Hooks Manager Skill | Agent Skills

Hooks Manager

Overview

hooks-manager enables sophisticated workflow automation through Claude Code's hooks system (released June 2025).

Purpose: Create event-driven automation for code formatting, security gates, observability, and validation

Pattern: Task-based (8 operations, one per hook event + management)

Key Innovation: Hooks transform Claude Code from interactive to automated - reducing manual work by up to 92%

Hook Events Available (8):

UserPromptSubmit - Before Claude sees prompts
PreToolUse - Before tool execution
PostToolUse - After tool execution
PermissionRequest - When permissions requested
Notification - Important events
SessionStart - Session initialization
SessionEnd - Session cleanup
Stop - Conversation termination

When to Use

Use hooks-manager when:

Auto-formatting code (PostToolUse after Write/Edit)
Security gates (PreToolUse to block dangerous operations)
Observability integration (send telemetry on all tool calls)
Validation enforcement (block invalid operations)
Workflow automation (trigger actions on events)
Team standardization (enforce coding standards)

Production Impact: Companies report 92% reduction in style review time with PostToolUse formatting hooks

Prerequisites

Required

Claude Code (hooks support added June 2025)
Basic understanding of event-driven programming

Hook Operations

Operation 1: Create Formatting Hook (PostToolUse)

Purpose: Auto-format code after AI writes/edits files

Use Case: Enforce coding standards without manual intervention

Process:

Choose Formatter:

# JavaScript/TypeScript
npm install --save-dev prettier

# Python
pip install black

# Multi-language
npm install --save-dev prettier @prettier/plugin-python

Create Hook Configuration:

{
  "event": "PostToolUse",
  "tools": ["Write", "Edit"],
  "description": "Auto-format code after Claude writes/edits files",
  "handler": {
    "command": "npx prettier --write \"$FILE\"",
    "timeout": 5000
  },
  "filters": {
    "filePatterns": ["**/*.{ts,tsx,js,jsx,py}"],
    "excludePatterns": ["node_modules/**", "*.min.js"]
  }
}

Install Hook:

# Global hook (all projects)
mkdir -p ~/.claude/hooks
echo '[above-json]' > ~/.claude/hooks/auto-format.json

# Project-specific
mkdir -p .claude/hooks
echo '[above-json]' > .claude/hooks/auto-format.json

Test Hook:

# Have Claude write unformatted code
# Hook should auto-format after Write/Edit
# Verify formatted correctly

Outputs:

Hook configuration file
Auto-formatting on all code changes
92% reduction in style review time

Validation:

[ ] Hook file created
[ ] Formatter configured correctly
[ ] File patterns appropriate
[ ] Tested with Claude Code
[ ] Formatting works automatically

Time Estimate: 30-45 minutes

Operation 2: Create Security Hook (PreToolUse)

Purpose: Block dangerous operations before execution

Use Case: Prevent accidental production file modifications, destructive commands

Process:

Define Security Rules:

{
  "event": "PreToolUse",
  "tools": ["Write", "Edit", "Bash"],
  "description": "Block dangerous operations",
  "handler": {
    "command": ".claude/hooks/security-check.sh \"$TOOL\" \"$FILE\" \"$COMMAND\""
  },
  "structuredOutput": true
}

Create Security Check Script:

#!/bin/bash
# .claude/hooks/security-check.sh

TOOL=$1
FILE=$2
COMMAND=$3

# Block production file modifications
if [[ "$FILE" == "/etc/"* ]] || [[ "$FILE" == "/usr/"* ]]; then
  echo '{"continue": false, "stopReason": "Cannot modify system files", "suppressOutput": true}'
  exit 1
fi

# Block destructive commands
if [[ "$COMMAND" =~ rm\ -rf\ / ]] || [[ "$COMMAND" =~ dd\ if ]]; then
  echo '{"continue": false, "stopReason": "Destructive command blocked", "suppressOutput": true}'
  exit 1
fi

# Block curl/wget (security risk)
if [[ "$COMMAND" =~ curl|wget ]]; then
  echo '{"continue": false, "stopReason": "Network commands disabled", "suppressOutput": false}'
  exit 1
fi

# Allow operation
echo '{"continue": true}'
exit 0

Install Security Hook:

chmod +x .claude/hooks/security-check.sh
# Hook JSON already configured in step 1

Outputs:

Security hook blocking dangerous operations
Protection against accidental damage
Audit trail of blocked operations

Validation:

[ ] Hook blocks system file modifications
[ ] Hook blocks destructive commands
[ ] Hook allows safe operations
[ ] Structured JSON output correct

Time Estimate: 45-60 minutes

Operation 3: Create Observability Hook (Notification)

Purpose: Send telemetry to observability platform on important events

Use Case: Track AI agent decisions, tool usage, errors

Process:

Create Telemetry Hook:

{
  "event": "Notification",
  "description": "Send telemetry to observability platform",
  "handler": {
    "command": ".claude/hooks/send-telemetry.sh \"$EVENT_TYPE\" \"$MESSAGE\""
  }
}

Create Telemetry Script:

#!/bin/bash
# .claude/hooks/send-telemetry.sh

EVENT_TYPE=$1
MESSAGE=$2

# Send to observability platform (example: Victoria Metrics)
curl -X POST http://localhost:8428/api/v1/write \
  -d "claude_event{type=\"$EVENT_TYPE\"} 1" \
  -d "claude_message{event=\"$EVENT_TYPE\",msg=\"$MESSAGE\"} 1"

# Or log to file
echo "$(date -Iseconds) | $EVENT_TYPE | $MESSAGE" >> .claude/telemetry.log

# Or send to webhook
# curl -X POST https://your-webhook.com/telemetry \
#   -H "Content-Type: application/json" \
#   -d "{\"event\": \"$EVENT_TYPE\", \"message\": \"$MESSAGE\"}"

Test Telemetry:

# Trigger notification in Claude Code
# Check telemetry.log or observability platform
cat .claude/telemetry.log

Outputs:

Telemetry hook sending data
Observability integration
Decision tracking

Validation:

[ ] Hook configured
[ ] Telemetry script working
[ ] Data reaches destination
[ ] No performance impact

Time Estimate: 30-45 minutes

Operation 4: Create Validation Hook (PreToolUse)

Purpose: Validate inputs before tool execution

Use Case: Ensure files exist, validate JSON, check permissions

Process:

Create Validation Hook:

{
  "event": "PreToolUse",
  "tools": ["Write"],
  "description": "Validate JSON before writing",
  "handler": {
    "command": ".claude/hooks/validate-json.sh \"$FILE\" \"$CONTENT\""
  },
  "structuredOutput": true
}

Create Validation Script:

#!/bin/bash
# .claude/hooks/validate-json.sh

FILE=$1
CONTENT=$2

# Only validate .json files
if [[ "$FILE" != *.json ]]; then
  echo '{"continue": true}'
  exit 0
fi

# Validate JSON syntax
if echo "$CONTENT" | jq empty 2>/dev/null; then
  echo '{"continue": true}'
  exit 0
else
  echo '{"continue": false, "stopReason": "Invalid JSON syntax", "suppressOutput": false}'
  exit 1
fi

Outputs:

Validation hook preventing invalid writes
JSON syntax enforcement
Error prevention

Validation:

[ ] Hook validates JSON files
[ ] Hook allows non-JSON files
[ ] Invalid JSON blocked
[ ] Valid JSON allowed

Time Estimate: 20-30 minutes

Operation 5: Create MCP Tool Hook (PreToolUse)

Purpose: Control MCP tool access granularly

Use Case: Block specific MCP servers or tools

Process:

MCP Tool Targeting:

{
  "event": "PreToolUse",
  "tools": ["mcp__filesystem__*"],
  "description": "Block all filesystem MCP operations",
  "handler": {
    "command": "echo '{\"continue\": false, \"stopReason\": \"Filesystem MCP disabled\"}'"
  },
  "structuredOutput": true
}

Selective MCP Control:

{
  "event": "PreToolUse",
  "tools": ["mcp__github__delete_repository"],
  "description": "Block dangerous GitHub operations",
  "handler": {
    "command": "echo '{\"continue\": false, \"stopReason\": \"Repository deletion disabled\"}'"
  },
  "structuredOutput": true
}

Outputs:

Fine-grained MCP control
Security for MCP operations
Prevent accidental damage

Validation:

[ ] MCP tools blocked correctly
[ ] Tool targeting works (mcp__server__tool pattern)
[ ] Safe operations allowed

Time Estimate: 20-30 minutes

Operation 6: Create Comprehensive Hook (SessionStart)

Purpose: Initialize environment on session start

Use Case: Load context, set variables, validate environment

Process:

Session Start Hook:

{
  "event": "SessionStart",
  "description": "Initialize session with context and validation",
  "handler": {
    "command": ".claude/hooks/session-init.sh"
  }
}

Initialization Script:

#!/bin/bash
# .claude/hooks/session-init.sh

echo "🚀 Claude Code Session Starting..."

# Load project context
if [ -f ".claude/PROJECT_CONTEXT.md" ]; then
  echo "📋 Project context available"
fi

# Check git status
if git status --porcelain | grep -q .; then
  echo "⚠️  Uncommitted changes detected"
fi

# Load environment
if [ -f ".env" ]; then
  echo "🔐 Environment variables available"
fi

# Run pre-flight checks
if [ -f ".claude/hooks/pre-flight-check.sh" ]; then
  bash .claude/hooks/pre-flight-check.sh
fi

echo "✅ Session initialized"

Outputs:

Session initialization automation
Context loading
Environment validation

Validation:

[ ] Hook runs on session start
[ ] Context loaded correctly
[ ] Environment validated

Time Estimate: 15-20 minutes

Operation 7: Deploy and Manage Hooks

Purpose: Install, update, remove, and audit hooks

Process:

Deploy Hook (global or project):

# Deploy to global (~/.claude/hooks/)
deploy-hook --global formatting-hook.json

# Deploy to project (.claude/hooks/)
deploy-hook --project security-hook.json

List Active Hooks:

# List all hooks
ls -la ~/.claude/hooks/
ls -la .claude/hooks/

# Parse and display
for hook in .claude/hooks/*.json; do
  echo "Hook: $(basename $hook)"
  jq '.event, .description' $hook
done

Validate Hook:

# Test hook in safe environment
validate-hook formatting-hook.json

# Expected:
# ✅ JSON valid
# ✅ Handler command exists
# ✅ Event type valid
# ✅ Structured output correct

Remove Hook:

# Disable hook
rm .claude/hooks/formatting-hook.json

# Or rename to .disabled
mv .claude/hooks/security-hook.json .claude/hooks/security-hook.json.disabled

Outputs:

Hook deployment automation
Hook management interface
Validation before deployment

Validation:

[ ] Can deploy hooks globally and per-project
[ ] Can list active hooks
[ ] Can validate hooks safely
[ ] Can remove/disable hooks

Time Estimate: 30-45 minutes

Operation 8: Security Audit Hooks

Purpose: Review all active hooks for security issues

Process:

Audit All Hooks:

# Scan all hook files
for hook in ~/.claude/hooks/*.json .claude/hooks/*.json; do
  echo "Auditing: $hook"

  # Check for dangerous patterns
  if grep -q "rm -rf\|dd if\|curl.*sudo" $hook; then
    echo "⚠️  Dangerous command detected"
  fi

  # Check for credential leaks
  if grep -q "password\|secret\|token\|api_key" $hook; then
    echo "⚠️  Potential credential exposure"
  fi

  # Validate JSON structure
  jq empty $hook 2>/dev/null || echo "❌ Invalid JSON"
done

Generate Security Report:

# Hook Security Audit

## Hooks Scanned: 8

### HIGH RISK
None

### MEDIUM RISK
1. observability-hook.json
   - Issue: Sends data to external URL
   - Recommendation: Validate URL is trusted

### LOW RISK
2. formatting-hook.json
   - Info: Executes npx prettier (safe)

## Recommendations
- Review observability destination
- Consider encrypting telemetry data

Outputs:

Security audit report
Risk assessment
Recommendations

Validation:

[ ] All hooks scanned
[ ] Security issues identified
[ ] Recommendations provided

Time Estimate: 20-30 minutes

Hook Templates

Template 1: Auto-Format (PostToolUse)

{
  "event": "PostToolUse",
  "tools": ["Write", "Edit"],
  "description": "Auto-format code after Claude writes",
  "handler": {
    "command": "npx prettier --write \"$FILE\"",
    "timeout": 5000
  },
  "filters": {
    "filePatterns": ["**/*.{ts,tsx,js,jsx}"],
    "excludePatterns": ["node_modules/**", "dist/**", "build/**"]
  }
}

Impact: 92% reduction in style review time

Template 2: Security Gate (PreToolUse)

{
  "event": "PreToolUse",
  "tools": ["Write", "Edit", "Bash"],
  "description": "Block modifications to production files",
  "handler": {
    "command": ".claude/hooks/security-gate.sh \"$TOOL\" \"$FILE\" \"$COMMAND\""
  },
  "structuredOutput": true
}

Impact: Prevents accidental production damage

Template 3: Telemetry (Notification)

{
  "event": "Notification",
  "description": "Send telemetry on important events",
  "handler": {
    "command": ".claude/hooks/telemetry.sh \"$EVENT_TYPE\" \"$MESSAGE\""
  }
}

Impact: Full observability of AI agent behavior

Template 4: Validation (PreToolUse)

{
  "event": "PreToolUse",
  "tools": ["Write"],
  "description": "Validate JSON/YAML before writing",
  "handler": {
    "command": ".claude/hooks/validate-syntax.sh \"$FILE\" \"$CONTENT\""
  },
  "structuredOutput": true
}

Impact: Prevent invalid file writes

Template 5: Context Loading (SessionStart)

{
  "event": "SessionStart",
  "description": "Load project context on session start",
  "handler": {
    "command": ".claude/hooks/load-context.sh"
  }
}

Impact: Automatic context initialization

Template 6: Cleanup (SessionEnd)

{
  "event": "SessionEnd",
  "description": "Save state and cleanup on session end",
  "handler": {
    "command": ".claude/hooks/session-cleanup.sh"
  }
}

Impact: Automatic state preservation

Best Practices

1. Structured JSON Output (For Control)

Standard Exit Codes (Simple):

0: Continue
Non-zero: Block

Structured JSON (Advanced):

{
  "continue": false,
  "stopReason": "Custom blocking reason shown to user",
  "suppressOutput": true
}

When to Use:

Need custom error messages
Want to suppress default output
Complex control flow

2. MCP Tool Targeting

Patterns:

mcp__*: All MCP tools
mcp__server__*: All tools from specific server
mcp__server__tool: Specific tool only

Examples:

// Block all filesystem MCP
"tools": ["mcp__filesystem__*"]

// Block specific GitHub operation
"tools": ["mcp__github__delete_repository"]

// Allow specific, block others
"tools": ["mcp__github__*"],
"handler": "allow-list-check.sh"

3. File Pattern Filters

{
  "filePatterns": [
    "src/**/*.ts",           // Include source files
    "tests/**/*.test.ts"     // Include tests
  ],
  "excludePatterns": [
    "node_modules/**",       // Exclude dependencies
    "**/*.min.js",           // Exclude minified
    ".git/**"                // Exclude git internals
  ]
}

Tip: Start inclusive, add exclusions as needed

4. Performance Considerations

Hook Execution:

Hooks run synchronously (blocking)
Keep handlers fast (<5 seconds)
Use timeouts to prevent hangs
Async operations: spawn background process, return immediately

Example (Fast hook):

#!/bin/bash
# Quick validation
if [ ! -f "$FILE" ]; then
  echo '{"continue": false, "stopReason": "File does not exist"}'
  exit 1
fi
echo '{"continue": true}'
exit 0

Example (Slow operation - backgrounded):

#!/bin/bash
# Start slow operation in background
(sleep 10 && heavy-operation.sh "$FILE") &

# Return immediately
echo '{"continue": true}'
exit 0

5. Security Best Practices

Never in hooks:

Hardcode credentials
Execute untrusted input
Modify critical system files
Expose sensitive data in logs

Always in hooks:

Validate all inputs
Use allowlists (not denylists)
Log security events
Fail securely (deny by default)

Common Hook Patterns

Pattern 1: Code Quality Enforcement

PostToolUse Chain:

Write/Edit → Prettier (format) → ESLint (lint) → TypeScript (type check)

Implementation:

[
  {
    "event": "PostToolUse",
    "tools": ["Write", "Edit"],
    "handler": "npx prettier --write \"$FILE\""
  },
  {
    "event": "PostToolUse",
    "tools": ["Write", "Edit"],
    "handler": "npx eslint --fix \"$FILE\""
  }
]

Result: All AI code automatically meets quality standards

Pattern 2: Test-on-Save

PostToolUse Test Runner:

{
  "event": "PostToolUse",
  "tools": ["Write", "Edit"],
  "description": "Run tests after code changes",
  "handler": {
    "command": ".claude/hooks/run-tests.sh \"$FILE\""
  },
  "filters": {
    "filePatterns": ["src/**/*.ts"]
  }
}

run-tests.sh:

#!/bin/bash
FILE=$1

# Find corresponding test file
TEST_FILE="${FILE/.ts/.test.ts}"
TEST_FILE="${TEST_FILE/src\//tests\/}"

if [ -f "$TEST_FILE" ]; then
  npm test -- "$TEST_FILE" --silent
fi

Result: Immediate test feedback on every change

Pattern 3: Security Guardrails

Multi-Layer Security:

PreToolUse → Path traversal check → Permission check → Allowlist check → Allow/Block

Result: Comprehensive security enforcement

Pattern 4: Observability Pipeline

Multi-Hook Telemetry:

SessionStart → Log session init
PreToolUse → Log tool attempts
PostToolUse → Log tool results + timing
Notification → Log important events
SessionEnd → Log session summary + metrics

Result: Complete observability of AI behavior

Troubleshooting

Hook Not Firing

Checklist:

[ ] Hook file in correct location (~/.claude/hooks/ or .claude/hooks/)
[ ] Hook file is valid JSON (test with jq empty hook.json)
[ ] Event type correct (UserPromptSubmit, PreToolUse, etc.)
[ ] Tool name matches (case-sensitive)
[ ] Claude Code version supports hooks (June 2025+)

Debug:

# Test hook JSON
jq empty .claude/hooks/my-hook.json

# Check hook location
ls -la .claude/hooks/

# Test handler command manually
bash .claude/hooks/handler.sh "test args"

Hook Blocking Everything

Issue: PreToolUse hook with {"continue": false} blocks all operations

Fix:

Check handler script logic
Ensure conditions are correct
Add fallback: if unsure, allow (fail open vs. fail closed)
Test with specific files before deploying

Performance Impact

Issue: Hook adds 2-5 seconds to every operation

Solutions:

Optimize handler script (remove slow operations)
Use background processes for slow tasks
Add caching (don't re-validate unchanged files)
Set timeout limits
Consider removing hook if not valuable

Appendix A: Hook Event Reference

UserPromptSubmit

Trigger: Before Claude processes user prompt Use: Validate prompts, inject context, enhance prompts Variables: $PROMPT

PreToolUse

Trigger: Before tool execution Use: Security gates, validation, logging Variables: $TOOL, $FILE, $COMMAND, $CONTENT Control: Can block operation

PostToolUse

Trigger: After tool execution Use: Auto-format, linting, testing, cleanup Variables: $TOOL, $FILE, $RESULT

PermissionRequest

Trigger: When Claude requests permissions Use: Auto-approve safe operations, log requests Variables: $PERMISSION_TYPE

Notification

Trigger: Important events Use: Telemetry, alerting, logging Variables: $EVENT_TYPE, $MESSAGE

SessionStart

Trigger: Session initialization Use: Load context, validate environment Variables: None

SessionEnd

Trigger: Session termination Use: Save state, cleanup, metrics Variables: None

Stop

Trigger: Conversation stop Use: Final cleanup, state saving Variables: $REASON

Appendix B: Structured JSON Control

Basic Control (Exit Codes)

# Allow
exit 0

# Block
exit 1

Advanced Control (JSON)

{
  "continue": boolean,        // Allow operation?
  "stopReason": "string",     // Why blocked (shown to user)
  "suppressOutput": boolean   // Hide default blocking message?
}

When to Use JSON:

Custom error messages
Silent blocking
Complex control logic

Quick Reference

The 8 Hook Events

| Event | When | Use For | Can Block? | |-------|------|---------|------------| | UserPromptSubmit | Before prompt processed | Prompt validation/enhancement | Yes | | PreToolUse | Before tool runs | Security, validation | Yes | | PostToolUse | After tool runs | Format, lint, test | No | | PermissionRequest | Permissions requested | Auto-approve, logging | Yes | | Notification | Important events | Telemetry, alerts | No | | SessionStart | Session begins | Init, context load | No | | SessionEnd | Session ends | Cleanup, save state | No | | Stop | Conversation stops | Final cleanup | No |

Common Use Cases

| Use Case | Hook Event | Typical Impact | |----------|------------|----------------| | Auto-format code | PostToolUse | 92% style review reduction | | Security gates | PreToolUse | Prevent production damage | | Run tests on save | PostToolUse | Immediate feedback | | Observability | Notification | Full behavior tracking | | JSON validation | PreToolUse | Prevent invalid writes | | Context loading | SessionStart | Auto-initialization | | State saving | SessionEnd | Preserve progress | | MCP control | PreToolUse | Granular tool access |

hooks-manager enables transformative automation in Claude Code through event-driven hooks, reducing manual work by up to 92% while enforcing security, quality, and observability standards.

For templates, see examples/. For troubleshooting, see Troubleshooting section.

Agent Skills: Hooks Manager

Install this agent skill to your local

Skill Files

Hooks Manager

Overview

When to Use

Prerequisites

Required

Recommended

Hook Operations

Operation 1: Create Formatting Hook (PostToolUse)

Operation 2: Create Security Hook (PreToolUse)

Operation 3: Create Observability Hook (Notification)

Operation 4: Create Validation Hook (PreToolUse)

Operation 5: Create MCP Tool Hook (PreToolUse)

Operation 6: Create Comprehensive Hook (SessionStart)

Operation 7: Deploy and Manage Hooks

Operation 8: Security Audit Hooks

Hook Templates

Template 1: Auto-Format (PostToolUse)

Template 2: Security Gate (PreToolUse)

Template 3: Telemetry (Notification)

Template 4: Validation (PreToolUse)

Template 5: Context Loading (SessionStart)

Template 6: Cleanup (SessionEnd)

Best Practices

1. Structured JSON Output (For Control)

2. MCP Tool Targeting

3. File Pattern Filters

4. Performance Considerations

5. Security Best Practices

Common Hook Patterns

Pattern 1: Code Quality Enforcement

Pattern 2: Test-on-Save

Pattern 3: Security Guardrails

Pattern 4: Observability Pipeline

Troubleshooting

Hook Not Firing

Hook Blocking Everything

Performance Impact

Appendix A: Hook Event Reference

UserPromptSubmit

PreToolUse

PostToolUse

PermissionRequest

Notification

SessionStart

SessionEnd

Stop

Appendix B: Structured JSON Control

Basic Control (Exit Codes)

Advanced Control (JSON)

Quick Reference

The 8 Hook Events

Common Use Cases