create-hook

name	create-hook
description	Create and configure git hooks with intelligent project analysis, suggestions, and automated testing
argument-hint	Optional hook type or description of desired behavior

Create Hook Command

Analyze the project, suggest practical hooks, and create them with proper testing.

Your Task (/create-hook)

1. Analyze environment - Detect tooling and existing hooks
2. Suggest hooks - Based on your project configuration
3. Configure hook - Ask targeted questions and create the script
4. Test & validate - Ensure the hook works correctly

Your Workflow

1. Environment Analysis & Suggestions

Automatically detect the project tooling and suggest relevant hooks:

When TypeScript is detected (tsconfig.json):

• PostToolUse hook: "Type-check files after editing"
• PreToolUse hook: "Block edits with type errors"

When Prettier is detected (.prettierrc, prettier.config.js):

• PostToolUse hook: "Auto-format files after editing"
• PreToolUse hook: "Require formatted code"

When ESLint is detected (.eslintrc.*):

• PostToolUse hook: "Lint and auto-fix after editing"
• PreToolUse hook: "Block commits with linting errors"

When package.json has scripts:

• test script → "Run tests before commits"
• build script → "Validate build before commits"

When a git repository is detected:

• PreToolUse/Bash hook: "Prevent commits with secrets"
• PostToolUse hook: "Security scan on file changes"

Decision Tree:

Project has TypeScript? → Suggest type checking hooks
Project has formatter? → Suggest formatting hooks
Project has tests? → Suggest test validation hooks
Security sensitive? → Suggest security hooks
+ Scan for additional patterns and suggest custom hooks based on:
  - Custom scripts in package.json
  - Unique file patterns or extensions
  - Development workflow indicators
  - Project-specific tooling configurations

2. Hook Configuration

Start by asking: "What should this hook do?" and offer relevant suggestions from your analysis.

Then understand the context from the user's description and only ask about details you're unsure about:

1. Trigger timing: When should it run?

   • PreToolUse: Before file operations (can block)
   • PostToolUse: After file operations (feedback/fixes)
   • UserPromptSubmit: Before processing requests
   • Other event types as needed

2. Tool matcher: Which tools should trigger it? (Write, Edit, Bash, * etc)

3. Scope: global, project, or project-local

4. Response approach:

   • Exit codes only: Simple (exit 0 = success, exit 2 = block in PreToolUse)
   • JSON response: Advanced control (blocking, context, decisions)
   • Guide based on complexity: simple pass/fail → exit codes, rich feedback → JSON

5. Blocking behavior (if relevant): "Should this stop operations when issues are found?"

   • PreToolUse: Can block operations (security, validation)
   • PostToolUse: Usually provide feedback only

6. Claude integration (CRITICAL): "Should Claude Code automatically see and fix issues this hook detects?"

   • If YES: Use additionalContext for error communication
   • If NO: Use suppressOutput: true for silent operation

7. Context pollution: "Should successful operations be silent to avoid noise?"

   • Recommend YES for formatting, routine checks
   • Recommend NO for security alerts, critical errors

8. File filtering: "What file types should this hook process?"

3. Hook Creation

You should:

• Create hooks directory: ~/.claude/hooks/ or .claude/hooks/ based on scope
• Generate script: Create hook script with:
  • Proper shebang and executable permissions
  • Project-specific commands (use detected config paths)
  • Comments explaining the hook's purpose
• Update settings: Add hook configuration to appropriate settings.json
• Use absolute paths: Avoid relative paths to scripts and executables. Use $CLAUDE_PROJECT_DIR to reference project root
• Offer validation: Ask if the user wants you to test the hook

Key Implementation Standards:

• Read JSON from stdin (never use argv)
• Use top-level additionalContext/systemMessage for Claude communication
• Include suppressOutput: true for successful operations
• Provide specific error counts and actionable feedback
• Focus on changed files rather than entire codebase
• Support common development workflows

⚠️ CRITICAL: Input/Output Format

This is where most hook implementations fail. Pay extra attention to:

• Input: Reading JSON from stdin correctly (not argv)
• Output: Using correct top-level JSON structure for Claude communication
• Documentation: Consulting official docs for exact schemas when in doubt

4. Testing & Validation

CRITICAL: Test both happy and sad paths:

Happy Path Testing:

1. Test expected success scenario - Create conditions where hook should pass
   • Examples: TypeScript (valid code), Linting (formatted code), Security (safe commands)

Sad Path Testing: 2. Test expected failure scenario - Create conditions where hook should fail/warn

• Examples: TypeScript (type errors), Linting (unformatted code), Security (dangerous operations)

Verification Steps: 3. Verify expected behavior: Check if it blocks/warns/provides context as intended

Example Testing Process:

• For a hook preventing file deletion: Create a test file, attempt the protected action, and verify the hook prevents it

If Issues Occur, you should:

• Check hook registration in settings
• Verify script permissions (chmod +x)
• Test with simplified version first
• Debug with detailed hook execution analysis

Hook Templates

Type Checking (PostToolUse)

#!/usr/bin/env node
// Read stdin JSON, check .ts/.tsx files only
// Run: npx tsc --noEmit --pretty
// Output: JSON with additionalContext for errors

Auto-formatting (PostToolUse)

#!/usr/bin/env node
// Read stdin JSON, check supported file types
// Run: npx prettier --write [file]
// Output: JSON with suppressOutput: true

Security Scanning (PreToolUse)

#!/bin/bash
# Read stdin JSON, check for secrets/keys
# Block if dangerous patterns found
# Exit 2 to block, 0 to continue

Complete templates available at: https://docs.claude.com/en/docs/claude-code/hooks#examples

Quick Reference

📖 Official Docs: https://docs.claude.com/en/docs/claude-code/hooks.md

Common Patterns:

• stdin input: JSON.parse(process.stdin.read())
• File filtering: Check extensions before processing
• Success response: {continue: true, suppressOutput: true}
• Error response: {continue: true, additionalContext: "error details"}
• Block operation: exit(2) in PreToolUse hooks

Hook Types by Use Case:

• Code Quality: PostToolUse for feedback and fixes
• Security: PreToolUse to block dangerous operations
• CI/CD: PreToolUse to validate before commits
• Development: PostToolUse for automated improvements

Hook Execution Best Practices:

• Hooks run in parallel according to official documentation
• Design for independence since execution order isn't guaranteed
• Plan hook interactions carefully when multiple hooks affect the same files

Success Criteria

✅ Hook created successfully when:

• Script has executable permissions
• Registered in correct settings.json
• Responds correctly to test scenarios
• Integrates properly with Claude for automated fixes
• Follows project conventions and detected tooling

Result: The user gets a working hook that enhances their development workflow with intelligent automation and quality checks.

---

Documentation Index

Fetch the complete documentation index at: https://code.claude.com/docs/llms.txt Use this file to discover all available pages before exploring further.

Automate workflows with hooks

Run shell commands automatically when Claude Code edits files, finishes tasks, or needs input. Format code, send notifications, validate commands, and enforce project rules.

Hooks are user-defined shell commands that execute at specific points in Claude Code's lifecycle. They provide deterministic control over Claude Code's behavior, ensuring certain actions always happen rather than relying on the LLM to choose to run them. Use hooks to enforce project rules, automate repetitive tasks, and integrate Claude Code with your existing tools.

For decisions that require judgment rather than deterministic rules, you can also use prompt-based hooks or agent-based hooks that use a Claude model to evaluate conditions.

For other ways to extend Claude Code, see skills for giving Claude additional instructions and executable commands, subagents for running tasks in isolated contexts, and plugins for packaging extensions to share across projects.

This guide covers common use cases and how to get started. For full event schemas, JSON input/output formats, and advanced features like async hooks and MCP tool hooks, see the [Hooks reference](/en/hooks).

Set up your first hook

The fastest way to create a hook is through the /hooks interactive menu in Claude Code. This walkthrough creates a desktop notification hook, so you get alerted whenever Claude is waiting for your input instead of watching the terminal.

Type `/hooks` in the Claude Code CLI. You'll see a list of all available hook events, plus an option to disable all hooks. Each event corresponds to a point in Claude's lifecycle where you can run custom code. Select `Notification` to create a hook that fires when Claude needs your attention. The menu shows a list of matchers, which filter when the hook fires. Set the matcher to `*` to fire on all notification types. You can narrow it later by changing the matcher to a specific value like `permission_prompt` or `idle_prompt`. Select `+ Add new hook…`. The menu prompts you for a shell command to run when the event fires. Hooks run any shell command you provide, so you can use your platform's built-in notification tool. Copy the command for your OS:

<Tabs>
  <Tab title="macOS">
    Uses [`osascript`](https://ss64.com/mac/osascript.html) to trigger a native macOS notification through AppleScript:

    ```
    osascript -e 'display notification "Claude Code needs your attention" with title "Claude Code"'
    ```
  </Tab>

  <Tab title="Linux">
    Uses `notify-send`, which is pre-installed on most Linux desktops with a notification daemon:

    ```
    notify-send 'Claude Code' 'Claude Code needs your attention'
    ```
  </Tab>

  <Tab title="Windows (PowerShell)">
    Uses PowerShell to show a native message box through .NET's Windows Forms:

    ```
    powershell.exe -Command "[System.Reflection.Assembly]::LoadWithPartialName('System.Windows.Forms'); [System.Windows.Forms.MessageBox]::Show('Claude Code needs your attention', 'Claude Code')"
    ```
  </Tab>
</Tabs>

The menu asks where to save the hook configuration. Select `User settings` to store it in `~/.claude/settings.json`, which applies the hook to all your projects. You could also choose `Project settings` to scope it to the current project. See [Configure hook location](#configure-hook-location) for all available scopes. Press `Esc` to return to the CLI. Ask Claude to do something that requires permission, then switch away from the terminal. You should receive a desktop notification.

What you can automate

Hooks let you run code at key points in Claude Code's lifecycle: format files after edits, block commands before they execute, send notifications when Claude needs input, inject context at session start, and more. For the full list of hook events, see the Hooks reference.

Each example includes a ready-to-use configuration block that you add to a settings file. The most common patterns:

• Get notified when Claude needs input
• Auto-format code after edits
• Block edits to protected files
• Re-inject context after compaction

Get notified when Claude needs input

Get a desktop notification whenever Claude finishes working and needs your input, so you can switch to other tasks without checking the terminal.

This hook uses the Notification event, which fires when Claude is waiting for input or permission. Each tab below uses the platform's native notification command. Add this to ~/.claude/settings.json, or use the interactive walkthrough above to configure it with /hooks:

```json theme={null} { "hooks": { "Notification": [ { "matcher": "", "hooks": [ { "type": "command", "command": "osascript -e 'display notification \"Claude Code needs your attention\" with title \"Claude Code\"'" } ] } ] } } ``` ```json theme={null} { "hooks": { "Notification": [ { "matcher": "", "hooks": [ { "type": "command", "command": "notify-send 'Claude Code' 'Claude Code needs your attention'" } ] } ] } } ``` ```json theme={null} { "hooks": { "Notification": [ { "matcher": "", "hooks": [ { "type": "command", "command": "powershell.exe -Command \"[System.Reflection.Assembly]::LoadWithPartialName('System.Windows.Forms'); [System.Windows.Forms.MessageBox]::Show('Claude Code needs your attention', 'Claude Code')\"" } ] } ] } } ```

Auto-format code after edits

Automatically run Prettier on every file Claude edits, so formatting stays consistent without manual intervention.

This hook uses the PostToolUse event with an Edit|Write matcher, so it runs only after file-editing tools. The command extracts the edited file path with jq and passes it to Prettier. Add this to .claude/settings.json in your project root:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          {
            "type": "command",
            "command": "jq -r '.tool_input.file_path' | xargs npx prettier --write"
          }
        ]
      }
    ]
  }
}

The Bash examples on this page use `jq` for JSON parsing. Install it with `brew install jq` (macOS), `apt-get install jq` (Debian/Ubuntu), or see [`jq` downloads](https://jqlang.github.io/jq/download/).

Block edits to protected files

Prevent Claude from modifying sensitive files like .env, package-lock.json, or anything in .git/. Claude receives feedback explaining why the edit was blocked, so it can adjust its approach.

This example uses a separate script file that the hook calls. The script checks the target file path against a list of protected patterns and exits with code 2 to block the edit.

Save this to `.claude/hooks/protect-files.sh`:

```bash  theme={null}
#!/bin/bash
# protect-files.sh

INPUT=$(cat)
FILE_PATH=$(echo "$INPUT" | jq -r '.tool_input.file_path // empty')

PROTECTED_PATTERNS=(".env" "package-lock.json" ".git/")

for pattern in "${PROTECTED_PATTERNS[@]}"; do
  if [[ "$FILE_PATH" == *"$pattern"* ]]; then
    echo "Blocked: $FILE_PATH matches protected pattern '$pattern'" >&2
    exit 2
  fi
done

exit 0
```

Hook scripts must be executable for Claude Code to run them:

```bash  theme={null}
chmod +x .claude/hooks/protect-files.sh
```

Add a `PreToolUse` hook to `.claude/settings.json` that runs the script before any `Edit` or `Write` tool call:

```json  theme={null}
{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          {
            "type": "command",
            "command": "\"$CLAUDE_PROJECT_DIR\"/.claude/hooks/protect-files.sh"
          }
        ]
      }
    ]
  }
}
```

Re-inject context after compaction

When Claude's context window fills up, compaction summarizes the conversation to free space. This can lose important details. Use a SessionStart hook with a compact matcher to re-inject critical context after every compaction.

Any text your command writes to stdout is added to Claude's context. This example reminds Claude of project conventions and recent work. Add this to .claude/settings.json in your project root:

{
  "hooks": {
    "SessionStart": [
      {
        "matcher": "compact",
        "hooks": [
          {
            "type": "command",
            "command": "echo 'Reminder: use Bun, not npm. Run bun test before committing. Current sprint: auth refactor.'"
          }
        ]
      }
    ]
  }
}

You can replace the echo with any command that produces dynamic output, like git log --oneline -5 to show recent commits. For injecting context on every session start, consider using CLAUDE.md instead. For environment variables, see CLAUDE_ENV_FILE in the reference.

How hooks work

Hook events fire at specific lifecycle points in Claude Code. When an event fires, all matching hooks run in parallel, and identical hook commands are automatically deduplicated. The table below shows each event and when it triggers:

Event	When it fires
SessionStart	When a session begins or resumes
UserPromptSubmit	When you submit a prompt, before Claude processes it
PreToolUse	Before a tool call executes. Can block it
PermissionRequest	When a permission dialog appears
PostToolUse	After a tool call succeeds
PostToolUseFailure	After a tool call fails
Notification	When Claude Code sends a notification
SubagentStart	When a subagent is spawned
SubagentStop	When a subagent finishes
Stop	When Claude finishes responding
PreCompact	Before context compaction
SessionEnd	When a session terminates

Each hook has a type that determines how it runs. Most hooks use "type": "command", which runs a shell command. Two other options use a Claude model to make decisions: "type": "prompt" for single-turn evaluation and "type": "agent" for multi-turn verification with tool access. See Prompt-based hooks and Agent-based hooks for details.

Read input and return output

Hooks communicate with Claude Code through stdin, stdout, stderr, and exit codes. When an event fires, Claude Code passes event-specific data as JSON to your script's stdin. Your script reads that data, does its work, and tells Claude Code what to do next via the exit code.

Hook input

Every event includes common fields like session_id and cwd, but each event type adds different data. For example, when Claude runs a Bash command, a PreToolUse hook receives something like this on stdin:

{
  "session_id": "abc123",          // unique ID for this session
  "cwd": "/Users/sarah/myproject", // working directory when the event fired
  "hook_event_name": "PreToolUse", // which event triggered this hook
  "tool_name": "Bash",             // the tool Claude is about to use
  "tool_input": {                  // the arguments Claude passed to the tool
    "command": "npm test"          // for Bash, this is the shell command
  }
}

Your script can parse that JSON and act on any of those fields. UserPromptSubmit hooks get the prompt text instead, SessionStart hooks get the source (startup, resume, compact), and so on. See Common input fields in the reference for shared fields, and each event's section for event-specific schemas.

Hook output

Your script tells Claude Code what to do next by writing to stdout or stderr and exiting with a specific code. For example, a PreToolUse hook that wants to block a command:

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

if echo "$COMMAND" | grep -q "drop table"; then
  echo "Blocked: dropping tables is not allowed" >&2  # stderr becomes Claude's feedback
  exit 2                                               # exit 2 = block the action
fi

exit 0  # exit 0 = let it proceed

The exit code determines what happens next:

• Exit 0: the action proceeds. For UserPromptSubmit and SessionStart hooks, anything you write to stdout is added to Claude's context.
• Exit 2: the action is blocked. Write a reason to stderr, and Claude receives it as feedback so it can adjust.
• Any other exit code: the action proceeds. Stderr is logged but not shown to Claude. Toggle verbose mode with Ctrl+O to see these messages in the transcript.

Structured JSON output

Exit codes give you two options: allow or block. For more control, exit 0 and print a JSON object to stdout instead.

Use exit 2 to block with a stderr message, or exit 0 with JSON for structured control. Don't mix them: Claude Code ignores JSON when you exit 2.

For example, a PreToolUse hook can deny a tool call and tell Claude why, or escalate it to the user for approval:

{
  "hookSpecificOutput": {
    "hookEventName": "PreToolUse",
    "permissionDecision": "deny",
    "permissionDecisionReason": "Use rg instead of grep for better performance"
  }
}

Claude Code reads permissionDecision and cancels the tool call, then feeds permissionDecisionReason back to Claude as feedback. These three options are specific to PreToolUse:

• "allow": proceed without showing a permission prompt
• "deny": cancel the tool call and send the reason to Claude
• "ask": show the permission prompt to the user as normal

Other events use different decision patterns. For example, PostToolUse and Stop hooks use a top-level decision: "block" field, while PermissionRequest uses hookSpecificOutput.decision.behavior. See the summary table in the reference for a full breakdown by event.

For UserPromptSubmit hooks, use additionalContext instead to inject text into Claude's context. Prompt-based hooks (type: "prompt") handle output differently: see Prompt-based hooks.

Filter hooks with matchers

Without a matcher, a hook fires on every occurrence of its event. Matchers let you narrow that down. For example, if you want to run a formatter only after file edits (not after every tool call), add a matcher to your PostToolUse hook:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          { "type": "command", "command": "prettier --write ..." }
        ]
      }
    ]
  }
}

The "Edit|Write" matcher is a regex pattern that matches the tool name. The hook only fires when Claude uses the Edit or Write tool, not when it uses Bash, Read, or any other tool.

Each event type matches on a specific field. Matchers support exact strings and regex patterns:

Event	What the matcher filters	Example matcher values
PreToolUse, PostToolUse, PostToolUseFailure, PermissionRequest	tool name	Bash, Edit|Write, mcp__.*
SessionStart	how the session started	startup, resume, clear, compact
SessionEnd	why the session ended	clear, logout, prompt_input_exit, other
Notification	notification type	permission_prompt, idle_prompt, auth_success, elicitation_dialog
SubagentStart	agent type	Bash, Explore, Plan, or custom agent names
PreCompact	what triggered compaction	manual, auto
UserPromptSubmit, Stop	no matcher support	always fires on every occurrence
SubagentStop	agent type	same values as SubagentStart

A few more examples showing matchers on different event types:

Match only `Bash` tool calls and log each command to a file. The `PostToolUse` event fires after the command completes, so `tool_input.command` contains what ran. The hook receives the event data as JSON on stdin, and `jq -r '.tool_input.command'` extracts just the command string, which `>>` appends to the log file:

```json  theme={null}
{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Bash",
        "hooks": [
          {
            "type": "command",
            "command": "jq -r '.tool_input.command' >> ~/.claude/command-log.txt"
          }
        ]
      }
    ]
  }
}
```

MCP tools use a different naming convention than built-in tools: `mcp____`, where `` is the MCP server name and `` is the tool it provides. For example, `mcp__github__search_repositories` or `mcp__filesystem__read_file`. Use a regex matcher to target all tools from a specific server, or match across servers with a pattern like `mcp__.*__write.*`. See [Match MCP tools](/en/hooks#match-mcp-tools) in the reference for the full list of examples.

The command below extracts the tool name from the hook's JSON input with `jq` and writes it to stderr, where it shows up in verbose mode (`Ctrl+O`):

```json  theme={null}
{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "mcp__github__.*",
        "hooks": [
          {
            "type": "command",
            "command": "echo \"GitHub tool called: $(jq -r '.tool_name')\" >&2"
          }
        ]
      }
    ]
  }
}
```

The `SessionEnd` event supports matchers on the reason the session ended. This hook only fires on `clear` (when you run `/clear`), not on normal exits:

```json  theme={null}
{
  "hooks": {
    "SessionEnd": [
      {
        "matcher": "clear",
        "hooks": [
          {
            "type": "command",
            "command": "rm -f /tmp/claude-scratch-*.txt"
          }
        ]
      }
    ]
  }
}
```

For full matcher syntax, see the Hooks reference.

Configure hook location

Where you add a hook determines its scope:

Location	Scope	Shareable
~/.claude/settings.json	All your projects	No, local to your machine
.claude/settings.json	Single project	Yes, can be committed to the repo
.claude/settings.local.json	Single project	No, gitignored
Managed policy settings	Organization-wide	Yes, admin-controlled
Plugin hooks/hooks.json	When plugin is enabled	Yes, bundled with the plugin
Skill or agent frontmatter	While the skill or agent is active	Yes, defined in the component file

You can also use the /hooks menu in Claude Code to add, delete, and view hooks interactively. To disable all hooks at once, use the toggle at the bottom of the /hooks menu or set "disableAllHooks": true in your settings file.

Hooks added through the /hooks menu take effect immediately. If you edit settings files directly while Claude Code is running, the changes won't take effect until you review them in the /hooks menu or restart your session.

Prompt-based hooks

For decisions that require judgment rather than deterministic rules, use type: "prompt" hooks. Instead of running a shell command, Claude Code sends your prompt and the hook's input data to a Claude model (Haiku by default) to make the decision. You can specify a different model with the model field if you need more capability.

The model's only job is to return a yes/no decision as JSON:

• "ok": true: the action proceeds
• "ok": false: the action is blocked. The model's "reason" is fed back to Claude so it can adjust.

This example uses a Stop hook to ask the model whether all requested tasks are complete. If the model returns "ok": false, Claude keeps working and uses the reason as its next instruction:

{
  "hooks": {
    "Stop": [
      {
        "hooks": [
          {
            "type": "prompt",
            "prompt": "Check if all tasks are complete. If not, respond with {\"ok\": false, \"reason\": \"what remains to be done\"}."
          }
        ]
      }
    ]
  }
}

For full configuration options, see Prompt-based hooks in the reference.

Agent-based hooks

When verification requires inspecting files or running commands, use type: "agent" hooks. Unlike prompt hooks which make a single LLM call, agent hooks spawn a subagent that can read files, search code, and use other tools to verify conditions before returning a decision.

Agent hooks use the same "ok" / "reason" response format as prompt hooks, but with a longer default timeout of 60 seconds and up to 50 tool-use turns.

This example verifies that tests pass before allowing Claude to stop:

{
  "hooks": {
    "Stop": [
      {
        "hooks": [
          {
            "type": "agent",
            "prompt": "Verify that all unit tests pass. Run the test suite and check the results. $ARGUMENTS",
            "timeout": 120
          }
        ]
      }
    ]
  }
}

Use prompt hooks when the hook input data alone is enough to make a decision. Use agent hooks when you need to verify something against the actual state of the codebase.

For full configuration options, see Agent-based hooks in the reference.

Limitations and troubleshooting

Limitations

• Hooks communicate through stdout, stderr, and exit codes only. They cannot trigger slash commands or tool calls directly.
• Hook timeout is 10 minutes by default, configurable per hook with the timeout field (in seconds).
• PostToolUse hooks cannot undo actions since the tool has already executed.
• PermissionRequest hooks do not fire in non-interactive mode (-p). Use PreToolUse hooks for automated permission decisions.
• Stop hooks fire whenever Claude finishes responding, not only at task completion. They do not fire on user interrupts.

Hook not firing

The hook is configured but never executes.

• Run /hooks and confirm the hook appears under the correct event
• Check that the matcher pattern matches the tool name exactly (matchers are case-sensitive)
• Verify you're triggering the right event type (e.g., PreToolUse fires before tool execution, PostToolUse fires after)
• If using PermissionRequest hooks in non-interactive mode (-p), switch to PreToolUse instead

Hook error in output

You see a message like "PreToolUse hook error: ..." in the transcript.

• Your script exited with a non-zero code unexpectedly. Test it manually by piping sample JSON:

  echo '{"tool_name":"Bash","tool_input":{"command":"ls"}}' | ./my-hook.sh
  echo $?  # Check the exit code
  

• If you see "command not found", use absolute paths or $CLAUDE_PROJECT_DIR to reference scripts

• If you see "jq: command not found", install jq or use Python/Node.js for JSON parsing
• If the script isn't running at all, make it executable: chmod +x ./my-hook.sh

/hooks shows no hooks configured

You edited a settings file but the hooks don't appear in the menu.

• Restart your session or open /hooks to reload. Hooks added through the /hooks menu take effect immediately, but manual file edits require a reload.
• Verify your JSON is valid (trailing commas and comments are not allowed)
• Confirm the settings file is in the correct location: .claude/settings.json for project hooks, ~/.claude/settings.json for global hooks

Stop hook runs forever

Claude keeps working in an infinite loop instead of stopping.

Your Stop hook script needs to check whether it already triggered a continuation. Parse the stop_hook_active field from the JSON input and exit early if it's true:

#!/bin/bash
INPUT=$(cat)
if [ "$(echo "$INPUT" | jq -r '.stop_hook_active')" = "true" ]; then
  exit 0  # Allow Claude to stop
fi
# ... rest of your hook logic

JSON validation failed

Claude Code shows a JSON parsing error even though your hook script outputs valid JSON.

When Claude Code runs a hook, it spawns a shell that sources your profile (~/.zshrc or ~/.bashrc). If your profile contains unconditional echo statements, that output gets prepended to your hook's JSON:

Shell ready on arm64
{"decision": "block", "reason": "Not allowed"}

Claude Code tries to parse this as JSON and fails. To fix this, wrap echo statements in your shell profile so they only run in interactive shells:

# In ~/.zshrc or ~/.bashrc
if [[ $- == *i* ]]; then
  echo "Shell ready"
fi

The $- variable contains shell flags, and i means interactive. Hooks run in non-interactive shells, so the echo is skipped.

Debug techniques

Toggle verbose mode with Ctrl+O to see hook output in the transcript, or run claude --debug for full execution details including which hooks matched and their exit codes.

Learn more

• Hooks reference: full event schemas, JSON output format, async hooks, and MCP tool hooks
• Security considerations: review before deploying hooks in shared or production environments
• Bash command validator example: complete reference implementation

---

Documentation Index

Fetch the complete documentation index at: https://code.claude.com/docs/llms.txt Use this file to discover all available pages before exploring further.

Hooks reference

Reference for Claude Code hook events, configuration schema, JSON input/output formats, exit codes, async hooks, prompt hooks, and MCP tool hooks.

For a quickstart guide with examples, see [Automate workflows with hooks](/en/hooks-guide).

Hooks are user-defined shell commands or LLM prompts that execute automatically at specific points in Claude Code's lifecycle. Use this reference to look up event schemas, configuration options, JSON input/output formats, and advanced features like async hooks and MCP tool hooks. If you're setting up hooks for the first time, start with the guide instead.

Hook lifecycle

Hooks fire at specific points during a Claude Code session. When an event fires and a matcher matches, Claude Code passes JSON context about the event to your hook handler. For command hooks, this arrives on stdin. Your handler can then inspect the input, take action, and optionally return a decision. Some events fire once per session, while others fire repeatedly inside the agentic loop:

The table below summarizes when each event fires. The Hook events section documents the full input schema and decision control options for each one.

Event	When it fires
SessionStart	When a session begins or resumes
UserPromptSubmit	When you submit a prompt, before Claude processes it
PreToolUse	Before a tool call executes. Can block it
PermissionRequest	When a permission dialog appears
PostToolUse	After a tool call succeeds
PostToolUseFailure	After a tool call fails
Notification	When Claude Code sends a notification
SubagentStart	When a subagent is spawned
SubagentStop	When a subagent finishes
Stop	When Claude finishes responding
PreCompact	Before context compaction
SessionEnd	When a session terminates

How a hook resolves

To see how these pieces fit together, consider this PreToolUse hook that blocks destructive shell commands. The hook runs block-rm.sh before every Bash tool call:

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Bash",
        "hooks": [
          {
            "type": "command",
            "command": ".claude/hooks/block-rm.sh"
          }
        ]
      }
    ]
  }
}

The script reads the JSON input from stdin, extracts the command, and returns a permissionDecision of "deny" if it contains rm -rf:

#!/bin/bash
# .claude/hooks/block-rm.sh
COMMAND=$(jq -r '.tool_input.command')

if echo "$COMMAND" | grep -q 'rm -rf'; then
  jq -n '{
    hookSpecificOutput: {
      hookEventName: "PreToolUse",
      permissionDecision: "deny",
      permissionDecisionReason: "Destructive command blocked by hook"
    }
  }'
else
  exit 0  # allow the command
fi

Now suppose Claude Code decides to run Bash "rm -rf /tmp/build". Here's what happens:

The `PreToolUse` event fires. Claude Code sends the tool input as JSON on stdin to the hook:

```json  theme={null}
{ "tool_name": "Bash", "tool_input": { "command": "rm -rf /tmp/build" }, ... }
```

The matcher `"Bash"` matches the tool name, so `block-rm.sh` runs. If you omit the matcher or use `"*"`, the hook runs on every occurrence of the event. Hooks only skip when a matcher is defined and doesn't match. The script extracts `"rm -rf /tmp/build"` from the input and finds `rm -rf`, so it prints a decision to stdout:

```json  theme={null}
{
  "hookSpecificOutput": {
    "hookEventName": "PreToolUse",
    "permissionDecision": "deny",
    "permissionDecisionReason": "Destructive command blocked by hook"
  }
}
```

If the command had been safe (like `npm test`), the script would hit `exit 0` instead, which tells Claude Code to allow the tool call with no further action.

Claude Code reads the JSON decision, blocks the tool call, and shows Claude the reason.

The Configuration section below documents the full schema, and each hook event section documents what input your command receives and what output it can return.

Configuration

Hooks are defined in JSON settings files. The configuration has three levels of nesting:

1. Choose a hook event to respond to, like PreToolUse or Stop
2. Add a matcher group to filter when it fires, like "only for the Bash tool"
3. Define one or more hook handlers to run when matched

See How a hook resolves above for a complete walkthrough with an annotated example.

This page uses specific terms for each level: **hook event** for the lifecycle point, **matcher group** for the filter, and **hook handler** for the shell command, prompt, or agent that runs. "Hook" on its own refers to the general feature.

Hook locations

Where you define a hook determines its scope:

Location	Scope	Shareable
~/.claude/settings.json	All your projects	No, local to your machine
.claude/settings.json	Single project	Yes, can be committed to the repo
.claude/settings.local.json	Single project	No, gitignored
Managed policy settings	Organization-wide	Yes, admin-controlled
Plugin hooks/hooks.json	When plugin is enabled	Yes, bundled with the plugin
Skill or agent frontmatter	While the component is active	Yes, defined in the component file

For details on settings file resolution, see settings. Enterprise administrators can use allowManagedHooksOnly to block user, project, and plugin hooks. See Hook configuration.

Matcher patterns

The matcher field is a regex string that filters when hooks fire. Use "*", "", or omit matcher entirely to match all occurrences. Each event type matches on a different field:

Event	What the matcher filters	Example matcher values
PreToolUse, PostToolUse, PostToolUseFailure, PermissionRequest	tool name	Bash, Edit|Write, mcp__.*
SessionStart	how the session started	startup, resume, clear, compact
SessionEnd	why the session ended	clear, logout, prompt_input_exit, bypass_permissions_disabled, other
Notification	notification type	permission_prompt, idle_prompt, auth_success, elicitation_dialog
SubagentStart	agent type	Bash, Explore, Plan, or custom agent names
PreCompact	what triggered compaction	manual, auto
SubagentStop	agent type	same values as SubagentStart
UserPromptSubmit, Stop	no matcher support	always fires on every occurrence

The matcher is a regex, so Edit|Write matches either tool and Notebook.* matches any tool starting with Notebook. The matcher runs against a field from the JSON input that Claude Code sends to your hook on stdin. For tool events, that field is tool_name. Each hook event section lists the full set of matcher values and the input schema for that event.

This example runs a linting script only when Claude writes or edits a file:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          {
            "type": "command",
            "command": "/path/to/lint-check.sh"
          }
        ]
      }
    ]
  }
}

UserPromptSubmit and Stop don't support matchers and always fire on every occurrence. If you add a matcher field to these events, it is silently ignored.

Match MCP tools

MCP server tools appear as regular tools in tool events (PreToolUse, PostToolUse, PostToolUseFailure, PermissionRequest), so you can match them the same way you match any other tool name.

MCP tools follow the naming pattern mcp__<server>__<tool>, for example:

• 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

Use regex patterns to target specific MCP tools or groups of tools:

• mcp__memory__.* matches all tools from the memory server
• mcp__.*__write.* matches any tool containing "write" from any server

This example logs all memory server operations and validates write operations from any MCP server:

{
  "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"
          }
        ]
      }
    ]
  }
}

Hook handler fields

Each object in the inner hooks array is a hook handler: the shell command, LLM prompt, or agent that runs when the matcher matches. There are three types:

• Command hooks (type: "command"): run a shell command. Your script receives the event's JSON input on stdin and communicates results back through exit codes and stdout.
• Prompt hooks (type: "prompt"): send a prompt to a Claude model for single-turn evaluation. The model returns a yes/no decision as JSON. See Prompt-based hooks.
• Agent hooks (type: "agent"): spawn a subagent that can use tools like Read, Grep, and Glob to verify conditions before returning a decision. See Agent-based hooks.

Common fields

These fields apply to all hook types:

Field	Required	Description
type	yes	"command", "prompt", or "agent"
timeout	no	Seconds before canceling. Defaults: 600 for command, 30 for prompt, 60 for agent
statusMessage	no	Custom spinner message displayed while the hook runs
once	no	If true, runs only once per session then is removed. Skills only, not agents. See Hooks in skills and agents

Command hook fields

In addition to the common fields, command hooks accept these fields:

Field	Required	Description
command	yes	Shell command to execute
async	no	If true, runs in the background without blocking. See Run hooks in the background

Prompt and agent hook fields

In addition to the common fields, prompt and agent hooks accept these fields:

Field	Required	Description
prompt	yes	Prompt text to send to the model. Use $ARGUMENTS as a placeholder for the hook input JSON
model	no	Model to use for evaluation. Defaults to a fast model

All matching hooks run in parallel, and identical handlers are deduplicated automatically. Handlers run in the current directory with Claude Code's environment. The $CLAUDE_CODE_REMOTE environment variable is set to "true" in remote web environments and not set in the local CLI.

Reference scripts by path

Use environment variables to reference hook scripts relative to the project or plugin root, regardless of the working directory when the hook runs:

• $CLAUDE_PROJECT_DIR: the project root. Wrap in quotes to handle paths with spaces.
• ${CLAUDE_PLUGIN_ROOT}: the plugin's root directory, for scripts bundled with a plugin.

This example uses `$CLAUDE_PROJECT_DIR` to run a style checker from the project's `.claude/hooks/` directory after any `Write` or `Edit` tool call:

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

Define plugin hooks in `hooks/hooks.json` with an optional top-level `description` field. When a plugin is enabled, its hooks merge with your user and project hooks.

This example runs a formatting script bundled with the plugin:

```json  theme={null}
{
  "description": "Automatic code formatting",
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Write|Edit",
        "hooks": [
          {
            "type": "command",
            "command": "${CLAUDE_PLUGIN_ROOT}/scripts/format.sh",
            "timeout": 30
          }
        ]
      }
    ]
  }
}
```

See the [plugin components reference](/en/plugins-reference#hooks) for details on creating plugin hooks.

Hooks in skills and agents

In addition to settings files and plugins, hooks can be defined directly in skills and subagents using frontmatter. These hooks are scoped to the component's lifecycle and only run when that component is active.

All hook events are supported. For subagents, Stop hooks are automatically converted to SubagentStop since that is the event that fires when a subagent completes.

Hooks use the same configuration format as settings-based hooks but are scoped to the component's lifetime and cleaned up when it finishes.

This skill defines a PreToolUse hook that runs a security validation script before each Bash command:

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

Agents use the same format in their YAML frontmatter.

The /hooks menu

Type /hooks in Claude Code to open the interactive hooks manager, where you can view, add, and delete hooks without editing settings files directly. For a step-by-step walkthrough, see Set up your first hook in the guide.

Each hook in the menu is labeled with a bracket prefix indicating its source:

• [User]: from ~/.claude/settings.json
• [Project]: from .claude/settings.json
• [Local]: from .claude/settings.local.json
• [Plugin]: from a plugin's hooks/hooks.json, read-only

Disable or remove hooks

To remove a hook, delete its entry from the settings JSON file, or use the /hooks menu and select the hook to delete it.

To temporarily disable all hooks without removing them, set "disableAllHooks": true in your settings file or use the toggle in the /hooks menu. There is no way to disable an individual hook while keeping it in the configuration.

Direct edits to hooks in settings files don't take effect immediately. Claude Code captures a snapshot of hooks at startup and uses it throughout the session. This prevents malicious or accidental hook modifications from taking effect mid-session without your review. If hooks are modified externally, Claude Code warns you and requires review in the /hooks menu before changes apply.

Hook input and output

Hooks receive JSON data via stdin and communicate results through exit codes, stdout, and stderr. This section covers fields and behavior common to all events. Each event's section under Hook events includes its specific input schema and decision control options.

Common input fields

All hook events receive these fields via stdin as JSON, in addition to event-specific fields documented in each hook event section:

Field	Description
session_id	Current session identifier
transcript_path	Path to conversation JSON
cwd	Current working directory when the hook is invoked
permission_mode	Current permission mode: "default", "plan", "acceptEdits", "dontAsk", or "bypassPermissions"
hook_event_name	Name of the event that fired

For example, a PreToolUse hook for a Bash command receives this on stdin:

{
  "session_id": "abc123",
  "transcript_path": "/home/user/.claude/projects/.../transcript.jsonl",
  "cwd": "/home/user/my-project",
  "permission_mode": "default",
  "hook_event_name": "PreToolUse",
  "tool_name": "Bash",
  "tool_input": {
    "command": "npm test"
  }
}

The tool_name and tool_input fields are event-specific. Each hook event section documents the additional fields for that event.

Exit code output

The exit code from your hook command tells Claude Code whether the action should proceed, be blocked, or be ignored.

Exit 0 means success. Claude Code parses stdout for JSON output fields. JSON output is only processed on exit 0. For most events, stdout is only shown in verbose mode (Ctrl+O). The exceptions are UserPromptSubmit and SessionStart, where stdout is added as context that Claude can see and act on.

Exit 2 means a blocking error. Claude Code ignores stdout and any JSON in it. Instead, stderr text is fed back to Claude as an error message. The effect depends on the event: PreToolUse blocks the tool call, UserPromptSubmit rejects the prompt, and so on. See exit code 2 behavior for the full list.

Any other exit code is a non-blocking error. stderr is shown in verbose mode (Ctrl+O) and execution continues.

For example, a hook command script that blocks dangerous Bash commands:

#!/bin/bash
# Reads JSON input from stdin, checks the command
command=$(jq -r '.tool_input.command' < /dev/stdin)

if [[ "$command" == rm* ]]; then
  echo "Blocked: rm commands are not allowed" >&2
  exit 2  # Blocking error: tool call is prevented
fi

exit 0  # Success: tool call proceeds

Exit code 2 behavior per event

Exit code 2 is the way a hook signals "stop, don't do this." The effect depends on the event, because some events represent actions that can be blocked (like a tool call that hasn't happened yet) and others represent things that already happened or can't be prevented.

Hook event	Can block?	What happens on exit 2
PreToolUse	Yes	Blocks the tool call
PermissionRequest	Yes	Denies the permission
UserPromptSubmit	Yes	Blocks prompt processing and erases the prompt
Stop	Yes	Prevents Claude from stopping, continues the conversation
SubagentStop	Yes	Prevents the subagent from stopping
PostToolUse	No	Shows stderr to Claude (tool already ran)
PostToolUseFailure	No	Shows stderr to Claude (tool already failed)
Notification	No	Shows stderr to user only
SubagentStart	No	Shows stderr to user only
SessionStart	No	Shows stderr to user only
SessionEnd	No	Shows stderr to user only
PreCompact	No	Shows stderr to user only

JSON output

Exit codes let you allow or block, but JSON output gives you finer-grained control. Instead of exiting with code 2 to block, exit 0 and print a JSON object to stdout. Claude Code reads specific fields from that JSON to control behavior, including decision control for blocking, allowing, or escalating to the user.

You must choose one approach per hook, not both: either use exit codes alone for signaling, or exit 0 and print JSON for structured control. Claude Code only processes JSON on exit 0. If you exit 2, any JSON is ignored.

Your hook's stdout must contain only the JSON object. If your shell profile prints text on startup, it can interfere with JSON parsing. See JSON validation failed in the troubleshooting guide.

The JSON object supports three kinds of fields:

• Universal fields like continue work across all events. These are listed in the table below.
• Top-level decision and reason are used by some events to block or provide feedback.
• hookSpecificOutput is a nested object for events that need richer control. It requires a hookEventName field set to the event name.

Field	Default	Description
continue	true	If false, Claude stops processing entirely after the hook runs. Takes precedence over any event-specific decision fields
stopReason	none	Message shown to the user when continue is false. Not shown to Claude
suppressOutput	false	If true, hides stdout from verbose mode output
systemMessage	none	Warning message shown to the user

To stop Claude entirely regardless of event type:

{ "continue": false, "stopReason": "Build failed, fix errors before continuing" }

Decision control

Not every event supports blocking or controlling behavior through JSON. The events that do each use a different set of fields to express that decision. Use this table as a quick reference before writing a hook:

Events	Decision pattern	Key fields
UserPromptSubmit, PostToolUse, PostToolUseFailure, Stop, SubagentStop	Top-level decision	decision: "block", reason
PreToolUse	hookSpecificOutput	permissionDecision (allow/deny/ask), permissionDecisionReason
PermissionRequest	hookSpecificOutput	decision.behavior (allow/deny)

Here are examples of each pattern in action:

Used by `UserPromptSubmit`, `PostToolUse`, `PostToolUseFailure`, `Stop`, and `SubagentStop`. The only value is `"block"` — to allow the action to proceed, omit `decision` from your JSON, or exit 0 without any JSON at all:

```json  theme={null}
{
  "decision": "block",
  "reason": "Test suite must pass before proceeding"
}
```

Uses `hookSpecificOutput` for richer control: allow, deny, or escalate to the user. You can also modify tool input before it runs or inject additional context for Claude. See [PreToolUse decision control](#pretooluse-decision-control) for the full set of options.

```json  theme={null}
{
  "hookSpecificOutput": {
    "hookEventName": "PreToolUse",
    "permissionDecision": "deny",
    "permissionDecisionReason": "Database writes are not allowed"
  }
}
```

Uses `hookSpecificOutput` to allow or deny a permission request on behalf of the user. When allowing, you can also modify the tool's input or apply permission rules so the user isn't prompted again. See [PermissionRequest decision control](#permissionrequest-decision-control) for the full set of options.

```json  theme={null}
{
  "hookSpecificOutput": {
    "hookEventName": "PermissionRequest",
    "decision": {
      "behavior": "allow",
      "updatedInput": {
        "command": "npm run lint"
      }
    }
  }
}
```

For extended examples including Bash command validation, prompt filtering, and auto-approval scripts, see What you can automate in the guide and the Bash command validator reference implementation.

Hook events

Each event corresponds to a point in Claude Code's lifecycle where hooks can run. The sections below are ordered to match the lifecycle: from session setup through the agentic loop to session end. Each section describes when the event fires, what matchers it supports, the JSON input it receives, and how to control behavior through output.

SessionStart

Runs when Claude Code starts a new session or resumes an existing session. Useful for loading development context like existing issues or recent changes to your codebase, or setting up environment variables. For static context that does not require a script, use CLAUDE.md instead.

SessionStart runs on every session, so keep these hooks fast.

The matcher value corresponds to how the session was initiated:

Matcher	When it fires
startup	New session
resume	--resume, --continue, or /resume
clear	/clear
compact	Auto or manual compaction

SessionStart input

In addition to the common input fields, SessionStart hooks receive source, model, and optionally agent_type. The source field indicates how the session started: "startup" for new sessions, "resume" for resumed sessions, "clear" after /clear, or "compact" after compaction. The model field contains the model identifier. If you start Claude Code with claude --agent <name>, an agent_type field contains the agent name.

{
  "session_id": "abc123",
  "transcript_path": "/Users/.../.claude/projects/.../00893aaf-19fa-41d2-8238-13269b9b3ca0.jsonl",
  "cwd": "/Users/...",
  "permission_mode": "default",
  "hook_event_name": "SessionStart",
  "source": "startup",
  "model": "claude-sonnet-4-5-20250929"
}

SessionStart decision control

Any text your hook script prints to stdout is added as context for Claude. In addition to the JSON output fields available to all hooks, you can return these event-specific fields:

Field	Description
additionalContext	String added to Claude's context. Multiple hooks' values are concatenated

{
  "hookSpecificOutput": {
    "hookEventName": "SessionStart",
    "additionalContext": "My additional context here"
  }
}

Persist environment variables

SessionStart hooks have access to the CLAUDE_ENV_FILE environment variable, which provides a file path where you can persist environment variables for subsequent Bash commands.

To set individual environment variables, write export statements to CLAUDE_ENV_FILE. Use append (>>) to preserve variables set by other hooks:

#!/bin/bash

if [ -n "$CLAUDE_ENV_FILE" ]; then
  echo 'export NODE_ENV=production' >> "$CLAUDE_ENV_FILE"
  echo 'export DEBUG_LOG=true' >> "$CLAUDE_ENV_FILE"
  echo 'export PATH="$PATH:./node_modules/.bin"' >> "$CLAUDE_ENV_FILE"
fi

exit 0

To capture all environment changes from setup commands, compare the exported variables before and after:

#!/bin/bash

ENV_BEFORE=$(export -p | sort)

# Run your setup commands that modify the 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

Any variables written to this file will be available in all subsequent Bash commands that Claude Code executes during the session.

`CLAUDE_ENV_FILE` is available for SessionStart hooks. Other hook types do not have access to this variable.

UserPromptSubmit

Runs when the user submits a prompt, before Claude processes it. This allows you to add additional context based on the prompt/conversation, validate prompts, or block certain types of prompts.

UserPromptSubmit input

In addition to the common input fields, UserPromptSubmit hooks receive the prompt field containing the text the user submitted.

{
  "session_id": "abc123",
  "transcript_path": "/Users/.../.claude/projects/.../00893aaf-19fa-41d2-8238-13269b9b3ca0.jsonl",
  "cwd": "/Users/...",
  "permission_mode": "default",
  "hook_event_name": "UserPromptSubmit",
  "prompt": "Write a function to calculate the factorial of a number"
}

UserPromptSubmit decision control

UserPromptSubmit hooks can control whether a user prompt is processed and add context. All JSON output fields are available.

There are two ways to add context to the conversation on exit code 0:

• Plain text stdout: any non-JSON text written to stdout is added as context
• JSON with additionalContext: use the JSON format below for more control. The additionalContext field is added as context

Plain stdout is shown as hook output in the transcript. The additionalContext field is added more discretely.

To block a prompt, return a JSON object with decision set to "block":

Field	Description
decision	"block" prevents the prompt from being processed and erases it from context. Omit to allow the prompt to proceed
reason	Shown to the user when decision is "block". Not added to context
additionalContext	String added to Claude's context

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

The JSON format isn't required for simple use cases. To add context, you can print plain text to stdout with exit code 0. Use JSON when you need to block prompts or want more structured control.

PreToolUse

Runs after Claude creates tool parameters and before processing the tool call. Matches on tool name: Bash, Edit, Write, Read, Glob, Grep, Task, WebFetch, WebSearch, and any MCP tool names.

Use PreToolUse decision control to allow, deny, or ask for permission to use the tool.

PreToolUse input

In addition to the common input fields, PreToolUse hooks receive tool_name, tool_input, and tool_use_id. The tool_input fields depend on the tool:

Bash

Executes shell commands.

Field	Type	Example	Description
command	string	"npm test"	The shell command to execute
description	string	"Run test suite"	Optional description of what the command does
timeout	number	120000	Optional timeout in milliseconds
run_in_background	boolean	false	Whether to run the command in background

Write

Creates or overwrites a file.

Field	Type	Example	Description
file_path	string	"/path/to/file.txt"	Absolute path to the file to write
content	string	"file content"	Content to write to the file

Edit

Replaces a string in an existing file.

Field	Type	Example	Description
file_path	string	"/path/to/file.txt"	Absolute path to the file to edit
old_string	string	"original text"	Text to find and replace
new_string	string	"replacement text"	Replacement text
replace_all	boolean	false	Whether to replace all occurrences

Read

Reads file contents.

Field	Type	Example	Description
file_path	string	"/path/to/file.txt"	Absolute path to the file to read
offset	number	10	Optional line number to start reading from
limit	number	50	Optional number of lines to read

Glob

Finds files matching a glob pattern.

Field	Type	Example	Description
pattern	string	"**/*.ts"	Glob pattern to match files against
path	string	"/path/to/dir"	Optional directory to search in. Defaults to current working directory

Grep

Searches file contents with regular expressions.

Field	Type	Example	Description
pattern	string	"TODO.*fix"	Regular expression pattern to search for
path	string	"/path/to/dir"	Optional file or directory to search in
glob	string	"*.ts"	Optional glob pattern to filter files
output_mode	string	"content"	"content", "files_with_matches", or "count". Defaults to "files_with_matches"
-i	boolean	true	Case insensitive search