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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.

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 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

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:

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

<Note>
  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/).
</Note>

### 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.

<Steps>
  <Step title="Create the hook script">
    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
    ```
  </Step>

  <Step title="Make the script executable (macOS/Linux)">
    Hook scripts must be executable for Claude Code to run them:

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

  <Step title="Register the hook">
    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"
              }
            ]
          }
        ]
      }
    }
    ```
  </Step>
</Steps>

### 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:

```json  theme={null}
{
  "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
TeammateIdle When an agent team teammate is about to go idle
TaskCompleted When a task is being marked as completed
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:

```json theme={null} { "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](/en/hooks#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:

```bash  theme={null}
#!/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:

```json theme={null} { "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](/en/hooks#decision-control) 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](#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:

```json  theme={null}
{
  "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, 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
UserPromptSubmit, Stop, TeammateIdle, TaskCompleted 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__<server>__<tool>, where <server> is the MCP server name and <tool> 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 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:

```json theme={null} { "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](/en/hooks#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:

```json  theme={null}
{
  "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: bash theme={null} 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:

```bash theme={null}

!/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:

```bash  theme={null}
# 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.

Adapter flow for little-loops hooks

little-loops ships a host-agnostic hook layer so you can author a hook once in Python and run it from Claude Code, OpenCode, Codex CLI, or any other agent host that has an adapter. The host event flows through a thin adapter (a bash shim for Claude Code and Codex CLI, a TypeScript plugin for OpenCode) into the Python dispatcher, the dispatcher routes to a handler, and the handler's LLHookResult flows back out:

flowchart LR
    HOST[Host event<br/>Claude Code, OpenCode, or Codex] --> ADAPTER[Adapter<br/>bash shim or TS plugin]
    ADAPTER --> SUBPROC[python -m little_loops.hooks &lt;intent&gt;]
    SUBPROC --> MAIN[main_hooks dispatch]
    MAIN --> HANDLER[handle&#40;event&#41;]
    HANDLER --> RESULT[LLHookResult]
    RESULT --> ADAPTERBACK[Adapter]
    ADAPTERBACK --> HOSTBACK[Host response]

See Write a little-loops hook for the full authoring walkthrough: handler signature, registration via the LLHookIntentExtension Protocol, and the pure-function + subprocess testing patterns.

Learn more