> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/instructkr/claude-code/llms.txt
> Use this file to discover all available pages before exploring further.

# Tools overview

> Tools are the capabilities Claude can invoke during a session — reading files, running commands, searching the codebase, fetching URLs, and more.

Tools are discrete, self-contained capabilities that Claude invokes during a session to accomplish tasks. Each tool has a defined input schema, a permission level, and an execution function. Claude selects the appropriate tool based on what the task requires, then waits for the result before continuing.

## How the tool loop works

<Steps>
  <Step title="Claude selects a tool">
    After analyzing the conversation, Claude emits a `tool_use` block specifying the tool name and its input arguments.
  </Step>

  <Step title="Permission check">
    The permission system evaluates whether the tool call is allowed under the current permission mode (`default`, `plan`, `bypassPermissions`, etc.). Depending on the outcome, the tool call is automatically approved, denied, or presented to you for a yes/no decision.
  </Step>

  <Step title="Tool executes">
    The tool runs — reading a file, executing a shell command, fetching a URL, spawning a sub-agent, and so on. Progress is streamed to the terminal UI in real time.
  </Step>

  <Step title="Result returned">
    The tool returns a result, which is injected into the conversation context as a `tool_result` block. Claude then continues from where it left off, using the new information.
  </Step>
</Steps>

## Permission levels

Each tool has a permission level that determines when you need to approve its use.

| Level                         | Description                                                                                                                     | Examples                                                   |
| ----------------------------- | ------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------- |
| **Read-only**                 | Does not modify any files or system state. Automatically approved in most modes.                                                | `FileReadTool`, `GlobTool`, `GrepTool`, `WebFetchTool`     |
| **Mutating**                  | Creates or modifies files or state. Requires approval unless the path is in an allowlist or `bypassPermissions` mode is active. | `FileWriteTool`, `FileEditTool`, `NotebookEditTool`        |
| **Destructive / side-effect** | Executes shell commands, spawns agents, or has network side-effects. Requires explicit approval unless pre-approved.            | `BashTool`, `AgentTool`, `TeamCreateTool`, `WebSearchTool` |

<Info>
  The permission model is documented in detail in [Permission model](/concepts/permission-model). You can pre-approve specific paths or commands in your local settings to avoid repeated prompts.
</Info>

## Controlling available tools

You can restrict which tools Claude can use in a session using CLI flags.

**Allow only specific tools:**

```bash theme={null}
claude --allowedTools FileReadTool,GlobTool,GrepTool
```

**Block specific tools:**

```bash theme={null}
claude --disallowedTools BashTool,WebFetchTool
```

Both flags accept a comma-separated list of tool names. `--allowedTools` takes precedence — only the listed tools will be available. `--disallowedTools` removes specific tools from the default set.

<Tip>
  Use `--allowedTools` for read-only sessions where you want Claude to explore the codebase without making changes.
</Tip>

## Complete tool reference

The table below lists every built-in tool. Tools marked with a feature flag may not be available in all configurations.

| Tool                  | Category | Description                                        | Permission level |
| --------------------- | -------- | -------------------------------------------------- | ---------------- |
| `BashTool`            | Shell    | Execute shell commands in a persistent session     | Destructive      |
| `FileReadTool`        | File     | Read files — text, images, PDFs, Jupyter notebooks | Read-only        |
| `FileWriteTool`       | File     | Create or overwrite a file with new content        | Mutating         |
| `FileEditTool`        | File     | Partial file edit via exact string replacement     | Mutating         |
| `GlobTool`            | Search   | Find files by glob pattern                         | Read-only        |
| `GrepTool`            | Search   | Search file contents with regex (ripgrep)          | Read-only        |
| `WebFetchTool`        | Web      | Fetch and extract content from a URL               | Read-only        |
| `WebSearchTool`       | Web      | Search the web for current information             | Read-only        |
| `AgentTool`           | Agent    | Spawn a sub-agent to handle a complex task         | Destructive      |
| `SkillTool`           | Agent    | Execute a named skill (reusable workflow)          | Destructive      |
| `MCPTool`             | Agent    | Invoke a tool from a connected MCP server          | Varies           |
| `LSPTool`             | Agent    | Language Server Protocol diagnostics and hover     | Read-only        |
| `NotebookEditTool`    | File     | Edit cells in a Jupyter notebook                   | Mutating         |
| `TaskCreateTool`      | Task     | Create a task in the shared task list              | Mutating         |
| `TaskUpdateTool`      | Task     | Update task status, owner, or metadata             | Mutating         |
| `TaskGetTool`         | Task     | Retrieve a single task by ID                       | Read-only        |
| `TaskListTool`        | Task     | List all tasks in the current task list            | Read-only        |
| `TaskStopTool`        | Task     | Stop a running task                                | Mutating         |
| `TaskOutputTool`      | Task     | Read the output file of a completed agent task     | Read-only        |
| `SendMessageTool`     | Agent    | Send a message to another agent in a swarm         | Mutating         |
| `TeamCreateTool`      | Agent    | Create a named team for multi-agent coordination   | Mutating         |
| `TeamDeleteTool`      | Agent    | Delete a team and clean up its resources           | Mutating         |
| `EnterPlanModeTool`   | Session  | Switch to plan mode (propose without executing)    | Mutating         |
| `ExitPlanModeTool`    | Session  | Exit plan mode and resume normal execution         | Mutating         |
| `EnterWorktreeTool`   | Session  | Isolate work in a temporary git worktree           | Mutating         |
| `ExitWorktreeTool`    | Session  | Exit the current git worktree                      | Mutating         |
| `RemoteTriggerTool`   | Session  | Register a remote trigger for proactive mode       | Mutating         |
| `ScheduleCronTool`    | Session  | Schedule a cron-style recurring trigger            | Mutating         |
| `SleepTool`           | Session  | Pause execution in proactive/KAIROS mode           | Read-only        |
| `SyntheticOutputTool` | Session  | Emit structured output from the agent              | Mutating         |
| `ToolSearchTool`      | Agent    | Discover tools by name or description              | Read-only        |
| `AskUserQuestionTool` | Session  | Ask you a clarifying question mid-task             | Read-only        |
| `REPLTool`            | Shell    | Interactive REPL for code evaluation (internal)    | Destructive      |
| `PowerShellTool`      | Shell    | Execute PowerShell commands on Windows             | Destructive      |

## Tool categories

<CardGroup cols={2}>
  <Card title="File tools" icon="file" href="/reference/tools/file-tools">
    Read, write, and edit files. Covers `FileReadTool`, `FileWriteTool`, `FileEditTool`, and `NotebookEditTool`.
  </Card>

  <Card title="Search tools" icon="magnifying-glass" href="/reference/tools/search-tools">
    Find files and search content. Covers `GlobTool`, `GrepTool`, and search patterns with `BashTool`.
  </Card>

  <Card title="Agent tools" icon="robot" href="/reference/tools/agent-tools">
    Multi-agent workflows, task management, and inter-agent messaging.
  </Card>

  <Card title="Web tools" icon="globe" href="/reference/tools/web-tools">
    Fetch URLs and search the web. Covers `WebFetchTool` and `WebSearchTool`.
  </Card>
</CardGroup>