Codeman/docs/claude-code-hooks-reference.md

Claude Code Hooks Reference

Official documentation for Claude Code hooks system, extracted from code.claude.com.

Last Updated: 2026-01-22 Source: Claude Code Hooks Documentation

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Overview

Hooks are automated scripts that execute at specific events during your Claude Code session. They allow you to:

• Validate, modify, or block tool usage
• Add context to prompts
• Implement custom workflows
• Control agent behavior

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Configuration

Hooks are configured in settings files:

File	Scope
~/.claude/settings.json	User (global)
.claude/settings.json	Project
.claude/settings.local.json	Local project (gitignored)
Plugin hook files	Plugin-specific

Basic Structure

{
  "hooks": {
    "EventName": [
      {
        "matcher": "ToolPattern",
        "hooks": [
          {
            "type": "command",
            "command": "your-command-here"
          }
        ]
      }
    ]
  }
}

Key Fields:

• matcher: Pattern to match tool names (case-sensitive, supports regex like Edit|Write or * for all)
• type: "command" for bash or "prompt" for LLM-based evaluation
• command: Bash command to execute
• prompt: LLM prompt for evaluation (prompt-based hooks only)
• timeout: Optional timeout in seconds (default: 60)

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Hook Events

PreToolUse

When: After Claude creates tool parameters, before processing the tool call.

Use Cases: Approval, denial, or modification of tool calls.

Common Matchers:

• Bash - Shell commands
• Write - File writing
• Edit - File editing
• Read - File reading
• Task - Subagent tasks
• WebFetch, WebSearch - Web operations
• mcp__<server>__<tool> - MCP tools

Output Control:

{
  "hookSpecificOutput": {
    "hookEventName": "PreToolUse",
    "permissionDecision": "allow|deny|ask",
    "permissionDecisionReason": "string",
    "updatedInput": {
      "field_to_modify": "new value"
    },
    "additionalContext": "Context for Claude"
  }
}

PermissionRequest

When: When the user is shown a permission dialog.

Use Cases: Auto-approve or deny permissions.

Output Control:

{
  "hookSpecificOutput": {
    "hookEventName": "PermissionRequest",
    "decision": {
      "behavior": "allow|deny",
      "updatedInput": { },
      "message": "deny reason",
      "interrupt": false
    }
  }
}

PostToolUse

When: Immediately after a tool completes successfully.

Use Cases: Provide feedback, run formatters/linters, log operations.

Output Control:

{
  "decision": "block",
  "reason": "Explanation",
  "hookSpecificOutput": {
    "hookEventName": "PostToolUse",
    "additionalContext": "Additional information"
  }
}

Notification

When: When Claude Code sends notifications.

Matchers:

• permission_prompt
• idle_prompt
• auth_success
• elicitation_dialog

UserPromptSubmit

When: When the user submits a prompt, before Claude processes it.

Use Cases: Add context, validate, or block prompts.

Output Control:

{
  "decision": "block",
  "reason": "Explanation",
  "hookSpecificOutput": {
    "hookEventName": "UserPromptSubmit",
    "additionalContext": "My additional context"
  }
}

Stop

When: When the main Claude Code agent finishes responding.

Important: Does NOT run on user interrupt.

Use Cases: Ralph Wiggum loops - block exit and refeed prompt.

Output Control:

{
  "decision": "block",
  "reason": "Must provide when blocking"
}

Or to allow exit:

{
  "continue": true,
  "stopReason": "optional message"
}

Note: For Stop events, "continue": false takes precedence over "decision": "block".

SubagentStop

When: When a subagent (Task tool call) finishes responding.

Use Cases: Control nested loops, verify subagent output.

PreCompact

When: Before a compact operation.

Matchers:

• manual - Invoked from /compact
• auto - Invoked from auto-compact

SessionStart

When: When Claude Code starts or resumes a session.

Matchers:

• startup - Fresh start
• resume - From --resume, --continue, or /resume
• clear - From /clear
• compact - From auto or manual compact

Use Cases: Load development context, set environment variables.

Persisting Environment Variables:

#!/bin/bash
if [ -n "$CLAUDE_ENV_FILE" ]; then
  echo 'export NODE_ENV=production' >> "$CLAUDE_ENV_FILE"
  echo 'export API_KEY=your-api-key' >> "$CLAUDE_ENV_FILE"
fi
exit 0

Output Control:

{
  "hookSpecificOutput": {
    "hookEventName": "SessionStart",
    "additionalContext": "Context to load"
  }
}

SessionEnd

When: When a session ends.

Reason Values:

• clear
• logout
• prompt_input_exit
• other

Use Cases: Cleanup tasks, logging.

---

Hook Input

Hooks receive JSON via stdin with common fields:

{
  "session_id": "abc123",
  "transcript_path": "/path/to/transcript.jsonl",
  "cwd": "/current/directory",
  "permission_mode": "default",
  "hook_event_name": "PreToolUse",
  "tool_name": "Bash",
  "tool_input": { },
  "tool_use_id": "toolu_01ABC123..."
}

Tool-Specific Input

Bash:

{
  "tool_name": "Bash",
  "tool_input": {
    "command": "psql -c 'SELECT * FROM users'",
    "description": "Query the users table",
    "timeout": 120000
  }
}

Write:

{
  "tool_name": "Write",
  "tool_input": {
    "file_path": "/path/to/file.txt",
    "content": "file content"
  }
}

Edit:

{
  "tool_name": "Edit",
  "tool_input": {
    "file_path": "/path/to/file.txt",
    "old_string": "original text",
    "new_string": "replacement text"
  }
}

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Hook Output

Exit Codes

Code	Behavior
0	Success. stdout processed (shown in verbose or added as context)
2	Blocking error. Only stderr used. Blocks tool/prompt based on event
Other	Non-blocking error. stderr shown in verbose, execution continues

JSON Output (Exit Code 0)

{
  "continue": true,
  "stopReason": "optional message",
  "suppressOutput": true,
  "systemMessage": "optional warning"
}

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Prompt-Based Hooks

For Stop and SubagentStop events, you can use LLM-based evaluation:

{
  "hooks": {
    "Stop": [
      {
        "hooks": [
          {
            "type": "prompt",
            "prompt": "Should Claude stop? Context: $ARGUMENTS\n\nCheck if all tasks are complete.",
            "timeout": 30
          }
        ]
      }
    ]
  }
}

LLM Response Format:

{
  "ok": true,
  "reason": "Explanation when ok is false"
}

---

Component-Scoped Hooks

Hooks can be defined in Skills, Agents, and Slash Commands using frontmatter:

---
name: secure-operations
hooks:
  PreToolUse:
    - matcher: "Bash"
      hooks:
        - type: command
          command: "./scripts/security-check.sh"
---

These hooks:

• Are scoped to the component's lifecycle
• Only run when that component is active
• Support: PreToolUse, PostToolUse, Stop

---

MCP Tools

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

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

---

Examples

Bash Command Validation

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

VALIDATION_RULES = [
    (r"\bgrep\b(?!.*\|)", "Use 'rg' instead of 'grep'"),
    (r"\bfind\s+\S+\s+-name\b", "Use 'rg --files' instead of 'find -name'"),
]

try:
    input_data = json.load(sys.stdin)
except json.JSONDecodeError as e:
    print(f"Error: {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)

issues = []
for pattern, message in VALIDATION_RULES:
    if re.search(pattern, command):
        issues.append(message)

if issues:
    for message in issues:
        print(f"- {message}", file=sys.stderr)
    sys.exit(2)

Auto-Approve Documentation Reads

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

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

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

if tool_name == "Read":
    file_path = tool_input.get("file_path", "")
    if file_path.endswith((".md", ".mdx", ".txt", ".json")):
        output = {
            "hookSpecificOutput": {
                "hookEventName": "PreToolUse",
                "permissionDecision": "allow",
                "permissionDecisionReason": "Documentation file auto-approved"
            },
            "suppressOutput": True
        }
        print(json.dumps(output))
        sys.exit(0)

sys.exit(0)

Post-Write Formatter

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          {
            "type": "command",
            "command": "npx prettier --write \"$TOOL_INPUT_FILE_PATH\" 2>/dev/null || true"
          }
        ]
      }
    ]
  }
}

Ralph Wiggum Stop Hook

#!/bin/bash
# ralph-stop-hook.sh

STATE_FILE=".claude/ralph-loop.local.md"

# Check if state file exists
if [ ! -f "$STATE_FILE" ]; then
    exit 0  # No active loop, allow exit
fi

# Read state from YAML frontmatter
ENABLED=$(grep -m1 "^enabled:" "$STATE_FILE" | cut -d' ' -f2)
ITERATION=$(grep -m1 "^iteration:" "$STATE_FILE" | cut -d' ' -f2)
MAX_ITER=$(grep -m1 "^max-iterations:" "$STATE_FILE" | cut -d' ' -f2)
PROMISE=$(grep -m1 "^completion-promise:" "$STATE_FILE" | cut -d' ' -f2-)

# Check if disabled
if [ "$ENABLED" = "false" ]; then
    exit 0
fi

# Check max iterations
if [ -n "$MAX_ITER" ] && [ "$ITERATION" -ge "$MAX_ITER" ]; then
    exit 0
fi

# Check for completion promise in output
if [ -n "$PROMISE" ]; then
    if echo "$CLAUDE_OUTPUT" | grep -q "<promise>$PROMISE</promise>"; then
        exit 0
    fi
fi

# Block exit, increment iteration
NEW_ITER=$((ITERATION + 1))
sed -i "s/^iteration:.*/iteration: $NEW_ITER/" "$STATE_FILE"

# Output block decision
echo '{"decision": "block", "reason": "Completion promise not found. Iteration '"$NEW_ITER"'."}'
exit 0

---

Environment Variables

Variable	Description
CLAUDE_PROJECT_DIR	Project root directory
CLAUDE_CODE_REMOTE	"true" for web, empty for CLI
CLAUDE_ENV_FILE	Path to write persistent env vars (SessionStart)

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Debugging

Use claude --debug to see detailed hook execution:

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

Use /hooks command to view registered hooks and make changes.

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Execution Details

• Timeout: 60-second default per hook, configurable
• Parallelization: All matching hooks run in parallel
• Deduplication: Identical commands deduplicated automatically
• Matchers: Only apply to tool-based hooks (PreToolUse, PostToolUse, PostToolUseFailure, PermissionRequest)

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Security Best Practices

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)
5. Skip sensitive files - Avoid .env, .git/, keys, etc.

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Source: Claude Code Hooks Documentation