CloakScan

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[!WARNING] Not in the Chrome Web Store yet. This is the working prototype, loadable unpacked. The detectors are tested against a fixture page in headless Chromium. Try them in the live demo; the store package is next on the roadmap.

💡 What it's for

If you hand pages to an agentic browser or paste them into a chatbot, the page can carry instructions meant for the model and hidden from you: white text on a white background, a div parked 9,999 pixels off-screen, a 1px font, an HTML comment. Brave showed attackers doing exactly this to Perplexity's Comet. CloakScan reads the tab you're on, outlines each piece of hidden text on the page, and lists what it found in plain language. Then it can copy the page's visible text with the hidden parts stripped, so you paste only what you actually read.

It runs when you click it and at no other time. There's no host_permissions entry, no background script, and nothing leaves your browser.

📊 What it detects

Technique	How it's spotted
Color-matched text	Contrast between the text and its nearest background under 1.15:1
Off-screen positioning	Absolutely or fixed-positioned and more than 200px outside the viewport
Shrunk to invisible	Font size of 1px or less, or a 1x1 box with overflow hidden
Hidden from screen readers	aria-hidden="true" on text addressed to a model or overriding one (ADR-003)
HTML comments	Comments with the same instruction phrasing
Zero-width characters	U+200B, U+200C, U+200D, U+FEFF or U+2060 inside ordinary text

🚀 Quick start

# 1. Install dev dependencies (Node 22.2 or newer)
npm install

# 2. Copy the extension into dist/extension/ and zip it into dist/cloakscan-<version>.zip for the store
npm run build

# 3. In Chrome: chrome://extensions, turn on Developer mode, Load unpacked, pick dist/extension/

# 4. Tests and lint (the detection test runs in headless Chromium, installed once)
npx playwright install chromium
npm test && npm run lint

To try it without installing anything, open src/index.html in a browser, click the CloakScan icon in the mock toolbar, then Scan this page.

🗂️ What's in here

Folder	What's inside
🧰 src/	The extension and the demo page.
📚 docs/	The roadmap, the changelog, and the product spec and build plan.
🧪 tests/	Tests for node --test. detection.test.js loads fixtures/hidden-text.html in headless Chromium through Playwright, injects content.js, and checks all six techniques come back and nothing else does, that copy-visible-only text holds none of them, and that a clean 5,000-node page scans in under 2 seconds with no findings. manifest.test.js holds the permission list to activeTab, scripting and storage and fails on any network call under src/extension/. package.test.js runs the build and checks the store zip holds exactly the extension's files, manifest.json at its root.
⚙️ .github/workflows/	CI: npm ci, lint, the tests (headless Chromium included) and the build, on every PR and every push to main.
🔒 SECURITY.md	How to report a vulnerability privately.
🛡️ PRIVACY.md	The privacy policy: nothing collected, the last scan kept on the device, nothing sent. The Chrome Web Store listing will link it.

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