hooks-configuration

Claude Code Hooks Configuration

Expert knowledge for configuring and developing Claude Code hooks to automate workflows and enforce best practices.

When to Use This Skill

Use this skill when...	Use something else when...
Configuring hook lifecycle events (PreToolUse, PostToolUse, etc.)	Writing general shell scripts unrelated to hooks
Blocking dangerous commands or enforcing patterns	Setting up CI/CD pipelines (use CI tooling)
Auto-formatting files after edits	Configuring Claude Code settings unrelated to hooks
Injecting context at session or subagent start	Writing standalone automation scripts
Setting up PermissionRequest auto-approve/deny	Managing project permissions via settings.json directly
Developing prompt or agent hooks for judgment-based decisions	Building MCP servers or custom tool integrations

Core Concepts

What Are Hooks? Hooks are user-defined shell commands that execute at specific points in Claude Code's lifecycle. Unlike relying on Claude to "decide" to run something, hooks provide deterministic, guaranteed execution.

Why Use Hooks?

• Enforce code formatting automatically
• Block dangerous commands before execution
• Inject context at session start
• Log commands for audit trails
• Send notifications when tasks complete

Hook Lifecycle Events

Event	When It Fires	Key Use Cases
SessionStart	Session begins/resumes	Environment setup, context loading
SessionEnd	Session terminates	Cleanup, state persistence
UserPromptSubmit	User submits prompt	Input validation, context injection
PreToolUse	Before tool execution	Permission control, blocking dangerous ops
PostToolUse	After tool completes	Auto-formatting, logging, validation
PostToolUseFailure	After tool execution fails	Retry decisions, error handling
PermissionRequest	Claude requests permission for a tool	Auto approve/deny without user prompt
Stop	Main agent finishes responding	Notifications, git reminders
SubagentStart	Subagent (Task tool) is about to start	Input modification, context injection
SubagentStop	Subagent finishes	Per-task completion evaluation
WorktreeCreate	New git worktree created via EnterWorktree	Worktree setup, dependency install
WorktreeRemove	Worktree removed after session exits	Cleanup, uncommitted changes alert
TeammateIdle	Teammate in agent team goes idle	Assign additional tasks to teammate
TaskCompleted	Task in shared task list marked complete	Validation gates before task acceptance
PreCompact	Before context compaction	Transcript backup
Notification	Claude sends notification	Custom alerts
ConfigChange	Claude Code settings change at runtime	Audit config changes, validation

Stop vs SubagentStop: Stop fires at the session level when the main agent finishes a response turn. SubagentStop fires when an individual subagent (spawned via the Task tool) completes. Use Stop for session-level notifications; use SubagentStop for per-task quality gates.

For full schemas, examples, and timeout recommendations for each event, see .claude/rules/hooks-reference.md.

Configuration

File Locations

Hooks are configured in settings files:

• ~/.claude/settings.json - User-level (applies everywhere)
• .claude/settings.json - Project-level (committed to repo)
• .claude/settings.local.json - Local project (not committed)

Claude Code merges all matching hooks from all files.

Frontmatter Hooks (Skills and Commands)

Hooks can also be defined directly in skill and command frontmatter using the hooks field:

---
name: my-skill
description: A skill with hooks
allowed-tools: Bash, Read
hooks:
  PreToolUse:
    - matcher: "Bash"
      hooks:
        - type: command
          command: "echo 'Pre-tool hook from skill'"
          timeout: 10
---

Basic Structure

{
  "hooks": {
    "EventName": [
      {
        "matcher": "ToolPattern",
        "hooks": [
          {
            "type": "command",
            "command": "your-command-here",
            "timeout": 30
          }
        ]
      }
    ]
  }
}

Matcher Patterns

• Exact match: "Bash" - matches exactly "Bash" tool
• Regex patterns: "Edit|Write" - matches either tool
• Wildcards: "Notebook.*" - matches tools starting with "Notebook"
• All tools: "*" - matches everything
• MCP tools: "mcp__server__tool" - targets MCP server tools

Input/Output Schema Summary

Hooks receive JSON via stdin with common fields (session_id, transcript_path, cwd, permission_mode, hook_event_name). Event-specific fields include tool_name and tool_input for PreToolUse, plus tool_response for PostToolUse, and subagent_type/subagent_prompt for SubagentStart.

Exit codes: 0 = allow, 2 = block (stderr shown to Claude), other = non-blocking error.

JSON responses vary by event: PreToolUse uses hookSpecificOutput with permissionDecision; Stop/SubagentStop use decision/reason; SubagentStart uses updatedPrompt; SessionStart uses hookSpecificOutput with additionalContext.

For detailed hook schemas and examples, see REFERENCE.md.

Common Hook Patterns

Block Dangerous Commands (PreToolUse)

#!/bin/bash
INPUT=$(cat)
COMMAND=$(echo "$INPUT" | jq -r '.tool_input.command // empty')

# Block rm -rf /
if echo "$COMMAND" | grep -Eq 'rm\s+(-rf|-fr)\s+/'; then
    echo "BLOCKED: Refusing to run destructive command on root" >&2
    exit 2
fi

exit 0

Auto-Format After Edits (PostToolUse)

#!/bin/bash
INPUT=$(cat)
FILE=$(echo "$INPUT" | jq -r '.tool_input.file_path // empty')

if [[ "$FILE" == *.py ]]; then
    ruff format "$FILE" 2>/dev/null
    ruff check --fix "$FILE" 2>/dev/null
elif [[ "$FILE" == *.ts ]] || [[ "$FILE" == *.tsx ]]; then
    prettier --write "$FILE" 2>/dev/null
fi

exit 0

Remind About Built-in Tools (PreToolUse)

#!/bin/bash
INPUT=$(cat)
COMMAND=$(echo "$INPUT" | jq -r '.tool_input.command // empty')

if echo "$COMMAND" | grep -Eq '^\s*cat\s+[^|><]'; then
    echo "REMINDER: Use the Read tool instead of 'cat'" >&2
    exit 2
fi

exit 0

Load Context at Session Start (SessionStart)

#!/bin/bash
GIT_STATUS=$(git status --short 2>/dev/null | head -5)
BRANCH=$(git branch --show-current 2>/dev/null)

CONTEXT="Current branch: $BRANCH\nPending changes:\n$GIT_STATUS"
jq -n --arg ctx "$CONTEXT" '{
  "hookSpecificOutput": {
    "hookEventName": "SessionStart",
    "additionalContext": $ctx
  }
}'

For additional patterns (subagent injection, desktop notifications, audit logging, auto-approve, worktree setup, task gating), see REFERENCE.md.

Prompt-Based and Agent-Based Hooks

Four hook types: command (shell script, exit code), http (HTTPS endpoint), prompt (single-turn LLM call), and agent (multi-turn with tool access). Use command for deterministic rules; prompt/agent for judgment-based decisions. Add async: true for fire-and-forget; once: true to run only once per session.

Prompt and agent hooks work on PreToolUse, PostToolUse, PostToolUseFailure, PermissionRequest, Stop, SubagentStop, TaskCompleted, UserPromptSubmit. All other events support command hooks only.

For hook type details, CLAUDE_ENV_FILE, and configuration examples, see REFERENCE.md and .claude/rules/prompt-agent-hooks.md.

Handling Blocked Commands

When a PreToolUse hook blocks a command:

Situation	Action
Hook suggests alternative	Use the suggested tool/approach
Alternative won't work	Ask user to run command manually
User says "proceed"	Still blocked - explain and provide command for manual execution

Critical: User permission does NOT bypass hooks. Retrying a blocked command will fail again.

When command is legitimately needed:

1. Explain why the command is required
2. Describe alternatives considered and why they won't work
3. Provide exact command for user to run manually
4. Let user decide

Timeout Guidelines

The default hook timeout is 600s (10 minutes) since Claude Code 2.1.50. Set explicit timeouts to document intent and prevent "Hook cancelled" errors:

Hook Type	Recommended Timeout	Use Case
SessionStart	120–300s	Tests, linters, dependency checks
SessionEnd	60–120s	Logging, cleanup, state saving
Stop / SubagentStop	30–60s	Git status checks, quick validations
PreToolUse	10–30s	Quick validations
PostToolUse	30–120s	Logging, notifications
PermissionRequest	5–15s	Keep fast for good UX

Background Subshell Pattern (Recommended for Slow Hooks)

When a hook needs to do slow work (logging, API calls) without blocking, run it in a background subshell:

#!/bin/bash
# Exits instantly; slow work continues in background
(
  echo "$(date): Session ended" >> ~/.claude/session.log
  # Any other slow work...
) &>/dev/null &
exit 0

Why this works: ( ) creates a subshell, & runs it in background, &>/dev/null prevents stdout/stderr from blocking, exit 0 returns success immediately.

Best Practices

Area	Key Points
Script	Read stdin with cat; parse with jq; quote all vars; exit 2 to block, 0 to allow; stderr for messages; keep < 5s
Config	$CLAUDE_PROJECT_DIR for portable paths; explicit timeouts; specific matchers over wildcards; test before enabling
Security	Validate all inputs; use absolute paths; avoid .env / .git/ directly; review before deploy

Debugging

Error	Cause	Fix
Hook cancelled	Timeout exceeded	Add "timeout" field or use background subshell pattern
Hook failed	Script error	Check exit code; add error handling
Command not found	Missing script	Verify script path and permissions
Permission denied	Script not executable	chmod +x ~/.claude/script.sh

Use /hooks to verify registration, claude --debug for verbose logging, and echo '{"tool_input":{"command":"..."}}' | bash your-hook.sh to test manually. Check $? for exit code. See hooks/README.md for plugin hook documentation.