expose-localhost-tunnel - SKILL.md Agent Skill

name: expose-localhost-tunnel description: Tunnel/expose a localhost service to the internet from inside a cloud VM — get a stable public HTTPS URL (https://-.on.ascii.dev) with TLS and token-gating built in, no separate daemon or account like ngrok. The VM's dedicated IPv4 also allows raw TCP/UDP and bring-your-own domain. Use to share a preview, expose a webhook target, or open a port.

Expose / tunnel localhost (Box)

Use this when a service running in a Box must be reachable from outside: sharing a dev preview, receiving webhooks, or demoing. Because the service already runs inside the VM, exposing it is one command — no ngrok-style sidecar, no extra account, no cert setup.

Recipe

box ssh "$box_id" -- "cd /app && PORT=3000 npm start &"   # MUST bind 0.0.0.0
box ssh "$box_id" -- "host 3000 --title preview"
box ssh "$box_id" -- "host url 3000"                       # -> https://<box>-3000.on.ascii.dev?_token=...
box ssh "$box_id" -- "host list"                           # manage; host hide <port> to revoke

Ascii terminates TLS for on.ascii.dev and proxies to the box. URLs are token-gated by default (--public drops the token, --private enforces it).

Why Box beats a tunnel tool

No separate daemon/account — the route lives with the VM.
TLS + auth handled; URL stable across the box's life.
Dedicated IPv4 + full TCP/UDP — non-HTTP servers and BYO domains work; most sandbox providers can't tunnel raw TCP/UDP at all.

Prereqs

curl -fsSL https://box.ascii.dev/install | sh, then box login "$BOX_API_KEY" --json.

Gotchas

App must bind 0.0.0.0. For a URL that outlives a long session, pair with box extend <id> --no-auto-stop. EU-only region today.