Your agent.
Your first sandbox.

Runtime Cloud runs your code and your agents' code on machines we operate. Sandboxes come first: Linux microVMs with their own kernel, disk and toolchain, usually ready in under a second; startup varies with the workload and capacity. One API, one CLI, one MCP server and SDKs for JavaScript and Python cover every Runtime product. New accounts get 20 free hours with no card: see the free trial.

One line, with Node 22 or later:

Terminalnpx withruntime run --trial -- python3 -c 'print(6 * 7)'

The first time, it connects this machine: your browser opens a Runtime page (or the command prints a link and a code), you sign in with Google or an email link, check the code and choose Connect agent. Nothing to copy. Then a fresh sandbox runs the command, prints 42 and requests a stop. Check the exit code: zero means the command succeeded. Confirm cleanup with npx withruntime sandbox ls --json; if the test sandbox remains, stop it and verify its state. The explicit --trial refuses paid funding even if this account has credit. Later commands reuse the connection.

An agent running it shows you the link and code. If you approve after the command has given up waiting (it waits 50 seconds when no one is at a terminal), the agent runs it again and it finishes, with no new link.

For several commands in one sandbox, this shell block stops it on exit:

Terminal(  id=$(npx withruntime sandbox create --trial) || exit  trap 'npx withruntime sandbox stop "${id}"' EXIT  npx withruntime sandbox exec "${id}" -- python3 -c 'print(6 * 7)')

Installed with npm install --global withruntime, the command is runtime: runtime run --trial -- ls, runtime sandbox create --trial. See the CLI.

Add Runtime's MCP server to your agent with one command:

Terminalclaude mcp add --scope user runtime -- npx -y withruntime mcp   # Claude Codecodex mcp add runtime -- npx -y withruntime mcp                 # Codex

Cursor: add this to ~/.cursor/mcp.json (or .cursor/mcp.json in a project):

JSON{ "mcpServers": { "runtime": { "command": "npx", "args": ["-y", "withruntime", "mcp"] } } }

If this machine is not connected yet, the agent sees one tool, runtime_connect, which gives it a link for you to approve; then every Runtime tool appears. See MCP for other clients and the remote endpoint.

TypeScriptimport { Sandbox } from "withruntime";const sbx = await Sandbox.create({ funding: "trial" });try {  const result = await sbx.exec("python3 -c 'print(6 * 7)'", { check: true });  console.log(result.stdout);} finally {  await sbx.stop();}

Pythonfrom withruntime import Sandboxwith Sandbox.create(funding="trial") as sbx:    print(sbx.exec("python3 -c 'print(6 * 7)'", check=True).stdout)

npm install withruntime or pip install withruntime. The SDKs use RUNTIME_API_KEY when it is set, and otherwise the key this machine saved when it connected, so after the one line above they need no setup. On a server, create a key at https://withruntime.com/account/keys and give it as RUNTIME_API_KEY from your secret manager. create() needs no arguments and waits for readiness and raises start_failed if it stops before becoming ready. The examples insist on trial funding, check the command result, and stop even after an error. Export anything you need before stopping.

The browser approval gives this machine its own key, encrypted for it alone and saved outside your project: the CLI receives and saves its own credential automatically, and you do not copy an API key. Each connection can use everything the account can, including its prepaid credit, so approve only connections you started. Browser sign-out does not revoke one; npx withruntime logout or the API keys page does. See security.

On a machine with no browser, npx withruntime login --no-browser prints the link to open on another device. To use a key you already have instead, npx withruntime login --with-key reads it from standard input, never from the command line.

Trial requests never fall back to paid credit. Omitting funding can use prepaid credit after the trial is exhausted. Keep funding: "trial" for free use; choose funding: "paid" only when you intend to use credit.

Set up Runtime Cloud for this project: read https://withruntime.com/llms.txt, run npx withruntime run --trial -- echo hello, and when it prints a link, show it and the matching code to me and wait for my browser approval. Do not ask me for an API key or switch to paid credit. Check the output, exit code and cleanup. Report any blocker without exposing credentials or private files.

Keep the error code, request ID and sandbox ID. A lost response is not proof that nothing ran: inspect the original resource before trying another create. For connection_pending, approve the printed request and rerun the same command. For trial_busy or trial_exhausted, inspect your trial usage; do not add --paid without deciding to use credit. For start_failed, read the sandbox's state and stopReason; never treat a stopped sandbox as ready. See troubleshooting for safe retries and cleanup.

Keep important results outside the sandbox: a sandbox is not a backup.