A cloud box is a Linux container spacesheep runs for the person, with Claude Code, Codex or Antigravity and sessionpipe in it: nothing to install, it sleeps 10 minutes after its last reply and wakes for the next message (about 30 s), and its session shows on spacesheep.dev/sessions like one on their own computer. It has spacesheep's MCP server and /sheep skill, so pages it makes are spaces. It comes with Max. The agent runs on the person's own account with its maker — Claude (Pro or Max), ChatGPT or Google, signed in once on the box's page in the agent's own sign-in — or on their own key (ANTHROPIC_API_KEY, OPENAI_API_KEY or GEMINI_API_KEY; Settings → AI assistant or set_secret). A GITHUB_TOKEN reaches only the box's own repos (up to 5 per box). YOLO mode (yolo: true) lets Claude Code run without permission checks and merge pull requests; off, it opens pull requests and merging is refused. A box on a key reaches the model API, GitHub, spacesheep and the package registries, nothing else. Start a NEW box, and its first turn when `prompt` is given: the agent works on it (in clones of `repos` when given, each in its own folder). Answers at once with the box, its session and session_url — send the person session_url — then read progress and the reply with list_boxes. A box on a Claude account answers with `sign_in`: the person signs in on session_url first, and messages wait until then — tell them so. Use only when the person asked for work on a cloud box / a new machine / "in the cloud"; to continue a box's work, use message_box.