Give Claude a safe box with a dev container

The steps

One step at a time. When a step’s check matches, tick it and the next one opens.

1. 01

   Step 1 of 3: Add the Claude Code feature

   Create .devcontainer/devcontainer.json with the official Claude Code feature.

   Save this file in your project, by hand or by pasting the prompt into Claude Code. The feature installs Claude Code, and Node.js if the image lacks it. With your own image or Dockerfile, add only the features block.

   Or let Claude create itCopy

   Create .devcontainer/devcontainer.json in this project with exactly this content, and nothing else:
   
   {
     "image": "mcr.microsoft.com/devcontainers/base:ubuntu",
     "features": {
       "ghcr.io/anthropics/devcontainer-features/claude-code:1.0": {}
     }
   }

   Changes to .devcontainer/devcontainer.jsonBefore → after

   +Added: {

   +Added: "image": "mcr.microsoft.com/devcontainers/base:ubuntu",

   +Added: "features": {

   +Added: "ghcr.io/anthropics/devcontainer-features/claude-code:1.0": {}

   +Added: }

   +Added: }

   Check it worked

   The file sits at .devcontainer/devcontainer.json in your project’s top folder.

   It worked — next step Not yet
2. 02

   Step 2 of 3: Open the project in the container

   Rebuild the container in VS Code, then sign in to Claude Code inside it.

   Open the Command Palette (Cmd+Shift+P on Mac, Ctrl+Shift+P on Windows and Linux) and run Dev Containers: Reopen in Container (or Rebuild Container if you’re already in one). When it finishes, open a terminal in VS Code.

   TerminalCopy

   Run: $ claude

   – What happens: Follow the sign-in prompt. If the browser never hands back, paste its code at Paste code here if prompted.

   Check it worked

   Claude Code starts in the VS Code terminal and you are signed in.

   If it didn’t work

   The build stops with Failed to install Node.js and npm

   Add "ghcr.io/devcontainers/features/node:1": {} to the features block, above the Claude Code feature, and rebuild.

   It worked — next step Not yet Back
3. 03

   Step 3 of 3: Know what the box holds back

   Commands stay in the container. Your project files and the network don’t.

   Ask Claude to add a comment to a file. Claude and its commands run inside the container, but the edit lands in your real project folder, because the container mounts it from your machine.

   Kept inside the container

   • Commands Claude runs, and what they install

   Still reachable

   • Every file in your mounted project folder
   • The network, unless you restrict outbound traffic
   • Credentials in the container’s ~/.claude, and anything you mount

   Warning: With --dangerously-skip-permissions, a malicious project can send out anything in the container, your Claude credentials included. Use the container only with repositories you trust.

   Check it worked

   The comment Claude added shows in the file on your machine, outside the container.

   It worked — finish Not yet Back