Core System

Tool System

45 tools, 3 execution modes — AI's Swiss Army knife

~7 min read

Built-in tools

What Is This? #

Imagine Claude is a handyman and the tool system is its toolbox.

When you say 'help me fix this bug', Claude opens the toolbox: uses search tools to find relevant code, file read tools to view content, edit tools to modify code, and Bash to run tests. It picks the right tools in the right order.

Even smarter: it can search multiple files simultaneously (parallel), but must modify files one at a time (serial) to avoid messing things up.

Tool Catalog #

Hover to see what each tool does

Shell Execution

Bash

PowerShell

REPL

File Operations

Read

Write

Edit

NotebookEdit

EnterWorktree

ExitWorktree

Search & Discovery

Glob

Grep

ToolSearch

Web Access

WebFetch

WebSearch

Agent & Coordination

Agent

SendMessage

TeamCreate

TeamDelete

Skill

RemoteTrigger

Task Management

TaskCreate

TaskUpdate

TaskList

TaskGet

TaskOutput

TaskStop

TodoWrite

MCP Protocol

MCPTool

ListMcpResources

ReadMcpResource

McpAuth

Configuration & IDE

Config

AskUserQuestion

CronCreate

LSP

EnterPlanMode

ExitPlanMode

CronDelete

CronList

Sleep

StructuredOutput

Brief

Execution Flow #

A tool call's complete journey from parsing to result

Parse tool_use

↓

Input Validation

↓

Permission Check

↓allowed

Execute Tool

↓

PostToolUse Hook

↓

Return Result

Scheduling Strategy #

Read parallel, write serial — click Run to see it in action

Tool Scheduling Simulator

Phase 1 — Read Operations (Parallel)

Glob('*.ts')

Grep('TODO')

Read('main.tsx')

Phase 2 — Write Operations (Serial)

Edit('main.tsx')

Write('test.ts')

Bash('npm test')

Core Code #

Simplified tool scheduling implementation

src/tools.tsTool Registration

Step 1 of 5

1// src/tools.ts — Tool registration with feature gates

2export function getAllBaseTools(): Tool[] {

3 return [

4 // File system tools (always enabled)

5 new ReadTool(),

6 new WriteTool(),

7 new EditTool(),

8 new GlobTool(),

9 new GrepTool(),

11 // Bash execution

12 new BashTool(),

14 // Feature-gated tools

15 ...(feature("notebooks") ? [new NotebookEditTool()] : []),

16 ...(feature("mcp") ? [new McpTool()] : []),

18 // Internal-only tools (runtime check)

19 ...(process.env.USER_TYPE === "internal"

20 ? [new DebugTool(), new ProfileTool()]

21 : []),

22 ];

23}

All tools are registered in a single array. Feature flags like feature('X') are evaluated at bundle time — disabled tools are stripped from production. Runtime checks (process.env) gate internal-only tools.

Query Pipeline

The complete journey from pressing Enter to Claude's response

Permissions

Three-layer defense-in-depth — powerful yet safe AI

Agents

Multi-agent coordination for complex tasks