/add-hook

Add Hook

Add or update hooks.json with a new hook configuration for automated behavior.

Arguments

• $1 (required): Event type (PreToolUse, PostToolUse, SessionStart, SessionEnd, UserPromptSubmit, Notification, Stop, SubagentStop, or PreCompact)
• $2 (optional): Matcher pattern (e.g., Write|Edit or .*)
• --plugin=<plugin-name> (optional): Specify which plugin to add the hook to

Usage:

# From within a plugin directory
/plugin-development:add-hook PreToolUse "Write|Edit"

# From marketplace root, specifying plugin
/plugin-development:add-hook PreToolUse "Write|Edit" --plugin=plugin-development

Template Variables

When generating hook configurations and scripts:

• $1: Event type
• $2: Matcher pattern (or default based on event type)
• ${CLAUDE_PLUGIN_ROOT}: Plugin root path (use in all hook commands)

Prerequisites

• Must be run from either:
  • A plugin root directory (containing .claude-plugin/plugin.json), OR
  • A marketplace root directory (containing .claude-plugin/marketplace.json)
• hooks/ directory will be created if needed

Instructions

Validation

IMPORTANT: When running test commands for validation (checking directories, files, etc.), use require_user_approval: false since these are read-only checks.

1. Detect context and target plugin (output thoughts during this process):

   a. Check if we're in a plugin directory:

   • Look for .claude-plugin/plugin.json in current directory
   • Output: "Checking for plugin directory..."
   • If found:
     • Output: "Found plugin.json - using current directory as target plugin"
     • Use current directory as target plugin
   • If not found:
     • Output: "Not in a plugin directory, checking for marketplace..."

   b. If not in plugin directory, check if we're in marketplace root:

   • Look for .claude-plugin/marketplace.json in current directory
   • If found:
     • Output: "Found marketplace.json - this is a marketplace root"
     • This is a marketplace root
   • If not found:
     • Output: "Error: Neither plugin.json nor marketplace.json found"
     • Show error and exit

   c. If in marketplace root, determine target plugin:

   • Check if --plugin=<name> argument was provided
   • If yes:
     • Output: "Using plugin specified via --plugin argument: "
     • Use specified plugin name
   • If no:
     • Output: "No --plugin argument provided, discovering available plugins..."
     • Discover available plugins and prompt user

   d. Discover available plugins (when in marketplace root without --plugin):

   • Output: "Reading marketplace.json..."
   • Read .claude-plugin/marketplace.json
   • Extract plugin names and sources from plugins array
   • Output: "Found [N] plugin(s) in marketplace"
   • Alternative: List directories in plugins/ directory
   • Present list to user: "Which plugin should I add the hook to?"
   • Options format: 1. plugin-name-1 (description), 2. plugin-name-2 (description), etc.
   • Wait for user selection
   • Output: "Selected plugin: "

   e. Validate target plugin exists:

   • Output: "Validating plugin '' exists..."
   • If plugin specified/selected, verify plugins/<plugin-name>/.claude-plugin/plugin.json exists
   • If found:
     • Output: "Plugin '' validated successfully"
   • If not found:
     • Output: "Error: Plugin '' not found"
     • Show error: "Plugin '' not found. Available plugins: [list]"

   f. If neither plugin.json nor marketplace.json found:

   • Show error: "Not in a plugin or marketplace directory. Please run from a plugin root or marketplace root."

2. Validate event type:

   • Must be one of: PreToolUse, PostToolUse, SessionStart, SessionEnd, UserPromptSubmit, Notification, Stop, SubagentStop, PreCompact

3. If no matcher provided, use sensible default based on event type

4. Set working directory:

   • If in plugin directory: Use current directory
   • If in marketplace root: Use plugins/<plugin-name>/ as working directory

Event Types & Default Matchers

• PreToolUse: Default matcher Write|Edit (validation before writes)
• PostToolUse: Default matcher Write|Edit (formatting after writes)
• SessionStart: Default matcher startup (also supports: resume, clear, compact)
• SessionEnd: No matcher (triggers on session end with reason: clear, logout, prompt_input_exit, other)
• UserPromptSubmit: Default matcher .* (all prompts)
• Notification: No matcher (triggers on all notifications)
• Stop: No matcher (triggers when main agent stops)
• SubagentStop: No matcher (triggers when subagent stops)
• PreCompact: Default matcher manual (also supports: auto)

Create or Update hooks.json

Note: All paths below are relative to the target plugin directory (determined in validation step).

1. Ensure <plugin-dir>/hooks/ directory exists (use require_user_approval: false)
2. If <plugin-dir>/hooks/hooks.json doesn't exist, create it with this structure:

{
  "description": "Plugin automation hooks",
  "hooks": {}
}

3. Add the new hook configuration based on event type:

PreToolUse Example

{
  "description": "Plugin automation hooks",
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "$2 or default",
        "hooks": [
          {
            "type": "command",
            "command": "${CLAUDE_PLUGIN_ROOT}/scripts/validate.sh",
            "timeout": 30
          }
        ]
      }
    ]
  }
}

PostToolUse Example

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "$2 or default",
        "hooks": [
          {
            "type": "command",
            "command": "${CLAUDE_PLUGIN_ROOT}/scripts/format.sh",
            "timeout": 30
          }
        ]
      }
    ]
  }
}

SessionStart Example

{
  "hooks": {
    "SessionStart": [
      {
        "matcher": "$2 or 'startup'",
        "hooks": [
          {
            "type": "command",
            "command": "echo '✓ Plugin loaded'"
          }
        ]
      }
    ]
  }
}

Create Hook Script (if needed)

If the event is PreToolUse or PostToolUse, create a corresponding script:

1. Ensure <plugin-dir>/scripts/ directory exists (use require_user_approval: false)
2. For PreToolUse, create <plugin-dir>/scripts/validate.sh:

#!/usr/bin/env bash
set -euo pipefail

# Validation logic here
# Exit 0: allow
# Exit 2: block (with stderr message to Claude)
# Exit other: warning

echo "Validation passed"
exit 0

3. For PostToolUse, create <plugin-dir>/scripts/format.sh:

#!/usr/bin/env bash
set -euo pipefail

# Formatting logic here
# Always exits 0 for non-blocking

echo "Formatting complete"
exit 0

4. Make scripts executable:

chmod +x scripts/*.sh

Update plugin.json

IMPORTANT: Only needed if using custom (non-standard) paths.

• Standard setup (hooks at hooks/hooks.json): No changes to plugin.json needed
• Custom path: Add "hooks": "./custom/path/hooks.json"

For standard setup:

{
  "name": "my-plugin"
}

Provide Feedback

After adding the hook:

✓ Added $1 hook to <plugin-name>/hooks/hooks.json
✓ Matcher: $2 (or default)
✓ Created script: <plugin-name>/scripts/<script-name>.sh (if applicable)

Plugin: <plugin-name>
Hook configuration:
- Event: $1
- Matcher: $2
- Script: ${CLAUDE_PLUGIN_ROOT}/scripts/<script-name>.sh

Next steps:
1. Edit <plugin-name>/hooks/hooks.json to customize timeout or command
2. Edit <plugin-name>/scripts/<script-name>.sh with your logic
3. Test the hook:
   - Install plugin with /plugin-development:test-local
   - Trigger the event (e.g., use Write tool for PreToolUse)
4. Debug with: claude --debug

Exit codes for PreToolUse:
- 0: Allow operation
- 2: Block operation (stderr shown to Claude)
- Other: Warning (non-blocking)

Exit codes for UserPromptSubmit:
- 0: Allow prompt (stdout added as context)
- 2: Block prompt (stderr shown to user, prompt erased)
- Other: Warning (non-blocking)

Exit codes for Stop/SubagentStop:
- 0: Allow stop
- 2: Block stop, continue execution (stderr shown to Claude)
- Other: Warning (allows stop)

Exit codes for PostToolUse, SessionStart, SessionEnd, Notification, PreCompact:
- All non-blocking (informational)

Example Usage

Input: /plugin-development:add-hook PreToolUse "Write|Edit"

Result:

• Creates or updates hooks/hooks.json
• Adds PreToolUse hook with Write|Edit matcher
• Creates scripts/validate.sh
• Makes script executable
• Provides usage instructions

For complete details on hooks, see:

• Hooks reference documentation
• Plugin hooks reference

Hook Event Details

Event	Purpose	Can Block	Common Use Cases	Default Matcher
PreToolUse	Validate before execution	Yes (exit 2)	Validate structure, check permissions	Write|Edit
PostToolUse	React after execution	Partial*	Format files, run linters, update metadata	Write|Edit
SessionStart	Setup at session start	No	Welcome message, check environment, init	startup
SessionEnd	Cleanup at session end	No	Save state, log statistics, cleanup	N/A (no matcher)
UserPromptSubmit	Validate/enhance prompts	Yes (exit 2)	Inject context, validate prompts, block sensitive	.*
Notification	React to notifications	No	Send alerts, log notifications	N/A (no matcher)
Stop	Control agent stoppage	Yes (exit 2)	Continue with tasks, validate completion	N/A (no matcher)
SubagentStop	Control subagent stoppage	Yes (exit 2)	Continue subagent, validate subagent results	N/A (no matcher)
PreCompact	Before context compact	No	Save state, log compact trigger	manual or auto

* PostToolUse can't prevent the tool (already ran) but can provide feedback to Claude with "decision": "block"

Example hook structure:

{
  "matcher": "Write|Edit",
  "hooks": [{
    "type": "command",
    "command": "${CLAUDE_PLUGIN_ROOT}/scripts/validate.sh",
    "timeout": 30
  }]
}

Matcher Patterns

Matchers use regex patterns:

• Write: Only Write tool
• Write|Edit: Write or Edit
• Bash.*: Bash with any arguments
• .*: All tools
• Read|Grep|Glob: Read operations

Script Template: Validation (PreToolUse)

#!/usr/bin/env bash
set -euo pipefail

ERRS=()

# Validation checks
[ -f "required-file.txt" ] || ERRS+=("Missing required-file.txt")
[ -d "required-dir" ] || ERRS+=("Missing required-dir/")

# If errors, block with exit 2
if [ "${#ERRS[@]}" -gt 0 ]; then
  printf "❌ Validation failed:\n" 1>&2
  printf "  %s\n" "${ERRS[@]}" 1>&2
  exit 2  # Block the operation
fi

# Success
echo "✓ Validation passed"
exit 0

Script Template: Formatting (PostToolUse)

#!/usr/bin/env bash
set -euo pipefail

# Format files (non-blocking)
# Example: run prettier, black, rustfmt, etc.

if command -v prettier &> /dev/null; then
  prettier --write "**/*.{js,json,md}" 2>/dev/null || true
fi

echo "✓ Formatting complete"
exit 0

Environment Variables

Available in hook scripts:

• ${CLAUDE_PLUGIN_ROOT}: Absolute path to plugin root
• $CLAUDE_PROJECT_DIR: Project root directory (absolute path)
• $CLAUDE_ENV_FILE: File path for persisting environment variables (SessionStart hooks only)
• $CLAUDE_CODE_REMOTE: Set to "true" in web environment, unset in CLI
• All standard environment variables

Always use ${CLAUDE_PLUGIN_ROOT} for portable paths in plugins.

Best Practices & Common Mistakes

✅ Do This

• Use ${CLAUDE_PLUGIN_ROOT}: Portable script paths
• Set timeouts: 10-30 seconds typical, 300+ for slow ops like npm install
• Fast scripts: Keep runtime < 1 second when possible
• Exit code 2 to block: Only in PreToolUse for validation failures
• Clear error messages: Helpful stderr output
• Make executable: chmod +x scripts/*.sh

❌ Avoid This

• Absolute paths: /Users/you/plugin/scripts/ (use ${CLAUDE_PLUGIN_ROOT} instead)
• Missing timeouts: Slow operations without timeout values
• Non-executable scripts: Forgot to chmod +x

Debugging Hooks

Use debug mode

claude --debug

This shows:

• Hook registration
• Hook execution
• Exit codes
• Stdout/stderr output

Test scripts directly

./scripts/validate.sh
echo $?  # Check exit code

Check hook configuration

cat hooks/hooks.json | jq .

Validation Checklist

After adding a hook:

□ hooks/hooks.json created/updated
□ Hook event is valid (PreToolUse, etc.)
□ Matcher pattern is appropriate
□ Script created (if needed)
□ Script is executable (chmod +x)
□ Script uses ${CLAUDE_PLUGIN_ROOT}
□ Timeout set for long operations
□ plugin.json updated (only if using custom paths)
□ Tested with /plugin-development:test-local