What is npx?

npx is a command-line tool that ships with Node.js and npm for running an npm package without installing it globally first. You give it a package name and it resolves the package, fetches it into a cache if it is not already present, and runs its executable, all in a single command. In the MCP ecosystem this makes npx the default way to launch local, stdio-based servers written in JavaScript or TypeScript: a client's config typically lists a command of npx with args like ["-y", "@modelcontextprotocol/server-filesystem", "/path"]. The -y (or --yes) flag auto-confirms the install prompt so the server starts unattended, and pinning a version (package@1.2.3) keeps the launch reproducible instead of silently pulling the latest release. Because npx grabs the current published version on first run, it is convenient for trying servers quickly but means you are executing third-party code from the registry, so it is worth pinning versions and trusting the publisher. The Python ecosystem's equivalent is uvx, which plays the same role for uv/pip-distributed servers.