jamie-bitflight/hooks-core-reference

Claude Code Hooks — Core Reference (January 2026)

Hooks execute custom commands or prompts in response to Claude Code events. Use for automation, validation, formatting, and security.

For JSON input/output schemas, activate Skill(skill: "plugin-creator:hooks-io-api"). For working examples and patterns, activate Skill(skill: "plugin-creator:hooks-patterns").

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All Hook Events

| Event | When Fired | Matcher Applies | Common Uses | | -------------------- | ------------------------------------------------------------ | -------------------------------------- | ----------------------- | | PreToolUse | Before tool execution | Yes — tool name | Validation, blocking | | PermissionRequest | When user shown permission dialog | Yes — tool name | Auto-approval policies | | PostToolUse | After successful tool execution | Yes — tool name | Formatting, linting | | PostToolUseFailure | After tool fails | Yes — tool name | Error handling | | Notification | When Claude wants attention | Yes — notification type | Custom notifications | | UserPromptSubmit | User submits prompt | No | Input validation | | UserPromptExpansion| Slash command expands into a full prompt | Yes — command name | Block expansions, inject context | | Stop | Claude finishes response | No | Cleanup, final checks | | SubagentStart | When spawning a subagent | Yes — agent type name | Subagent initialization | | SubagentStop | Subagent (Agent tool) completes | Yes — agent type name | Result validation | | TeammateIdle | Agent team teammate about to go idle | No | Quality gates | | TaskCompleted | Task being marked as completed | No | Completion enforcement | | InstructionsLoaded | CLAUDE.md or rules file loaded into context | No | Observability | | ConfigChange | Configuration file changes during session | Yes — config source | Settings auditing | | WorktreeCreate | Worktree being created (--worktree or isolation: worktree) | No | Custom VCS integration | | WorktreeRemove | Worktree being removed at session exit or subagent finish | No | Custom VCS cleanup | | PreCompact | Before context compaction | Yes — manual or auto | State backup | | PostCompact | After context compaction completes | Yes — manual or auto | React to new state | | Elicitation | MCP server requests user input mid-task | Yes — MCP server name | Programmatic responses | | ElicitationResult | User responds to MCP elicitation | Yes — MCP server name | Observe/modify response | | Setup | Repository setup/maintenance | Yes — init or maintenance | One-time operations | | CwdChanged | Working directory changes during session | No | Reload env, activate toolchains | | FileChanged | Watched file changes on disk | Yes — literal filename pattern | Monitor .env, direnv integration | | PermissionDenied | Auto mode classifier denies a tool call | Yes — tool name | Log denials, allow retry | | SessionStart | Session begins or resumes | Yes — startup, resume, etc. | Environment setup | | SessionEnd | Session ends | Yes — exit reason | Cleanup, persistence |

Note: The Agent tool was renamed from Task in Claude Code v2.1.63. Use Agent as the matcher name for tool-based hooks targeting subagent operations.

For a visual overview of the full event sequence, see the ../hooks-guide/references/hooks-lifecycle.png.

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Configuration

Configuration Locations (Precedence highest to lowest)

1. Managed - managed-settings.json (enterprise)
2. Local - .claude/settings.local.json (gitignored)
3. Project - .claude/settings.json (shared via git)
4. User - ~/.claude/settings.json (personal)
5. Plugin - hooks/hooks.json or frontmatter
6. Capability - Skill/Command/Agent frontmatter

Note: Enterprise administrators can use allowManagedHooksOnly to block user, project, and plugin hooks.

Structure

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

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

Fields:

• matcher: Pattern to match tool names, case-sensitive (for PreToolUse, PermissionRequest, PostToolUse); matches agent type name for SubagentStart/SubagentStop; matches exit reason for SessionEnd; matches config source for ConfigChange; matches MCP server name for Elicitation/ElicitationResult
  • Simple strings match exactly: Write matches only the Write tool
  • Supports regex: Edit|Write or Notebook.*
  • Use * to match all tools. Also accepts empty string ("") or omit matcher
• hooks: Array of hooks to execute when pattern matches
  • type: "command" for bash commands, "prompt" for LLM evaluation, "http" for HTTP POST requests, or "agent" for agentic verifiers with tool access
  • command: (For type: "command") The bash command to execute
  • url: (For type: "http") The URL to POST the hook input to
  • prompt: (For type: "prompt" or type: "agent") The prompt to send to the model
  • timeout: (Optional) Seconds before canceling (default: 600 for commands, 30 for prompts, 60 for agent hooks)
  • async: (For type: "command") If true, runs in background without blocking Claude
  • asyncRewake: (For type: "command") If true, runs in background and wakes Claude when process exits with code 2 — stderr/stdout delivered as a system reminder

Project-Specific Hook Scripts

Use $CLAUDE_PROJECT_DIR to reference scripts in your project:

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

Events Without Matchers

For UserPromptSubmit and Stop, omit the matcher. SubagentStart and SubagentStop support matchers filtered by agent type name. SessionEnd supports matchers filtered by exit reason. Example for events that don't use matchers:

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

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Event-Specific Matchers

PreToolUse / PermissionRequest / PostToolUse Common Matchers

| Matcher | Description | | ------------------- | ------------------------------ | | Agent | Subagent operations | | Bash | Shell commands | | Glob | File pattern matching | | Grep | Content search | | Read | File reading | | Edit | File editing | | Write | File writing | | WebFetch | Web fetching | | WebSearch | Web search | | Notebook.* | NotebookEdit, NotebookRead | | mcp__<server>__.* | All tools from MCP server | | mcp__.*__write.* | MCP write tools across servers |

SessionStart Matchers

| Matcher | Trigger | | --------- | -------------------------------------- | | startup | New session started | | resume | --resume, --continue, or /resume | | clear | /clear command | | compact | Auto or manual compact |

PreCompact Matchers

| Matcher | Trigger | | -------- | --------------------------- | | manual | /compact command | | auto | Auto-compact (full context) |

Setup Matchers

| Matcher | Trigger | | ------------- | ------------------------------- | | init | --init or --init-only flags | | maintenance | --maintenance flag |

SubagentStart / SubagentStop Matchers

Matched against the agent type name. Values include built-in agents (Bash, Explore, Plan) and custom agent names from .claude/agents/.

Note: The Agent tool was renamed from Task in Claude Code v2.1.63. Use Agent as the matcher name for PreToolUse/PostToolUse hooks targeting the subagent-spawning tool call.

SessionEnd Matchers

| Matcher | Trigger | | ------------------------------ | ---------------------------------------------- | | clear | Session cleared with /clear command | | logout | User logged out | | prompt_input_exit | User exited while prompt input was visible | | bypass_permissions_disabled | Bypass permissions mode was disabled | | other | Other exit reasons |

ConfigChange Matchers

| Matcher | When it fires | | ------------------- | ----------------------------------------- | | user_settings | ~/.claude/settings.json changes | | project_settings | .claude/settings.json changes | | local_settings | .claude/settings.local.json changes | | policy_settings | Managed policy settings (non-blocking) | | skill | Skill file changes |

PostCompact Matchers

| Matcher | Trigger | | -------- | --------------------------------------------------- | | manual | After /compact command | | auto | After auto-compact when the context window is full |

Elicitation / ElicitationResult Matchers

Matched against the MCP server name (the server requesting or receiving user input).

Notification Matchers

| Matcher | Trigger | | -------------------- | ------------------------------------ | | permission_prompt | Permission requests from Claude | | idle_prompt | Claude waiting for input (60s+ idle) | | auth_success | Authentication success | | elicitation_dialog | MCP tool elicitation |

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Important Hook Events

Setup Hook

Runs when Claude Code is invoked with repository setup and maintenance flags (--init, --init-only, or --maintenance).

Use Setup hooks for:

• One-time or occasional operations (dependency installation, migrations, cleanup)
• Operations you don't want on every session start

Key characteristics:

• Requires explicit flags because running automatically would slow down every session start
• Has access to CLAUDE_ENV_FILE for persisting environment variables
• Output added to Claude's context

SessionStart Hook

Runs when Claude Code starts a new session or resumes an existing session.

Use SessionStart hooks for:

• Loading development context (existing issues, recent changes)
• Setting up environment variables

Important: For one-time operations like installing dependencies or running migrations, use Setup hooks instead. SessionStart runs on every session, so keep these hooks fast.

PostToolUseFailure Hook

Runs immediately after a tool fails (returns an error). This complements PostToolUse, which only runs on successful tool execution.

Use PostToolUseFailure hooks for:

• Error recovery actions
• Logging tool failures
• Custom error handling and reporting

Recognizes the same matcher values as PreToolUse and PostToolUse.

SubagentStart Hook

Runs when a Claude Code subagent (Agent tool call) is spawned.

Use SubagentStart hooks for:

• Subagent initialization
• Logging subagent creation
• Context injection for specific agent types

Input includes:

• agent_id: Unique identifier for the subagent
• agent_type: Agent name (built-in like "Bash", "Explore", "Plan", or custom agent names)

For the defer permissionDecision and its constraints, see the hooks-guide reference.

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Environment Variables

| Variable | Description | Available In | | -------------------- | ---------------------------------- | ------------------- | | CLAUDE_PROJECT_DIR | Project root (absolute path) | All hooks | | CLAUDE_CODE_REMOTE | "true" if remote, empty if local | All hooks | | CLAUDE_ENV_FILE | Path for persisting env vars | SessionStart, Setup, CwdChanged, FileChanged | | CLAUDE_PLUGIN_ROOT | Plugin directory (absolute) | Plugin hooks |

SessionStart Environment Persistence

Example: Setting individual 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' >> "$CLAUDE_ENV_FILE"
  echo 'export PATH="$PATH:./node_modules/.bin"' >> "$CLAUDE_ENV_FILE"
fi
exit 0

Example: Persisting all environment changes (e.g., nvm use)

#!/bin/bash
ENV_BEFORE=$(export -p | sort)

# Run setup commands that modify environment
source ~/.nvm/nvm.sh
nvm use 20

if [ -n "$CLAUDE_ENV_FILE" ]; then
  ENV_AFTER=$(export -p | sort)
  comm -13 <(echo "$ENV_BEFORE") <(echo "$ENV_AFTER") >> "$CLAUDE_ENV_FILE"
fi
exit 0

Variables in $CLAUDE_ENV_FILE are sourced before each Bash command.

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Working with MCP Tools

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

• 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

{
  "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"
          }
        ]
      }
    ]
  }
}

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Execution Details

| Aspect | Behavior | | ------------------- | --------------------------------------- | | Timeout | 600 seconds default for commands, 30s for prompts, 60s for agent hooks, configurable | | Parallelization | All matching hooks run in parallel | | Deduplication | Identical commands deduplicated | | Environment | Runs in cwd with Claude Code's env | | Hook order | Hooks from all sources execute together |

Output Handling by Event

| Event | stdout Handling | | ---------------------------------------------------------- | -------------------------------- | | UserPromptSubmit, SessionStart, Setup | Added to Claude's context | | PreToolUse, PostToolUse, Stop | Shown in verbose mode (Ctrl+O) | | Notification, SessionEnd, SubagentStart, InstructionsLoaded | Logged to debug only (--debug) | | PostCompact | Logged to debug only (--debug) | | TeammateIdle, TaskCompleted, ConfigChange | Shown in verbose mode (Ctrl+O) | | WorktreeCreate | Stdout must be the absolute path to the created worktree directory | | WorktreeRemove | Non-blocking; logged to debug | | CwdChanged, FileChanged | Non-blocking; logged to debug | | PermissionDenied | Logged to debug only (--debug) | | Elicitation, ElicitationResult | JSON response controls MCP input |

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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
• You should thoroughly test hooks in a safe environment before production use

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 via the $CLAUDE_PROJECT_DIR variable - Specify full paths for scripts (use $CLAUDE_PROJECT_DIR)
5. Skip sensitive files - Avoid .env, .git/, keys, etc.

Configuration Safety

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

1. Hooks snapshot captured at startup
2. Snapshot used 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.

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Debugging

Enable Debug Mode

claude --debug
claude --debug "hooks"  # Filter to hooks only

Debug Output Example

[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 600000ms
[DEBUG] Hook command completed with status 0: <Your stdout>

Basic Troubleshooting

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
6. Validate plugin hooks - Use claude plugin validate or /plugin validate for plugin-level hooks

Common Issues

| Problem | Cause | Fix | | -------------------- | -------------------------------- | ---------------------------------------- | | Hook not running | Wrong matcher pattern | Check case-sensitivity, regex | | Command not found | Relative path | Use $CLAUDE_PROJECT_DIR | | JSON not processed | Non-zero exit code | Exit 0 for JSON processing | | Hook times out | Slow script | Optimize or increase timeout | | Quotes breaking | Unescaped in JSON | Use \" inside JSON strings | | Plugin hook not load | Invalid plugin.json hooks config | Validate with claude plugin validate . | | Path not found | Missing ${CLAUDE_PLUGIN_ROOT} | Use variable for plugin scripts |

Validation Commands

For plugin hooks:

# CLI (from terminal)
claude plugin validate .
claude plugin validate ./path/to/plugin

# In Claude Code session
/plugin validate .
/plugin validate ./path/to/plugin

For settings hooks: JSON validation with:

python3 -m json.tool .claude/settings.json

Test Commands Manually

echo '{"tool_name":"Write","tool_input":{"file_path":"test.txt"}}' | ./your-hook.sh

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Sources

• Hooks Reference (accessed 2026-04-23, updated from 2026-01-28)
• Hooks Guide
• Settings Reference
• Plugin Components Reference