Claude Code Hooks Configuration Skill

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:

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

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

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.

Agent Skills: Claude Code Hooks Configuration

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