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By default, the agent has access to bash, file read/write, and Python — the same tools available in Claude Code. You can restrict these and add custom tools via MCP servers.

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Default Tools

The agent runs with all Claude Code tools enabled. To restrict which tools the agent can use, pass allowedTools: 
const session = await sandbox.agent.start({
  prompt: "Analyze the CSV files in /data",
  allowedTools: ["Read", "Bash"],
});

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MCP Servers

Model Context Protocol servers give the agent access to custom tools. MCP servers run inside the sandbox — the agent discovers available tools via the protocol. Pass MCP server configuration when starting the agent: 
const session = await sandbox.agent.start({
  prompt: "Query the users table and summarize the results",
  mcpServers: {
    sqlite: {
      command: "npx",
      args: ["-y", "@modelcontextprotocol/server-sqlite", "/data/app.db"],
    },
  },
});

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McpServerConfig

FieldTypeRequiredDescription
commandstringYesCommand to start the MCP server
argsstring[]NoCommand arguments
envobjectNoEnvironment variables for the server process

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Example: Custom API Tool

const session = await sandbox.agent.start({
  prompt: "Fetch the latest deployment status",
  mcpServers: {
    deploy: {
      command: "node",
      args: ["/tools/deploy-server.js"],
      env: { DEPLOY_API_KEY: process.env.DEPLOY_API_KEY },
    },
  },
});

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System Prompt

Steer agent behavior with a custom system prompt: 
const session = await sandbox.agent.start({
  prompt: "Review the codebase for security issues",
  systemPrompt: "You are a security auditor. Focus on OWASP Top 10 vulnerabilities. Output findings as a markdown checklist.",
});

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Permission Mode

Controls how the agent handles tool permissions: 
const session = await sandbox.agent.start({
  prompt: "Set up the project",
  permissionMode: "bypassPermissions", // default — agent runs freely
});
The default is bypassPermissions — the agent can use any available tool without confirmation. This is safe because the agent runs inside an isolated sandbox VM.

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Max Turns

Limit how many think → act → observe iterations the agent can perform: 
const session = await sandbox.agent.start({
  prompt: "Fix the failing test",
  maxTurns: 10, // default: 50
});
Lower maxTurns to prevent runaway agents on simple tasks. The default is 50.
Back to Agents overview. See also: Events · Multi-turn.