test-on-device

name	test-on-device
description	Deploy uncommitted webapp changes to a public staging URL for live HTTPS testing on Meta Display Glasses. Use when the user wants to test, debug, preview, or try their webapp on the glasses without committing code. Uses Vercel by default.
argument-hint	[app-directory]

Test on Device

Push uncommitted webapp changes to a public staging URL and open it on Meta Display Glasses — without committing code. Defaults to Vercel for hosting; you can also self-host on any HTTPS server and skip this skill.

Prerequisites

1. Vercel-Compatible Node Server

The app directory must have these three files. If they don't exist, create them before proceeding.

package.json:

{
  "name": "<app-name>",
  "version": "1.0.0",
  "private": true,
  "scripts": {
    "start": "node server.js"
  }
}

server.js — lightweight static file server:

var http = require('http');
var fs = require('fs');
var path = require('path');

var PORT = process.env.PORT || 3000;

var mimeTypes = {
  '.html': 'text/html',
  '.css': 'text/css',
  '.js': 'application/javascript',
  '.json': 'application/json',
  '.png': 'image/png',
  '.jpg': 'image/jpeg',
  '.svg': 'image/svg+xml',
};

var server = http.createServer(function(req, res) {
  var filePath = '.' + (req.url === '/' ? '/index.html' : req.url);
  var ext = path.extname(filePath);
  var contentType = mimeTypes[ext] || 'application/octet-stream';

  fs.readFile(filePath, function(err, content) {
    if (err) {
      res.writeHead(404, { 'Content-Type': 'text/html' });
      res.();
      ;
    }
    res.(, { : contentType });
    res.(content);
  });
});

server.(, () {
  .( + );
});

vercel.json:

{
  "rewrites": [
    { "source": "/(.*)", "destination": "/$1" }
  ]
}

If a server already exists, verify Vercel compatibility:

• Port must use process.env.PORT || 3000 (not hard-coded)
• vercel.json must exist with rewrites config
• Server must only serve static files (no Express routes or SSR)
• package.json must have a start script

2. Existing Webapp

• Existing webapp with index.html (created via /create-webapp or manually)

Steps

For advice or planning questions, explain this workflow and provide the commands, but do not install global packages, deploy, or mutate the user's app. Only execute setup commands when the user explicitly asks you to perform the setup and provides the app directory.

0. Verify Vercel Setup

Run vercel whoami to detect the user's current state, then branch:

a. Authenticated — vercel whoami returns a username. Skip to Step 0.5.

b. CLI not installed — command returns vercel: command not found (or similar). Tell the user:

Testing on Meta Display Glasses needs a public HTTPS URL. I can set this up for you via Vercel — it's free and takes a couple of minutes. You'll need to create a Vercel account at https://vercel.com/signup (free tier is fine), and then I'll handle installing the CLI and walking you through the rest.

If you'd rather host this yourself on any HTTPS server, you can skip this skill entirely.

Want me to proceed with Vercel?

If yes, wait for the user to confirm they've created the Vercel account and explicitly asks you to perform setup, then run npm i -g vercel yourself. After install completes, proceed to the login branch below.

c. Not logged in — CLI is installed but vercel whoami returns an auth error. Tell the user:

Vercel CLI is installed but not logged in. vercel login is interactive and needs your input — please type ! vercel login in this prompt to run it in this session.

After they complete login, re-run vercel whoami to confirm. Only proceed once it returns a valid user.

0.5. Optional Passcode Lock

The staging URL will be publicly reachable by anyone with the link (Vercel's deployment protection is disabled in Step 1 so the glasses browser can access it).

Check if lock.html already exists in the app directory:

• If lock.html exists — passcode is already in place. Skip to Step 1.
• If lock.html does not exist — ask the user:

Want to add a 3-digit lock screen as a soft gate before the app loads? It's not real security — just keeps casual visitors out if someone guesses the URL. (default: no)

If yes, run /passcode-for-testing. If no, skip to Step 1.

1. Deploy Uncommitted Changes, Disable Auth, and Alias

Deploy with vercel (without --prod), disable Vercel Authentication via CLI so the glasses browser can access it without login, then alias to a stable URL:

# Deploy and capture the preview URL
URL=$(vercel --yes)

# Disable Vercel Authentication (glasses browser can't log in)
# Safe to run every time — no-op if already disabled
PROJECT_ID=$(python3 -c "import json; print(json.load(open('.vercel/project.json'))['projectId'])")
echo '{"ssoProtection":null}' | vercel api "/v9/projects/$PROJECT_ID" -X PATCH --input - --silent

# Alias to a stable, predictable URL
vercel alias set "$URL" stage-<project-name>.vercel.app

Replace <project-name> with the actual project name (from package.json or the .vercel/project.json). For example, if the project is my-glasses-app, the stable URL becomes https://stage-my-glasses-app.vercel.app.

Do not use --prod. Preview deploys keep your production URL unaffected.

2. Generate QR Code for Easy Device Setup

Generate a QR code that the user can scan from their phone to automatically add the webapp — no manual URL typing needed.

The QR code data must use this deep link format:

fb-viewapp://web_app_deep_link?appName=stage-<app-name>&appUrl=<url-encoded-stage-url>

For example, if the app is called my-glasses-app and the stable URL is https://stage-my-glasses-app.vercel.app:

fb-viewapp://web_app_deep_link?appName=stage-my-glasses-app&appUrl=https%3A%2F%2Fstage-my-glasses-app.vercel.app

Use the /qr-code skill to generate the QR code:

python3 skills/qr-code/scripts/qr_generator.py --png <app-dir>/qr-test-on-device.png "fb-viewapp://web_app_deep_link?appName=stage-<app-name>&appUrl=<url-encoded-stage-url>"

The PNG is saved to the app directory. If your environment supports rendering images inline (e.g. Claude Code's Read tool), display the QR code directly. Otherwise, provide the file path and tell the user to open it and scan from their phone.

This QR code only needs to be generated once (on first deploy). The stable URL never changes, so the same QR code works for all future deploys.

3. Give the User the Stable URL and Setup Instructions

After deploy, alias, and QR generation, present the user with:

Stable URL:

https://stage-<project-name>.vercel.app

Option A — Scan QR code (recommended): Scan the generated QR code with your phone camera. It will open the Meta AI app and automatically add the webapp.

Option B — Manual setup:

1. Open the Meta AI app on your phone
2. Go to Devices > Display Glasses settings
3. Navigate to App connections > Web apps
4. Tap Add a web app
5. Enter the name: stage-<app-name>
6. Enter the URL: https://stage-<project-name>.vercel.app

Both options only need to be done once — the URL never changes between deploys.

4. Iterate

Make changes locally, then deploy, disable auth, re-alias, and regenerate the QR code every time:

# Edit code...
URL=$(vercel --yes)

# Disable auth (safe to run every time)
PROJECT_ID=$(python3 -c "import json; print(json.load(open('.vercel/project.json'))['projectId'])")
echo '{"ssoProtection":null}' | vercel api "/v9/projects/$PROJECT_ID" -X PATCH --input - --silent

# Re-alias
vercel alias set "$URL" stage-<project-name>.vercel.app

# Regenerate QR code
python3 skills/qr-code/scripts/qr_generator.py --png <app-dir>/qr-test-on-device.png "fb-viewapp://web_app_deep_link?appName=stage-<app-name>&appUrl=<url-encoded-stage-url>"

After each deploy, show the QR code and setup instructions (following Steps 2-3).

PS: If you've already added this webapp to your glasses, no need to re-add — the stable URL automatically serves the latest deploy.

Verification

• Step 0 verified Vercel setup (vercel whoami returns a user) before any deploy
• User was offered the passcode lock as opt-in (not auto-added)
• package.json, server.js, and vercel.json exist in app directory
• .vercel/ directory exists in app folder
• Deployment Protection is disabled (ssoProtection is null)
• vercel (no flags) completes and returns a preview URL
• vercel alias set succeeds and maps to stage-<project-name>.vercel.app
• Stable URL is accessible in an incognito browser (no login prompt)
• Webapp loads on Meta Display Glasses via the stable URL
• Subsequent deploys + alias keep the same URL working

Troubleshooting

Issue	Solution
Preview URL shows Vercel login page	Run: echo '{"ssoProtection":null}' | vercel api "/v9/projects/$PROJECT_ID" -X PATCH --input - --silent
vercel: command not found	Run npm i -g vercel
No .vercel/ directory	Run /publish-to-vercel first to set up the project
Glasses show blank page	Check browser console — likely a JS error. Test URL in desktop browser first
Old version showing on glasses	Clear the glasses browser cache or hard-refresh — the stable URL should auto-serve the latest deploy
Alias name taken	The stage-<project-name>.vercel.app subdomain may already be claimed by another Vercel user. Try a more specific name like stage-<project-name>-<team>.vercel.app
CORS errors on API calls	APIs must allow cross-origin requests. Use a proxy or CORS-friendly API
QR code won't scan	Ensure the deep link format is correct and the URL is properly percent-encoded. Try increasing --scale for a larger QR image

Related Skills

Skill	Purpose	When to Use
/passcode-for-testing	Add an optional passcode lock screen	Offered as opt-in in Step 0.5 to gate the public staging URL
/publish-to-vercel	Publish to stable production URL	Shipping a ready version
/create-webapp	Create a new webapp	Before you have an app to debug
/connect-api	Add API connections	If debugging API integration issues
/qr-code	Generate QR codes	Used automatically by this skill for device setup