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smolvm sandbox port lets your host reach a service running inside a sandbox. Use it for dev servers, local APIs, databases, and preview apps.

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Synopsis

Port forwards bind to 127.0.0.1. They are reachable from your host, not from other machines on your network.

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Shared options

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--ssh-key
string
Path to an SSH private key when SmolVM needs SSH for the forward.
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--ssh-user
string
default:"root"
SSH user when SmolVM needs SSH for the forward.
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--comm-channel
string
Control channel for setup calls. Use ssh, vsock, or omit it for auto-selection.
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--json
flag
Print a JSON envelope instead of formatted text.

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expose

Share a sandbox port on localhost:
Let SmolVM pick the host port:
The mapping format is:

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list

Show active forwards:

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close

Close a forward:

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Common workflow

Open http://127.0.0.1:3000 from your host browser.

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Transports

SmolVM chooses the best forwarding transport for your host:
  • nftables when the host can route directly to the guest.
  • ssh_tunnel when a background SSH tunnel is the safest path, such as on macOS.
You do not need to choose the transport yourself.
Last modified on June 24, 2026