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When you run a web server, database, or API inside a sandbox, port forwarding lets you access it from your host machine as if it were running locally.

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Expose a port

Start a service inside the sandbox and expose it to your host: 
from smolvm import SmolVM

with SmolVM() as vm:
    vm.run("python3 -m http.server 8000 &")

    host_port = vm.expose_local(guest_port=8000, host_port=8000)
    print(f"Service available at http://127.0.0.1:{host_port}/")
Omit host_port to let SmolVM pick an available port automatically: 
host_port = vm.expose_local(guest_port=8080)
print(f"Guest port 8080 exposed on localhost:{host_port}")

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Multiple ports

Expose multiple services from the same sandbox: 
with SmolVM() as vm:
    vm.run("python3 -m http.server 8000 &")
    vm.run("python3 -m http.server 9000 &")

    port1 = vm.expose_local(guest_port=8000, host_port=8000)
    port2 = vm.expose_local(guest_port=9000, host_port=9000)

    print(f"Service 1: http://127.0.0.1:{port1}/")
    print(f"Service 2: http://127.0.0.1:{port2}/")

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Remove a port forward

Port forwards are automatically cleaned up when the sandbox stops. To remove one manually: 
vm.unexpose_local(host_port=8080, guest_port=8080)
expose_local() only binds to 127.0.0.1 (localhost). Services are not exposed to your network.
Last modified on April 29, 2026