js-sandbox MCP Server

What is js-sandbox?

A Model Context Protocol server that provides a secure, isolated JavaScript execution environment. It is designed for developers and AI assistants that need to run untrusted JavaScript code safely, with configurable limits on execution time and memory.

How to use js-sandbox?

Install dependencies with npm install, then build the server with npm run build. Configure it in Claude Desktop by adding the path to build/index.js in the claude_desktop_config.json file. Use the execute_js tool to run code, optionally setting a timeout (100–30000ms) and memory limit (1MB–100MB).

Key features of js-sandbox

• Single execute_js tool for running JavaScript code
• Isolated environment with configurable execution time (100–30000ms)
• Configurable memory limits (1MB–100MB)
• Protection against malicious or runaway code
• Easy integration with Claude Desktop via stdio

Use cases of js-sandbox

• Executing user-provided JavaScript safely within an AI assistant conversation
• Testing short JavaScript snippets in a controlled sandbox
• Allowing AI tools to run dynamic code without risking the host system

FAQ from js-sandbox

What command-line invocation does js-sandbox use?

It is launched as a stdio server by pointing Claude Desktop (or any MCP host) to the built index.js file.

What tools does js-sandbox provide?

It exposes one tool: execute_js, which accepts the required parameter code, and optional parameters timeout and memory.

How do I debug js-sandbox?

Since MCP servers communicate over stdio, debugging is best done using the MCP Inspector, available via npm run inspector, which provides a browser-based debugging URL.

What are the runtime dependencies?

Node.js and npm are required for development and building, as the server is written in JavaScript and runs via node on the host system.

Where is the server configuration stored?

For Claude Desktop, the configuration file is located at ~/Library/Application Support/Claude/claude_desktop_config.json on macOS or %APPDATA%/Claude/claude_desktop_config.json on Windows.