Test a desktop app with your coding agent

For a web page, a browser tool such as Playwright's MCP server is often enough. For an Electron, Tauri, Qt or GTK app, or anything outside a browser, the agent needs a real desktop. Legato runs one in a container on your machine, with your app installed and your project mounted, and gives your coding agent the screen through MCP.

1. An image with your app. Start from Legato's desktop image and add what your app needs:

   FROM ghcr.io/legatolabs/desktop
   USER root
   RUN apt-get update && apt-get install -y --no-install-recommends libgtk-3-0 libnss3 && rm -rf /var/lib/apt/lists/*
   USER user
   

   docker build -t my-app-desktop .

2. The MCP server on that image, with your project mounted.

   claude mcp add legato -e LEGATO_DOCKER_ARGS="-v $PWD:/home/user/project" -- legato mcp --sandbox docker:my-app-desktop
   

3. Ask. "Open a terminal on the Legato desktop, start ~/project/dist/my-app, and check that the settings window saves the theme."

• Saving files. The desktop's user is uid 1000. On Linux, files you mount must be writable by that uid for the app to save them.
• Electron and other Chromium-based apps usually need --no-sandbox inside a container.
• Your dev server is at http://host.docker.internal:PORT from inside the desktop.
• To see what the agent did afterwards, add --record DIR to legato mcp (MCP server).

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