This MCP server implements the Model Context Protocol (MCP) to execute arbitrary JavaScript inside isolated, ephemeral Docker containers, with on-the-fly npm dependency installation. It supports starting and managing Node.js sandbox containers, executing shell commands inside them, and installing per-job npm dependencies before running code. JavaScript snippets can be written as ES modules and their standard output is captured for the response. After execution, containers are torn down cleanly unless detached mode is used to keep them alive for long-running services. The server emphasizes reproducibility and isolation, and offers guidance for ephemeral usage (no persistent host storage). It is intended to be used via MCP clients (e.g., Claude Desktop, VS Code) and can be run locally with Docker or via NPX. The README also outlines example prompts to validate functionality (e.g., printing Hello World, generating files like qrcode.png), and provides configurations for Docker and NPX usage, as well as a VS Code setup. Tools exposed include run_js_ephemeral, sandbox_initialize, sandbox_exec, run_js, sandbox_stop, and search_npm_packages, enabling a full lifecycle of sandbox management, code execution, and package discovery.