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 Identify unwanted behavior Determine which tool is involved (Bash, Edit, etc.) Choose event type (bash, file, stop, etc.) Write regex pattern Create .claude/hookify.{name}.local.md file in project root Test immediately - rules are read dynamically on next tool use Refining a Rule Edit the .local.md file Adjust pattern or message 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