Hook Creator Skill | Agent Skills

Hook Creator

Create Claude Code hooks that execute shell commands at specific lifecycle events.

Hook Creation Workflow

Identify the use case - Determine what the hook should accomplish
Select the appropriate event - Choose from available hook events (see references/hook-events.md)
Design the hook command - Write shell command that processes JSON input from stdin
Configure the matcher - Set tool/event filter (use * for all, or specific tool names like Bash, Edit|Write)
Choose storage location - User settings (~/.claude/settings.json) or project (.claude/settings.json)
Test the hook - Verify behavior with a simple test case

Hook Configuration Structure

{
  "hooks": {
    "<EventName>": [
      {
        "matcher": "<ToolPattern>",
        "hooks": [
          {
            "type": "command",
            "command": "<shell-command>"
          }
        ]
      }
    ]
  }
}

Common Patterns

Reading Input Data

Hooks receive JSON via stdin. Use jq to extract fields:

# Extract tool input field
jq -r '.tool_input.file_path'

# Extract with fallback
jq -r '.tool_input.description // "No description"'

# Conditional processing
jq -r 'if .tool_input.file_path then .tool_input.file_path else empty end'

Exit Codes for PreToolUse

0 - Allow the tool to proceed
2 - Block the tool and provide feedback to Claude

Matcher Patterns

* - Match all tools
Bash - Match only Bash tool
Edit|Write - Match Edit or Write tools
Read - Match Read tool

Quick Examples

Log all bash commands:

jq -r '"\(.tool_input.command)"' >> ~/.claude/bash-log.txt

Auto-format TypeScript after edit:

jq -r '.tool_input.file_path' | { read f; [[ "$f" == *.ts ]] && npx prettier --write "$f"; }

Block edits to .env files:

python3 -c "import json,sys; p=json.load(sys.stdin).get('tool_input',{}).get('file_path',''); sys.exit(2 if '.env' in p else 0)"

Resources

Hook Events Reference: See references/hook-events.md for detailed event documentation with input/output schemas
Example Configurations: See references/examples.md for complete, tested hook configurations

Agent Skills: Hook Creator

Install this agent skill to your local

Skill Files