Modal Sandboxes

Disposable remote containers (with optional GPU) via Modal, paid per call in USDC. No Modal account, no GPU procurement — pay only for what runs.

How to Call from MCP

// 1. Create
blockrun_modal({ path: "sandbox/create", body: {
  image: "python:3.11",
  gpu: "A100",
  timeout: 600,
  setup_commands: ["pip install torch transformers"]
}})
// returns { sandbox_id, ... }

// 2. Exec
blockrun_modal({ path: "sandbox/exec", body: {
  sandbox_id: "sb_abc...",
  command: ["python", "-c", "import torch; print(torch.cuda.get_device_name(0))"]
}})

// 3. Terminate
blockrun_modal({ path: "sandbox/terminate", body: { sandbox_id: "sb_abc..." } })

Endpoint Catalog

Field Reference

Worked Examples

1. Quick Python eval

const { structuredContent: sb } = await blockrun_modal({ path: "sandbox/create", body: {} })
await blockrun_modal({ path: "sandbox/exec", body: {
  sandbox_id: sb.sandbox_id,
  command: ["python", "-c", "import numpy; print(numpy.__version__)"]
}})
await blockrun_modal({ path: "sandbox/terminate", body: { sandbox_id: sb.sandbox_id } })

Cost: $0.012 ($0.01 + $0.001 + $0.001).

2. GPU inference, A100, with deps pre-installed

blockrun_modal({ path: "sandbox/create", body: {
  image: "pytorch/pytorch:2.4.0-cuda12.1-cudnn9-runtime",
  gpu: "A100",
  timeout: 1200,
  memory: 16384,
  setup_commands: ["pip install --quiet transformers accelerate"]
}})

Then sandbox/exec with your inference command. Sandbox auto-evicts after 1200s idle.

3. Test untrusted code Claude generated

blockrun_modal({ path: "sandbox/exec", body: {
  sandbox_id,
  command: ["bash", "-c", "<the generated script>"],
  timeout: 60
}})

Output is captured. No risk to your local machine.

When NOT to Use Modal

• Normal repo edits / dev work — use local tools, Modal adds latency and cost
• Long-running services — sandboxes are ephemeral, not server hosts
• Anything you'd run hundreds of times per minute — payment overhead dominates at high QPS

Notes

• sandbox_id is returned by create and required by every other endpoint
• exec is sync — blocks until command finishes or hits its timeout
• terminate is cheap; call it to free the sandbox even if timeout would expire shortly
• The free-tier nvidia/* LLM models in blockrun_chat are different infrastructure — Modal is for your arbitrary code

Reference

• Endpoints: POST /v1/modal/sandbox/{create,exec,status,terminate}
• Upstream: Modal