Tunnel/expose a localhost service to the internet from inside a cloud VM — get a stable public HTTPS URL (https://<box>-<port>.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.
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Added September 7, 2026
ai-agentsgobashapi
Works with
api
Security analysis
D42/100
criticalPipes output to a shell interpreter
mediumUses curl or wget to download content
criticalDownloads and executes remote scripts — classic supply chain attack
Installs into .claude/skills of the current project.
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---
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://<box>-<port>.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
```bash
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.
