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Hooks reference

This page provides reference documentation for implementing hooks in Claude Code.

For a quickstart guide with examples, see Get started with Claude Code hooks.

Configuration

Claude Code hooks are configured in your settings files:

  • ~/.claude/settings.json - User settings
  • .claude/settings.json - Project settings
  • .claude/settings.local.json - Local project settings (not committed)
  • Enterprise managed policy settings

Structure

Hooks are organized by matchers, where each matcher can have multiple hooks:

{
  "hooks": {
    "EventName": [
      {
        "matcher": "ToolPattern",
        "hooks": [
          {
            "type": "command",
            "command": "your-command-here"
          }
        ]
      }
    ]
  }
}
  • matcher: Pattern to match tool names, case-sensitive (only applicable for PreToolUse and PostToolUse)
  • Simple strings match exactly: Write matches only the Write tool
  • Supports regex: Edit|Write or Notebook.*
  • Use * to match all tools. You can also use empty string ("") or leave matcher blank.
  • hooks: Array of commands to execute when the pattern matches
  • type: Currently only "command" is supported
  • command: The bash command to execute (can use $CLAUDE_PROJECT_DIR environment variable)
  • timeout: (Optional) How long a command should run, in seconds, before canceling that specific command.

For events like UserPromptSubmit, Notification, Stop, and SubagentStop that don't use matchers, you can omit the matcher field:

{
  "hooks": {
    "UserPromptSubmit": [
      {
        "hooks": [
          {
            "type": "command",
            "command": "/path/to/prompt-validator.py"
          }
        ]
      }
    ]
  }
}

Project-Specific Hook Scripts

You can use the environment variable CLAUDE_PROJECT_DIR (only available when Claude Code spawns the hook command) to reference scripts stored in your project, ensuring they work regardless of Claude's current directory:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Write|Edit",
        "hooks": [
          {
            "type": "command",
            "command": "$CLAUDE_PROJECT_DIR/.claude/hooks/check-style.sh"
          }
        ]
      }
    ]
  }
}

Hook Events

PreToolUse

Runs after Claude creates tool parameters and before processing the tool call.

Common matchers:

  • Task - Subagent tasks (see subagents documentation)
  • Bash - Shell commands
  • Glob - File pattern matching
  • Grep - Content search
  • Read - File reading
  • Edit, MultiEdit - File editing
  • Write - File writing
  • WebFetch, WebSearch - Web operations

PostToolUse

Runs immediately after a tool completes successfully.

Recognizes the same matcher values as PreToolUse.

Notification

Runs when Claude Code sends notifications. Notifications are sent when:

  1. Claude needs your permission to use a tool. Example: "Claude needs your permission to use Bash"
  2. The prompt input has been idle for at least 60 seconds. "Claude is waiting for your input"

UserPromptSubmit

Runs when the user submits a prompt, before Claude processes it. This allows you to add additional context based on the prompt/conversation, validate prompts, or block certain types of prompts.

Stop

Runs when the main Claude Code agent has finished responding. Does not run if the stoppage occurred due to a user interrupt.

SubagentStop

Runs when a Claude Code subagent (Task tool call) has finished responding.

PreCompact

Runs before Claude Code is about to run a compact operation.

Matchers:

  • manual - Invoked from /compact
  • auto - Invoked from auto-compact (due to full context window)

SessionStart

Runs when Claude Code starts a new session or resumes an existing session (which currently does start a new session under the hood). Useful for loading in development context like existing issues or recent changes to your codebase.

Matchers:

  • startup - Invoked from startup
  • resume - Invoked from --resume, --continue, or /resume
  • clear - Invoked from /clear
  • compact - Invoked from auto or manual compact.

SessionEnd

Runs when a Claude Code session ends. Useful for cleanup tasks, logging session statistics, or saving session state.

The reason field in the hook input will be one of:

  • clear - Session cleared with /clear command
  • logout - User logged out
  • prompt_input_exit - User exited while prompt input was visible
  • other - Other exit reasons

Hook Input

Hooks receive JSON data via stdin containing session information and event-specific data:

{
  // Common fields
  session_id: string
  transcript_path: string  // Path to conversation JSON
  cwd: string              // The current working directory when the hook is invoked

  // Event-specific fields
  hook_event_name: string
  ...
}

PreToolUse Input

The exact schema for tool_input depends on the tool.

{
  "session_id": "abc123",
  "transcript_path": "/Users/.../.claude/projects/.../00893aaf-19fa-41d2-8238-13269b9b3ca0.jsonl",
  "cwd": "/Users/...",
  "hook_event_name": "PreToolUse",
  "tool_name": "Write",
  "tool_input": {
    "file_path": "/path/to/file.txt",
    "content": "file content"
  }
}

PostToolUse Input

The exact schema for tool_input and tool_response depends on the tool.

{
  "session_id": "abc123",
  "transcript_path": "/Users/.../.claude/projects/.../00893aaf-19fa-41d2-8238-13269b9b3ca0.jsonl",
  "cwd": "/Users/...",
  "hook_event_name": "PostToolUse",
  "tool_name": "Write",
  "tool_input": {
    "file_path": "/path/to/file.txt",
    "content": "file content"
  },
  "tool_response": {
    "filePath": "/path/to/file.txt",
    "success": true
  }
}

Notification Input

{
  "session_id": "abc123",
  "transcript_path": "/Users/.../.claude/projects/.../00893aaf-19fa-41d2-8238-13269b9b3ca0.jsonl",
  "cwd": "/Users/...",
  "hook_event_name": "Notification",
  "message": "Task completed successfully"
}

UserPromptSubmit Input

{
  "session_id": "abc123",
  "transcript_path": "/Users/.../.claude/projects/.../00893aaf-19fa-41d2-8238-13269b9b3ca0.jsonl",
  "cwd": "/Users/...",
  "hook_event_name": "UserPromptSubmit",
  "prompt": "Write a function to calculate the factorial of a number"
}

Stop and SubagentStop Input

stop_hook_active is true when Claude Code is already continuing as a result of a stop hook. Check this value or process the transcript to prevent Claude Code from running indefinitely.

{
  "session_id": "abc123",
  "transcript_path": "~/.claude/projects/.../00893aaf-19fa-41d2-8238-13269b9b3ca0.jsonl",
  "hook_event_name": "Stop",
  "stop_hook_active": true
}

PreCompact Input

For manual, custom_instructions comes from what the user passes into /compact. For auto, custom_instructions is empty.

{
  "session_id": "abc123",
  "transcript_path": "~/.claude/projects/.../00893aaf-19fa-41d2-8238-13269b9b3ca0.jsonl",
  "hook_event_name": "PreCompact",
  "trigger": "manual",
  "custom_instructions": ""
}

SessionStart Input

{
  "session_id": "abc123",
  "transcript_path": "~/.claude/projects/.../00893aaf-19fa-41d2-8238-13269b9b3ca0.jsonl",
  "hook_event_name": "SessionStart",
  "source": "startup"
}

SessionEnd Input

{
  "session_id": "abc123",
  "transcript_path": "~/.claude/projects/.../00893aaf-19fa-41d2-8238-13269b9b3ca0.jsonl",
  "cwd": "/Users/...",
  "hook_event_name": "SessionEnd",
  "reason": "exit"
}

Hook Output

There are two ways for hooks to return output back to Claude Code. The output communicates whether to block and any feedback that should be shown to Claude and the user.

Simple: Exit Code

Hooks communicate status through exit codes, stdout, and stderr:

  • Exit code 0: Success. stdout is shown to the user in transcript mode (CTRL-R), except for UserPromptSubmit and SessionStart, where stdout is added to the context.
  • Exit code 2: Blocking error. stderr is fed back to Claude to process automatically. See per-hook-event behavior below.
  • Other exit codes: Non-blocking error. stderr is shown to the user and execution continues.

Reminder: Claude Code does not see stdout if the exit code is 0, except for the UserPromptSubmit hook where stdout is injected as context.

Exit Code 2 Behavior

Hook Event Behavior
PreToolUse Blocks the tool call, shows stderr to Claude
PostToolUse Shows stderr to Claude (tool already ran)
Notification N/A, shows stderr to user only
UserPromptSubmit Blocks prompt processing, erases prompt, shows stderr to user only
Stop Blocks stoppage, shows stderr to Claude
SubagentStop Blocks stoppage, shows stderr to Claude subagent
PreCompact N/A, shows stderr to user only
SessionStart N/A, shows stderr to user only
SessionEnd N/A, shows stderr to user only

Advanced: JSON Output

Hooks can return structured JSON in stdout for more sophisticated control:

Common JSON Fields

All hook types can include these optional fields:

{
  "continue": true, // Whether Claude should continue after hook execution (default: true)
  "stopReason": "string", // Message shown when continue is false

  "suppressOutput": true, // Hide stdout from transcript mode (default: false)
  "systemMessage": "string" // Optional warning message shown to the user
}

If continue is false, Claude stops processing after the hooks run.

  • For PreToolUse, this is different from "permissionDecision": "deny", which only blocks a specific tool call and provides automatic feedback to Claude.
  • For PostToolUse, this is different from "decision": "block", which provides automated feedback to Claude.
  • For UserPromptSubmit, this prevents the prompt from being processed.
  • For Stop and SubagentStop, this takes precedence over any "decision": "block" output.
  • In all cases, "continue" = false takes precedence over any "decision": "block" output.

stopReason accompanies continue with a reason shown to the user, not shown to Claude.

PreToolUse Decision Control

PreToolUse hooks can control whether a tool call proceeds.

  • "allow" bypasses the permission system. permissionDecisionReason is shown to the user but not to Claude.
  • "deny" prevents the tool call from executing. permissionDecisionReason is shown to Claude.
  • "ask" asks the user to confirm the tool call in the UI. permissionDecisionReason is shown to the user but not to Claude.
{
  "hookSpecificOutput": {
    "hookEventName": "PreToolUse",
    "permissionDecision": "allow" | "deny" | "ask",
    "permissionDecisionReason": "My reason here"
  }
}

The decision and reason fields are deprecated for PreToolUse hooks. Use hookSpecificOutput.permissionDecision and hookSpecificOutput.permissionDecisionReason instead. The deprecated fields "approve" and "block" map to "allow" and "deny" respectively.

PostToolUse Decision Control

PostToolUse hooks can provide feedback to Claude after tool execution.

  • "block" automatically prompts Claude with reason.
  • undefined does nothing. reason is ignored.
  • "hookSpecificOutput.additionalContext" adds context for Claude to consider.
{
  "decision": "block" | undefined,
  "reason": "Explanation for decision",
  "hookSpecificOutput": {
    "hookEventName": "PostToolUse",
    "additionalContext": "Additional information for Claude"
  }
}

UserPromptSubmit Decision Control

UserPromptSubmit hooks can control whether a user prompt is processed.

  • "block" prevents the prompt from being processed. The submitted prompt is erased from context. "reason" is shown to the user but not added to context.
  • undefined allows the prompt to proceed normally. "reason" is ignored.
  • "hookSpecificOutput.additionalContext" adds the string to the context if not blocked.
{
  "decision": "block" | undefined,
  "reason": "Explanation for decision",
  "hookSpecificOutput": {
    "hookEventName": "UserPromptSubmit",
    "additionalContext": "My additional context here"
  }
}

Stop/SubagentStop Decision Control

Stop and SubagentStop hooks can control whether Claude must continue.

  • "block" prevents Claude from stopping. You must populate reason for Claude to know how to proceed.
  • undefined allows Claude to stop. reason is ignored.
{
  "decision": "block" | undefined,
  "reason": "Must be provided when Claude is blocked from stopping"
}

SessionStart Decision Control

SessionStart hooks allow you to load in context at the start of a session.

  • "hookSpecificOutput.additionalContext" adds the string to the context.
  • Multiple hooks' additionalContext values are concatenated.
{
  "hookSpecificOutput": {
    "hookEventName": "SessionStart",
    "additionalContext": "My additional context here"
  }
}

SessionEnd Decision Control

SessionEnd hooks run when a session ends. They cannot block session termination but can perform cleanup tasks.

Exit Code Example: Bash Command Validation

#!/usr/bin/env python3
import json
import re
import sys

# Define validation rules as a list of (regex pattern, message) tuples
VALIDATION_RULES = [
    (
        r"\bgrep\b(?!.*\|)",
        "Use 'rg' (ripgrep) instead of 'grep' for better performance and features",
    ),
    (
        r"\bfind\s+\S+\s+-name\b",
        "Use 'rg --files | rg pattern' or 'rg --files -g pattern' instead of 'find -name' for better performance",
    ),
]


def validate_command(command: str) -> list[str]:
    issues = []
    for pattern, message in VALIDATION_RULES:
        if re.search(pattern, command):
            issues.append(message)
    return issues


try:
    input_data = json.load(sys.stdin)
except json.JSONDecodeError as e:
    print(f"Error: Invalid JSON input: {e}", file=sys.stderr)
    sys.exit(1)

tool_name = input_data.get("tool_name", "")
tool_input = input_data.get("tool_input", {})
command = tool_input.get("command", "")

if tool_name != "Bash" or not command:
    sys.exit(1)

# Validate the command
issues = validate_command(command)

if issues:
    for message in issues:
        print(f"• {message}", file=sys.stderr)
    # Exit code 2 blocks tool call and shows stderr to Claude
    sys.exit(2)

JSON Output Example: UserPromptSubmit to Add Context and Validation

For UserPromptSubmit hooks, you can inject context using either method:

  • Exit code 0 with stdout: Claude sees the context (special case for UserPromptSubmit)
  • JSON output: Provides more control over the behavior 
#!/usr/bin/env python3
import json
import sys
import re
import datetime

# Load input from stdin
try:
    input_data = json.load(sys.stdin)
except json.JSONDecodeError as e:
    print(f"Error: Invalid JSON input: {e}", file=sys.stderr)
    sys.exit(1)

prompt = input_data.get("prompt", "")

# Check for sensitive patterns
sensitive_patterns = [
    (r"(?i)\b(password|secret|key|token)\s*[:=]", "Prompt contains potential secrets"),
]

for pattern, message in sensitive_patterns:
    if re.search(pattern, prompt):
        # Use JSON output to block with a specific reason
        output = {
            "decision": "block",
            "reason": f"Security policy violation: {message}. Please rephrase your request without sensitive information."
        }
        print(json.dumps(output))
        sys.exit(0)

# Add current time to context
context = f"Current time: {datetime.datetime.now()}"
print(context)

"""
The following is also equivalent:
print(json.dumps({
  "hookSpecificOutput": {
    "hookEventName": "UserPromptSubmit",
    "additionalContext": context,
  },
}))
"""

# Allow the prompt to proceed with the additional context
sys.exit(0)

JSON Output Example: PreToolUse with Approval

#!/usr/bin/env python3
import json
import sys

# Load input from stdin
try:
    input_data = json.load(sys.stdin)
except json.JSONDecodeError as e:
    print(f"Error: Invalid JSON input: {e}", file=sys.stderr)
    sys.exit(1)

tool_name = input_data.get("tool_name", "")
tool_input = input_data.get("tool_input", {})

# Example: Auto-approve file reads for documentation files
if tool_name == "Read":
    file_path = tool_input.get("file_path", "")
    if file_path.endswith((".md", ".mdx", ".txt", ".json")):
        # Use JSON output to auto-approve the tool call
        output = {
            "decision": "approve",
            "reason": "Documentation file auto-approved",
            "suppressOutput": True  # Don't show in transcript mode
        }
        print(json.dumps(output))
        sys.exit(0)

# For other cases, let the normal permission flow proceed
sys.exit(0)

Working with MCP Tools

Claude Code hooks work seamlessly with Model Context Protocol (MCP) tools. When MCP servers provide tools, they appear with a special naming pattern that you can match in your hooks.

MCP Tool Naming

MCP tools follow the pattern mcp__<server>__<tool>, for example:

  • mcp__memory__create_entities - Memory server's create entities tool
  • mcp__filesystem__read_file - Filesystem server's read file tool
  • mcp__github__search_repositories - GitHub server's search tool

Configuring Hooks for MCP Tools

You can target specific MCP tools or entire MCP servers:

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "mcp__memory__.*",
        "hooks": [
          {
            "type": "command",
            "command": "echo 'Memory operation initiated' >> ~/mcp-operations.log"
          }
        ]
      },
      {
        "matcher": "mcp__.*__write.*",
        "hooks": [
          {
            "type": "command",
            "command": "/home/user/scripts/validate-mcp-write.py"
          }
        ]
      }
    ]
  }
}

Examples

For practical examples including code formatting, notifications, and file protection, see More Examples in the get started guide.

Security Considerations

Disclaimer

USE AT YOUR OWN RISK: Claude Code hooks execute arbitrary shell commands on your system automatically. By using hooks, you acknowledge that:

  • You are solely responsible for the commands you configure
  • Hooks can modify, delete, or access any files your user account can access
  • Malicious or poorly written hooks can cause data loss or system damage
  • Anthropic provides no warranty and assumes no liability for any damages resulting from hook usage
  • You should thoroughly test hooks in a safe environment before production use

Always review and understand any hook commands before adding them to your configuration.

Security Best Practices

Here are some key practices for writing more secure hooks:

  1. Validate and sanitize inputs - Never trust input data blindly
  2. Always quote shell variables - Use "$VAR" not $VAR
  3. Block path traversal - Check for .. in file paths
  4. Use absolute paths - Specify full paths for scripts (use $CLAUDE_PROJECT_DIR for the project path)
  5. Skip sensitive files - Avoid .env, .git/, keys, etc.

Configuration Safety

Direct edits to hooks in settings files don't take effect immediately. Claude Code:

  1. Captures a snapshot of hooks at startup
  2. Uses this snapshot throughout the session
  3. Warns if hooks are modified externally
  4. Requires review in /hooks menu for changes to apply

This prevents malicious hook modifications from affecting your current session.

Hook Execution Details

  • Timeout: 60-second execution limit by default, configurable per command.
  • A timeout for an individual command does not affect the other commands.
  • Parallelization: All matching hooks run in parallel
  • Deduplication: Multiple identical hook commands are deduplicated automatically
  • Environment: Runs in current directory with Claude Code's environment
  • The CLAUDE_PROJECT_DIR environment variable is available and contains the absolute path to the project root directory (where Claude Code was started)
  • Input: JSON via stdin
  • Output:
  • PreToolUse/PostToolUse/Stop/SubagentStop: Progress shown in transcript (Ctrl-R)
  • Notification/SessionEnd: Logged to debug only (--debug)
  • UserPromptSubmit/SessionStart: stdout added as context for Claude

Debugging

Basic Troubleshooting

If your hooks aren't working:

  1. Check configuration - Run /hooks to see if your hook is registered
  2. Verify syntax - Ensure your JSON settings are valid
  3. Test commands - Run hook commands manually first
  4. Check permissions - Make sure scripts are executable
  5. Review logs - Use claude --debug to see hook execution details

Common issues:

  • Quotes not escaped - Use \" inside JSON strings
  • Wrong matcher - Check tool names match exactly (case-sensitive)
  • Command not found - Use full paths for scripts

Advanced Debugging

For complex hook issues:

  1. Inspect hook execution - Use claude --debug to see detailed hook execution
  2. Validate JSON schemas - Test hook input/output with external tools
  3. Check environment variables - Verify Claude Code's environment is correct
  4. Test edge cases - Try hooks with unusual file paths or inputs
  5. Monitor system resources - Check for resource exhaustion during hook execution
  6. Use structured logging - Implement logging in your hook scripts

Debug Output Example

Use claude --debug to see hook execution details:

[DEBUG] Executing hooks for PostToolUse:Write
[DEBUG] Getting matching hook commands for PostToolUse with query: Write
[DEBUG] Found 1 hook matchers in settings
[DEBUG] Matched 1 hooks for query "Write"
[DEBUG] Found 1 hook commands to execute
[DEBUG] Executing hook command: <Your command> with timeout 60000ms
[DEBUG] Hook command completed with status 0: <Your stdout>

Progress messages appear in transcript mode (Ctrl-R) showing:

  • Which hook is running
  • Command being executed
  • Success/failure status
  • Output or error messages