Hooks
Customize and extend Claude Code’s behavior by registering shell commands
Introduction
Claude Code hooks are user-defined shell commands that execute at various points in Claude Code’s lifecycle. Hooks provide deterministic control over Claude Code’s behavior, ensuring certain actions always happen rather than relying on the LLM to choose to run them.
Example use cases include:
- Notifications: Customize how you get notified when Claude Code is awaiting your input or permission to run something.
- Automatic formatting: Run
prettier
on .ts files,gofmt
on .go files, etc. after every file edit. - Logging: Track and count all executed commands for compliance or debugging.
- Feedback: Provide automated feedback when Claude Code produces code that does not follow your codebase conventions.
- Custom permissions: Block modifications to production files or sensitive directories.
By encoding these rules as hooks rather than prompting instructions, you turn suggestions into app-level code that executes every time it is expected to run.
Hooks execute shell commands with your full user permissions without confirmation. You are responsible for ensuring your hooks are safe and secure. Anthropic is not liable for any data loss or system damage resulting from hook usage. Review Security Considerations.
Quickstart
In this quickstart, you’ll add a hook that logs the shell commands that Claude Code runs.
Quickstart Prerequisite: Install jq
for JSON processing in the command line.
Step 1: Open hooks configuration
Run the /hooks
slash command and select
the PreToolUse
hook event.
PreToolUse
hooks run before tool calls and can block them while providing
Claude feedback on what to do differently.
Step 2: Add a matcher
Select + Add new matcher…
to run your hook only on Bash tool calls.
Type Bash
for the matcher.
Step 3: Add the hook
Select + Add new hook…
and enter this command:
Step 4: Save your configuration
For storage location, select User settings
since you’re logging to your home
directory. This hook will then apply to all projects, not just your current
project.
Then press Esc until you return to the REPL. Your hook is now registered!
Step 5: Verify your hook
Run /hooks
again or check ~/.claude/settings.json
to see your configuration:
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:
- matcher: Pattern to match tool names (only applicable for
PreToolUse
andPostToolUse
)- Simple strings match exactly:
Write
matches only the Write tool - Supports regex:
Edit|Write
orNotebook.*
- If omitted or empty string, hooks run for all matching events
- Simple strings match exactly:
- hooks: Array of commands to execute when the pattern matches
type
: Currently only"command"
is supportedcommand
: The bash command to execute
Hook Events
PreToolUse
Runs after Claude creates tool parameters and before processing the tool call.
Common matchers:
Task
- Agent tasksBash
- Shell commandsGlob
- File pattern matchingGrep
- Content searchRead
- File readingEdit
,MultiEdit
- File editingWrite
- File writingWebFetch
,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.
Stop
Runs when Claude Code has finished responding.
Hook Input
Hooks receive JSON data via stdin containing session information and event-specific data:
PreToolUse Input
The exact schema for tool_input
depends on the tool.
PostToolUse Input
The exact schema for tool_input
and tool_response
depends on the tool.
Notification Input
Stop 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.
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). - 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.
Exit Code 2 Behavior
Hook Event | Behavior |
---|---|
PreToolUse | Blocks the tool call, shows error to Claude |
PostToolUse | Shows error to Claude (tool already ran) |
Notification | N/A, shows stderr to user only |
Stop | Blocks stoppage, shows error to Claude |
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:
If continue
is false, Claude stops processing after the hooks run.
- For
PreToolUse
, this is different from"decision": "block"
, 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
Stop
, 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.
- “approve” bypasses the permission system.
reason
is shown to the user but not to Claude. - “block” prevents the tool call from executing.
reason
is shown to Claude. undefined
leads to the existing permission flow.reason
is ignored.
PostToolUse
Decision Control
PostToolUse
hooks can control whether a tool call proceeds.
- “block” automatically prompts Claude with
reason
. undefined
does nothing.reason
is ignored.
Stop
Decision Control
Stop
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.
JSON Output Example: Bash Command Editing
Stop
Decision Control
Stop
hooks can control tool execution:
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 toolmcp__filesystem__read_file
- Filesystem server’s read file toolmcp__github__search_repositories
- GitHub server’s search tool
Configuring Hooks for MCP Tools
You can target specific MCP tools or entire MCP servers:
Examples
Code Formatting
Automatically format code after file modifications:
Notification
Customize the notification that is sent when Claude Code requests permission or when the prompt input has become idle.
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:
- Validate and sanitize inputs - Never trust input data blindly
- Always quote shell variables - Use
"$VAR"
not$VAR
- Block path traversal - Check for
..
in file paths - Use absolute paths - Specify full paths for scripts
- Skip sensitive files - Avoid
.env
,.git/
, keys, etc.
Configuration Safety
Direct edits to hooks in settings files don’t take effect immediately. Claude Code:
- Captures a snapshot of hooks at startup
- Uses this snapshot throughout the session
- Warns if hooks are modified externally
- 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
- Parallelization: All matching hooks run in parallel
- Environment: Runs in current directory with Claude Code’s environment
- Input: JSON via stdin
- Output:
- PreToolUse/PostToolUse/Stop: Progress shown in transcript (Ctrl-R)
- Notification: Logged to debug only (
--debug
)
Debugging
To troubleshoot hooks:
- Check if
/hooks
menu displays your configuration - Verify that your settings files are valid JSON
- Test commands manually
- Check exit codes
- Review stdout and stderr format expectations
- Ensure proper quote escaping
Progress messages appear in transcript mode (Ctrl-R) showing:
- Which hook is running
- Command being executed
- Success/failure status
- Output or error messages