr list, gh issue list, gh api (GET only)
• System info: du, df, ps, uname, whoami
• Writes within CWD, /tmp, or Claude memory: mkdir, touch, cp, mv, rm, output redirects — anything that stays inside the project directory, /tmp, or ~/.claude/projects/*/memory/
• Scripts: Python/Node/Bash scripts in the project directory — the guardian reads the script contents to verify they're safe before approving

What gets deferred to the user

Everything else, including:

• Mutating git operations (git commit, git push)
• Package installation (npm install, pip install)
• Writes outside CWD, /tmp, and ~/.claude/projects/*/memory/
• Downloads (curl, wget)
• gh api with mutating HTTP methods
• sudo, chmod/chown on system paths

There is no "deny" category — the user always has the final say via the normal approval prompt.

Install

For teammates

/plugin marketplace add tddyco/guardian
/plugin install guardian@tddyco-guardian

Development / testing

claude --plugin-dir /path/to/claude-guardian/claude

Verify

Run /hooks inside Claude Code to confirm the PreToolUse hook is loaded ([command] type).

Customization

The policy lives in claude/policy.md and is read at runtime by the hook script. No build step needed.

To customize:

1. Fork this repo
2. Edit claude/policy.md with your changes
3. To change the model, edit the --model flag in claude/hooks/guardian.sh
4. To change the timeout, edit claude/hooks/hooks.json

How it works

The plugin registers a PreToolUse command hook on the Bash tool. When a Bash command needs approval:

1. guardian.sh reads the hook input JSON from stdin
2. It invokes claude -p --model sonnet with the policy as system prompt and the command details as user input
3. --json-schema enforces {"ok": boolean, "reason": string} output
4. --tools "Read" lets the reviewer inspect script files but not write or execute anything
5. --settings '{"disableAllHooks":true}' prevents recursive hook calls
6. If ok: true → auto-approve. Otherwise → show normal approval prompt
7. Commands already covered by your allow-rules in settings.json bypass the hook entirely

Debugging

• Ctrl+O in Claude Code toggles verbose mode — shows hook stdout/stderr inline
• --debug flag shows full hook execution details
• /hooks menu to verify the hook is loaded and check its source

Known limitations

• Fail-open on errors: if the guardian times out or crashes, the command falls through to the normal approval prompt. This is safe — the worst case is you see the prompt you'd normally see anyway.
• No conversation context: the guardian only sees the current command and can read files, but doesn't have the full conversation history.
• Allow-rules take precedence: commands already whitelisted in your settings.json bypass the guardian entirely.

Cost

The hook invokes claude -p (Sonnet) on every non-whitelisted Bash command. For typical data analysis workflows this is a small overhead, but it adds up with many commands. Consider whitelisting your most frequent safe commands in settings.json to bypass the hook entirely.

Comparison to alternatives

Guardian was inspired by Codex's experimental Guardian system, which uses an LLM sub-agent to review tool calls for safety. I wanted something similar for Claude Code — but with a different philosophy.

Codex Guardian and Claude Code's auto mode are primarily safety tools: they block destructive or malicious actions while letting normal work flow through. Guardian is much more conservative, while still being much more permissive than a typical sandbox. It auto-approves only operations with an extremely limited blast radius (reads + writes to CWD/tmp), and defers everything else to the user. This includes actions that are perfectly safe but externally visible, like posting a GitHub comment, pushing a branch, or installing a package. The goal isn't just to prevent damage, it's to prevent the AI from taking any irreversible or externally-visible action without explicit human review.