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What is an environment?

An environment defines how the sandbox is set up when you start a session. It tells Magnet which repository to clone, how to install dependencies, and optionally how to run a dev server with a live preview. You can create multiple environments — one per project or repository — and select which to use when starting a session.

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Creating an environment

Go to Settings > Sandbox and click New Environment, or create one during the setup wizard.

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Repository

Choose a GitHub repository and branch. The sandbox will clone this repo when a session starts.
  • GitHub Repository — select from your connected repositories
  • Branch — the branch to clone (defaults to main)

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Environment settings

  • Name — a label for this environment (auto-suggested from the repo name)
  • Enabled — disabled environments can’t be used for sessions
  • Default — the environment pre-selected when starting new sessions

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Setup script

Commands that run after the repo is cloned — typically used to install dependencies. 
pnpm install
You can run multiple commands: 
pnpm install
cp .env.example .env

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Run script

A command to start your development server. This runs in the background while the agent works. 
pnpm dev

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Preview port

The port your dev server listens on. When configured, Magnet provides a preview URL that lets you see your app running live inside the sandbox. For example, if your Next.js app runs on port 5173, set the preview port to 5173. You’ll get a URL you can open in your browser to see the app as the agent makes changes.
Port 3000 is reserved for Magnet’s internal server. Use a different port for your app.

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Node.js version

Choose between Node 20 (LTS Active) and Node 22 (LTS Current).

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Environment variables

Add environment variables and secrets that your project needs. These are injected into the sandbox when the session starts. Common use cases:
  • API keys for third-party services
  • Database connection strings
  • Feature flags
Variables marked as secret are encrypted and never displayed after saving.

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Managing environments

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Viewing environments

Go to Settings > Sandbox to see all your environments. Each card shows the environment name, repository, branch, and whether it’s enabled.

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Editing an environment

Click on any environment card to open the edit dialog. Changes take effect for new sessions — running sessions are not affected.

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Multiple environments

You can create environments for different projects or configurations:
  • acme/web-app — your main web application
  • acme/api — your backend service
  • acme/web-app (staging) — same repo but different branch or env vars
When starting a session, select which environment to use from the environment picker.

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Preview URLs

When you configure a run script and preview port, Magnet starts your dev server in the sandbox and gives you a URL to access it. This lets you:
  • See your app running live as the agent makes changes
  • Test the agent’s work before merging the PR
  • Share the preview with teammates for review
The preview URL is active for the duration of the session.