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Writing Hookify Rules

AnthropicOfficialPublished by Anthropic

  • Skill
  • Guidelines
  • Automation and integrations
  • Apache-2.0
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From the author

This skill should be used when the user asks to "create a hookify rule", "write a hook rule", "configure hookify", "add a hookify rule", or needs guidance on hookify rule syntax and patterns.
— the description by Anthropic

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

Hookify allows you to define custom rules that monitor an agent's interactions with bash commands, file edits, stop events, and user prompts. By creating markdown files with YAML frontmatter in the .claude directory, you can trigger warnings or blocks based on specific patterns, helping to enforce best practices, prevent dangerous operations, or provide context-aware reminders during a session.

What it does

  • Defines patterns to watch for in bash commands, file edits, and user prompts.
  • Supports simple regex-based matching or complex multi-condition logic.
  • Allows for custom warning messages to be displayed when a rule is triggered.
  • Enables blocking of specific operations to prevent errors or security risks.
  • Provides a mechanism for completion checklists before an agent stops.
  • Uses dynamic loading so rules take effect immediately upon file creation or update.

When to use it

  • When you need to prevent the execution of dangerous bash commands like rm -rf.
  • When you want to warn developers about committing debug code like console.log.
  • When you need to enforce project-specific workflows or checklists before stopping.
  • When you want to restrict edits to sensitive files like .env or configuration files.
  • When you need to provide guidance or reminders based on specific user prompts.

Advantages

  • Highly flexible configuration using standard markdown and YAML.
  • Rules are stored locally within the project for easy version control.
  • Supports both simple regex and advanced multi-condition logic.
  • Immediate feedback loop without needing to restart the agent.
  • Non-destructive; rules can be toggled via the enabled flag.

Usage examples

“Create a hookify rule to warn me whenever I try to use the rm -rf command.”
The agent will generate a .claude/hookify.warn-rm-rf.local.md file with the appropriate bash event and regex pattern to trigger a warning.
“How do I block edits to my .env file that include an API_KEY?”
The agent will provide a multi-condition rule template that checks both the file_path and the new_text fields to block the edit.

Install

  1. Download the skill as a ZIP:

    https://mp-staging.autogineer.com/agent-skills/anthropics/writing-hookify-rules/download
  2. Unzip it into the cross-client skills folder of your project:

    mkdir -p .agents/skills && unzip writing-hookify-rules.zip -d .agents/skills

Documentation by Anthropic

Writing Hookify Rules

Overview

Hookify rules are markdown files with YAML frontmatter that define patterns to watch for and messages to show when those patterns match. Rules are stored in .claude/hookify.{rule-name}.local.md files.

Rule File Format

Basic Structure
---
name: rule-identifier
enabled: true
event: bash|file|stop|prompt|all
pattern: regex-pattern-here
---

Message to show Claude when this rule triggers.
Can include markdown formatting, warnings, suggestions, etc.
Frontmatter Fields

name (required): Unique identifier for the rule

  • Use kebab-case: warn-dangerous-rm, block-console-log

  • Be descriptive and action-oriented

  • Start with verb: warn, prevent, block, require, check

enabled (required): Boolean to activate/deactivate

  • true: Rule is active

  • false: Rule is disabled (won't trigger)

  • Can toggle without deleting rule

event (required): Which hook event to trigger on

  • bash: Bash tool commands

  • file: Edit, Write, MultiEdit tools

  • stop: When agent wants to stop

  • prompt: When user submits a prompt

  • all: All events

action (optional): What to do when rule matches

  • warn: Show message but allow operation (default)

  • block: Prevent operation (PreToolUse) or stop session (Stop events)

  • If omitted, defaults to warn

pattern (simple format): Regex pattern to match

  • Used for simple single-condition rules

  • Matches against command (bash) or new_text (file)

  • Python regex syntax

Example:

event: bash
pattern: rm\s+-rf
Advanced Format (Multiple Conditions)

For complex rules with multiple conditions:

---
name: warn-env-file-edits
enabled: true
event: file
conditions:
  - field: file_path
    operator: regex_match
    pattern: \.env$
  - field: new_text
    operator: contains
    pattern: API_KEY
---

You're adding an API key to a .env file. Ensure this file is in .gitignore!

Condition fields:

  • field: Which field to check

    • For bash: command

    • For file: file_path, new_text, old_text, content

  • operator: How to match

    • regex_match: Regex pattern matching

    • contains: Substring check

    • equals: Exact match

    • not_contains: Substring must NOT be present

    • starts_with: Prefix check

    • ends_with: Suffix check

  • pattern: Pattern or string to match

All conditions must match for rule to trigger.

Message Body

The markdown content after frontmatter is shown to Claude when the rule triggers.

Good messages:

  • Explain what was detected

  • Explain why it's problematic

  • Suggest alternatives or best practices

  • Use formatting for clarity (bold, lists, etc.)

Example:

⚠️ **Console.log detected!**

You're adding console.log to production code.

**Why this matters:**
- Debug logs shouldn't ship to production
- Console.log can expose sensitive data
- Impacts browser performance

**Alternatives:**
- Use a proper logging library
- Remove before committing
- Use conditional debug builds

Event Type Guide

bash Events

Match Bash command patterns:

---
event: bash
pattern: sudo\s+|rm\s+-rf|chmod\s+777
---

Dangerous command detected!

Common patterns:

  • Dangerous commands: rm\s+-rf, dd\s+if=, mkfs

  • Privilege escalation: sudo\s+, su\s+

  • Permission issues: chmod\s+777, chown\s+root

file Events

Match Edit/Write/MultiEdit operations:

---
event: file
pattern: console\.log\(|eval\(|innerHTML\s*=
---

Potentially problematic code pattern detected!

Match on different fields:

---
event: file
conditions:
  - field: file_path
    operator: regex_match
    pattern: \.tsx?$
  - field: new_text
    operator: regex_match
    pattern: console\.log\(
---

Console.log in TypeScript file!

Common patterns:

  • Debug code: console\.log\(, debugger, print\(

  • Security risks: eval\(, innerHTML\s*=, dangerouslySetInnerHTML

  • Sensitive files: \.env$, credentials, \.pem$

  • Generated files: node_modules/, dist/, build/

stop Events

Match when agent wants to stop (completion checks):

---
event: stop
pattern: .*
---

Before stopping, verify:
- [ ] Tests were run
- [ ] Build succeeded
- [ ] Documentation updated

Use for:

  • Reminders about required steps

  • Completion checklists

  • Process enforcement

prompt Events

Match user prompt content (advanced):

---
event: prompt
conditions:
  - field: user_prompt
    operator: contains
    pattern: deploy to production
---

Production deployment checklist:
- [ ] Tests passing?
- [ ] Reviewed by team?
- [ ] Monitoring ready?

Pattern Writing Tips

Regex Basics

Literal characters: Most characters match themselves

  • rm matches "rm"

  • console.log matches "console.log"

Special characters need escaping:

  • . (any char) → \. (literal dot)

  • ( ) → \( \) (literal parens)

  • [ ] → \[ \] (literal brackets)

Common metacharacters:

  • \s - whitespace (space, tab, newline)

  • \d - digit (0-9)

  • \w - word character (a-z, A-Z, 0-9, _)

  • . - any character

  • + - one or more

  • * - zero or more

  • ? - zero or one

  • | - OR

Examples:

rm\s+-rf         Matches: rm -rf, rm  -rf
console\.log\(   Matches: console.log(
(eval|exec)\(    Matches: eval( or exec(
chmod\s+777      Matches: chmod 777, chmod  777
API_KEY\s*=      Matches: API_KEY=, API_KEY =
Testing Patterns

Test regex patterns before using:

python3 -c "import re; print(re.search(r'your_pattern', 'test text'))"

Or use online regex testers (regex101.com with Python flavor).

Common Pitfalls

Too broad:

pattern: log    # Matches "log", "login", "dialog", "catalog"

Better: console\.log\(|logger\.

Too specific:

pattern: rm -rf /tmp  # Only matches exact path

Better: rm\s+-rf

Escaping issues:

  • YAML quoted strings: "pattern" requires double backslashes \\s

  • YAML unquoted: pattern: \s works as-is

  • Recommendation: Use unquoted patterns in YAML

File Organization

Location: All rules in .claude/ directory Naming: .claude/hookify.{descriptive-name}.local.md Gitignore: Add .claude/*.local.md to .gitignore

Good names:

  • hookify.dangerous-rm.local.md

  • hookify.console-log.local.md

  • hookify.require-tests.local.md

  • hookify.sensitive-files.local.md

Bad names:

  • hookify.rule1.local.md (not descriptive)

  • hookify.md (missing .local)

  • danger.local.md (missing hookify prefix)

Workflow

Creating a Rule
  1. Identify unwanted behavior

  2. Determine which tool is involved (Bash, Edit, etc.)

  3. Choose event type (bash, file, stop, etc.)

  4. Write regex pattern

  5. Create .claude/hookify.{name}.local.md file in project root

  6. Test immediately - rules are read dynamically on next tool use

Refining a Rule
  1. Edit the .local.md file

  2. Adjust pattern or message

  3. Test immediately - changes take effect on next tool use

Disabling a Rule

Temporary: Set enabled: false in frontmatter Permanent: Delete the .local.md file

Examples

See ${CLAUDE_PLUGIN_ROOT}/examples/ for complete examples:

  • dangerous-rm.local.md - Block dangerous rm commands

  • console-log-warning.local.md - Warn about console.log

  • sensitive-files-warning.local.md - Warn about editing .env files

Quick Reference

Minimum viable rule:

---
name: my-rule
enabled: true
event: bash
pattern: dangerous_command
---

Warning message here

Rule with conditions:

---
name: my-rule
enabled: true
event: file
conditions:
  - field: file_path
    operator: regex_match
    pattern: \.ts$
  - field: new_text
    operator: contains
    pattern: any
---

Warning message

Event types:

  • bash - Bash commands

  • file - File edits

  • stop - Completion checks

  • prompt - User input

  • all - All events

Field options:

  • Bash: command

  • File: file_path, new_text, old_text, content

  • Prompt: user_prompt

Operators:

  • regex_match, contains, equals, not_contains, starts_with, ends_with

Files

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Requirements and compatibility

Written for: Claude Code, Claude apps

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

Needs: Names Claude Code tools, Needs an API key, Needs Python

Security

No issues found by our static scan· No issues found

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Attribution and licence

Published by
Anthropic
Publisher
Anthropic (Official)
Source
anthropics/claude-plugins-official · plugins/hookify/skills/writing-rules · commit 0412be7
Licence
Apache License 2.0 (redistribution allowed)
  • LICENSE (added by AutoGineer from plugins/hookify/LICENSE)
  • ATTRIBUTION.md (written by AutoGineer)
Synced

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