Tools
Claude Code provides 40+ built-in tools plus dynamically loaded MCP tools. Tools are invoked by the AI model via tool_use blocks and executed through the StreamingToolExecutor with permission gating.
How Tools Work
Tools are defined with Zod schemas in src/Tool.ts via the buildTool() helper and registered in src/tools.ts. Each tool declares its input schema, output schema, concurrency safety, read-only status, and permission requirements.
Model emits tool_use
→ Tool call normalization (toolCallParser.ts)
→ Permission check (permissions.ts)
→ PreToolUse hooks (plugins)
→ Tool execution (StreamingToolExecutor)
→ PostToolUse hooks (plugins)
→ Result returned as tool_result
→ Query loop continues
File & Code Operations
| Tool | Description | Schemas |
|---|
Read (FileReadTool) | Read files with line numbers, supports images, PDFs, Jupyter notebooks | Zod |
Write (FileWriteTool) | Create new files with full content | Zod |
Edit (FileEditTool) | Exact string replacement edits (surgical, diff-based) | Zod |
Glob (GlobTool) | Fast file pattern matching, sorted by modification time | Zod |
Grep (GrepTool) | Regex content search with context lines and multiline support | Zod |
NotebookEdit (NotebookEditTool) | Edit Jupyter notebook cells (replace, insert, delete) | Zod |
JsonPath (JsonPathTool) | Query, validate, format, and transform JSON data | Zod |
Shell & System
| Tool | Description |
|---|
Bash (BashTool) | Execute shell commands with timeout, background, sandbox support, and permission gating |
PowerShell (PowerShellTool) | PowerShell execution on Windows (feature-gated) |
Monitor (MonitorTool) | Stream stdout/stderr from background tasks in real-time |
TaskOutput (TaskOutputTool) | Get output from running or completed tasks |
TaskStop (TaskStopTool) | Stop running background tasks |
Search & Web
| Tool | Description |
|---|
WebSearch (WebSearchTool) | Multi-provider web search (Tavily, Brave, Serper, SearXNG, DuckDuckGo) |
WebFetch (WebFetchTool) | Fetch and analyze content from specific URLs |
SessionSearch (SessionSearchTool) | Full-text search across past session transcripts |
CodeIndex (CodeIndexTool) | Fuzzy code search across indexed codebase (feature-gated: CODE_INDEX) |
ToolSearch (ToolSearchTool) | Keyword search for deferred/lazy-loaded tools |
Browser & Automation
| Tool | Description |
|---|
Browser (BrowserTool) | Stealth Playwright browser — navigate, click, type, screenshot, extract, fill forms |
ComputerUse (ComputerUseTool) | Windows-only computer use automation (feature-gated: ENABLE_COMPUTER_USE) |
Agent & Task Management
| Tool | Description |
|---|
Skill (SkillTool) | Invoke skills and prompt-type commands by name |
AskUserQuestion (AskUserQuestionTool) | Ask the user interactive questions during execution |
SendMessage (SendMessageTool) | Send messages between agents in coordinator mode |
EnterPlanMode (EnterPlanModeTool) | Enter structured plan mode for complex tasks |
ExitPlanMode (ExitPlanModeV2Tool) | Exit plan mode and proceed with implementation |
EnterWorktree / ExitWorktree | Create/exit isolated git worktrees (feature-gated) |
TaskCreate / TaskGet / TaskUpdate / TaskList | Structured task tracking (V2 todo system) |
TodoWrite (TodoWriteTool) | Write todo items for task tracking |
Config (ConfigTool) | Configuration management (ant-only) |
Brief (BriefTool) | Generate brief summaries |
Scheduled Tasks
Scheduled tasks can be created from the interactive /task form. The form collects a name, project, schedule type, prompt, and storage mode, then creates the matching cron task through the same scheduling runtime used by CronCreate, CronList, and CronDelete.
| User action | Behavior |
|---|
/task | Open the interactive scheduled task form |
Select Daily around 09:00 | Create a recurring daily task |
Select Weekdays around 09:00 | Create a weekday cron such as 0 9 * * 1-5 |
Select In N minutes with 10 | Create a one-shot reminder |
Select Custom cron | Use a standard 5-field cron expression |
/task scheduled | Open the same form explicitly |
- Durable storage persists tasks to
.claude/scheduled_tasks.json across sessions.
- Session-only storage keeps tasks in memory for the current session only.
- Recurring tasks auto-expire after 30 days unless they are system-created permanent tasks.
- One-shot tasks auto-delete after firing.
- Natural language scheduling can still use the model-facing cron tools directly.
/task
Name: Server status
Schedule: Daily
Time: 20:00
Prompt: Check the server status
Storage: Durable
MCP (Model Context Protocol)
| Tool | Description |
|---|
ListMcpResources (ListMcpResourcesTool) | List available resources from connected MCP servers |
ReadMcpResource (ReadMcpResourceTool) | Read resources exposed by MCP servers |
| MCP-provided tools | Dynamically loaded tools from MCP servers (filesystem, database, APIs) |
Feature-Gated Tools
| Tool | Flag | Description |
|---|
LSP (LSPTool) | ENABLE_LSP_TOOL=1 | Language Server Protocol integration |
ComputerUse | ENABLE_COMPUTER_USE=1 (Win) | Windows GUI automation |
CodeIndex | CODE_INDEX feature | Fuzzy code search |
EnterWorktree / ExitWorktree | Worktree mode | Git worktree isolation |
TeamCreate / TeamDelete / RequestShutdown | Agent swarms | Multi-agent team management |
SubscribePrActivity / UnsubscribePrActivity | Agent swarms | PR activity monitoring |
CronCreate / CronDelete / CronList | AGENT_TRIGGERS | Scheduled task triggers |
PushNotification | KAIROS | Push notification support |
Tool Safety & Permissions
Each tool declares:
- isEnabled() — Whether the tool is available in the current build
- isConcurrencySafe() — Can run in parallel with other tools
- isReadOnly() — Does not modify filesystem
- isDestructive() — Performs irreversible operations
- checkPermissions() — Tool-specific permission logic
- validateInput() — Input validation before execution
- maxResultSizeChars — Max result size before disk persistence
MCP tools from external servers are merged into the tool pool at runtime via assembleToolPool(). Tools are filtered by deny rules from the permission context.
CLAUDE_CODE_SIMPLE mode
Setting CLAUDE_CODE_SIMPLE=1 or using --bare limits tools to a minimal set: Bash, Read, Edit.