Expose Localhost

Expose Localhost

Expose a local service to the public internet using ngrok. Optionally add OAuth, OWASP protection, or rate limiting via Traffic Policy.

Prerequisites

• ngrok CLI installed (ngrok command available)
• Auth token configured (ngrok config add-authtoken )

Workflow

Step 1: Pre-flight & Configuration

Silently verify ngrok is ready:

ngrok config check

If auth token missing, tell user to run: ngrok config add-authtoken (get token at https://dashboard.ngrok.com/get-started/your-authtoken)

Then ask all questions upfront before doing anything:

Before I expose your service, I need a few details:

1. **Port**: I see your app runs on port 3000. Is that correct?
2. **Domain**: Use your dev domain, or do you have a custom domain?
3. **Access control**: Open access, or require login (Google/GitHub/etc.)?
4. **Save config?**: One-time setup, or save for reuse?

Do NOT mention cloud endpoints, reserved domains, or internal endpoints — those are advanced concepts the user shouldn't need to think about.

Detecting the port: Check package.json scripts for --port, .env for PORT=, docker-compose.yml for port mappings.

Domains: Most ngrok accounts have a free static dev domain (e.g., something.ngrok-free.dev). Running ngrok http PORT uses it automatically. Users can also provide a custom domain configured in the ngrok dashboard. Some accounts (especially new ones) may not have a dev domain yet — if ngrok fails with ERR_NGROK_15013, tell the user: "You don't have a dev domain yet. Claim your free one at https://dashboard.ngrok.com/domains — then we can try again."

If user requests OAuth, also ask: "Should only specific people be able to access it? I can restrict by email address or email domain."

After gathering answers, confirm and get a Y/n before proceeding.

Step 2: Start the Tunnel

No security (simplest)

ngrok http {PORT} &
sleep 3
curl -s http://localhost:4040/api/tunnels | grep -o '"public_url":"[^"]*"' | head -1

With a specific domain, add --url https://{DOMAIN}.

With security (Traffic Policy)

Create the traffic policy file first, then start ngrok with it.

OAuth-only (default when user requests auth):

on_http_request:
  - actions:
      - type: oauth
        config:
          provider: google

Replace google with the chosen provider (google, github, microsoft, gitlab, linkedin, twitch).

If the user requests OAuth, default to OAuth-only. Do NOT add OWASP or rate limiting unless explicitly asked — OAuth already blocks unauthenticated access.

OAuth with email restriction — use a separate rule with a CEL expression to deny non-matching emails. Do NOT add an allow field to the OAuth action.

Single email:

on_http_request:
  - actions:
      - type: oauth
        config:
          provider: google
  - expressions:
      - "actions.ngrok.oauth.identity.email != 'user@example.com'"
    actions:
      - type: deny
        config:
          status_code: 403

Email domain:

on_http_request:
  - actions:
      - type: oauth
        config:
          provider: google
  - expressions:
      - "!actions.ngrok.oauth.identity.email.endsWith('@your-company.com')"
    actions:
      - type: deny
        config:
          status_code: 403

Multiple emails — use !(... in ['a@x.com', 'b@x.com']) in the expression.

Open-access hardening (no auth, but wants protection):

on_http_request:
  - actions:
      - type: rate-limit
        config:
          name: default-rate-limit
          algorithm: sliding_window
          capacity: 200
          rate: "60s"
          bucket_key:
            - conn.client_ip
      - type: owasp-crs-request
        config:
          on_error: halt

on_http_response:
  - actions:
      - type: owasp-crs-response
        config:
          on_error: halt

After writing the policy file, start ngrok:

ngrok http {PORT} --traffic-policy-file .ngrok/traffic-policy.yml &
sleep 3
curl -s http://localhost:4040/api/tunnels | grep -o '"public_url":"[^"]*"' | head -1

Add --url https://{DOMAIN} if using a specific domain.

Step 3: Handle Errors

If a traffic policy action fails due to plan limitations:

1. Tell the user which specific action requires an upgrade
2. Offer to remove that action from the policy and retry
3. Do NOT suggest switching to cloud endpoints as a workaround

Step 4: Persistent Configuration (If Requested)

Save these files to the project:

• .ngrok/traffic-policy.yml — the policy (if security was configured)
• .ngrok/expose.sh:

#!/bin/bash
set -e
echo "Your service will be at: https://{DOMAIN}"
ngrok http {PORT} --url https://{DOMAIN} --traffic-policy-file .ngrok/traffic-policy.yml

Omit --traffic-policy-file if no policy. Omit --url if no specific domain.

Optionally add to package.json:

{ "scripts": { "tunnel": "bash .ngrok/expose.sh" } }

Teardown

pkill ngrok

Cloud Endpoints (Advanced)

Only use if the user explicitly needs a URL that persists after the agent stops (e.g., webhooks, long-lived integrations).

Requires an API key: ngrok config add-api-key (get at https://dashboard.ngrok.com/api-keys)

1. Reserve domain: ngrok api reserved-domains create --domain "{DOMAIN}"
2. Create cloud endpoint with a traffic policy that includes forward-internal as the last action:

ngrok api endpoints create --url "https://{DOMAIN}" --bindings public --traffic-policy "$(cat .ngrok/traffic-policy.yml)"

The traffic policy must end with:

- type: forward-internal
  config:
    url: https://{NAME}.internal

1. Start the internal agent: ngrok http {PORT} --url https://{NAME}.internal
2. Teardown: ngrok api endpoints delete {ENDPOINT_ID}

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: ngrok
• Source: ngrok/agent-skills
• License: MIT

Install and usage instructions live in the source repository linked above.