PasteGuard

Paste into AI. Keep the secrets.

A free Chrome extension that masks emails, phone numbers, card numbers, API keys and client names the moment you paste into ChatGPT, Claude or Gemini. Then it shows you the real values in the AI's reply. Everything runs locally.

🌐 Website + live demo · 🧩 Add to Chrome · Privacy policy

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Why

People paste client emails, support tickets, spreadsheets and code into AI chat tools every day. Those pastes are full of names, emails, phone numbers, card numbers and API keys that shouldn't leave the company. Blocking AI tools doesn't work, and enterprise security tools are priced for large companies.

PasteGuard is a seatbelt: it's invisible until it's needed, and it doesn't change how you work.

How it works

You paste:     Priya Shah ([email protected]) says card 4111 1111 1111 1111 was charged twice
AI receives:   [PERSON_1] ([EMAIL_1]) says card [CARD_1] was charged twice
AI replies:    Hi [PERSON_1], we've refunded the duplicate charge on [CARD_1]…
You see:       Hi Priya Shah, we've refunded the duplicate charge on 4111 1111 1111 1111…

1. Catch. It reads the clipboard text in the paste event, before the chat box gets it.
2. Mask. Sensitive values become stable placeholders. The same value always gets the same placeholder, so the AI's answer stays coherent.
3. Restore. When the reply mentions a placeholder, the real value is swapped back on your screen only and highlighted. The text box you type in is never touched.

What it detects

25 detectors in three layers. Everything runs locally; no AI model is involved.

1. Patterns with checksums

Detector	Example	Validation
Card number	4111 1111 1111 1111	Luhn checksum
IBAN	DE89 3704 0044 0532 0130 00	Mod-97 checksum
Aadhaar	2341 2341 2346	Verhoeff checksum
PAN, GSTIN, IFSC, UPI ID	ABCPE1234F, 27ABCDE1234F1Z5, HDFC0001234, name@okicici	Format
US SSN	123-45-6789	Excludes invalid ranges
Email, phone, IP address	+91 98765 43210, 10.24.8.112	Digit counts, octet ranges; ignores dates, amounts, versions
API keys	OpenAI, Anthropic, Stripe, AWS, GitHub, GitLab, Slack, Google, Hugging Face, Groq, xAI, SendGrid, Shopify…	Known prefixes
JWTs, private keys, crypto wallets	eyJ…, -----BEGIN PRIVATE KEY-----, 0x71C7…	Structure
Unknown secrets	Q7mZp3Xc9LkT2vBn8RwY4hJd6FsGa1Ue	Entropy check; skips hashes, UUIDs and variable names

2. Context: the words around a value

Detector	Catches
Passwords / secrets	password: …, DB_PASSWORD=…, postgres://user:PASS@host, ?token=…
Card CVV / expiry	CVV 123, expiry 12/29
PIN / OTP	OTP is 482913
Date of birth	DOB: 14/08/1991
ID numbers	client ID HLX-00482, study ID ONC-2026-0117, IRB approval number IRB-77421, account number …, passport …
Names	Dr. Ananya Rao, finance officer Rohan Deshmukh, Name: Rahul Verma, Hi Priya, common first + last names
Addresses	21 Research Park Road, Cambridge, MA 02139, Flat 4B, 12 MG Road, Bengaluru 560001
Organisations	Helix Biosciences Inc., … Labs, … Technologies
Project codenames	Project Aurora, Operation …

3. Inference and propagation

• [email protected] → also masks Priya Shah and Northwind wherever they appear
• Once Helix Biosciences Inc. is found, a later bare Helix is masked too
• Your own terms: Acme Corp => CLIENT in the popup

Checksums and context keep false alarms low: order numbers, invoice numbers, dates, money, version numbers, commit hashes and UUIDs are left alone. See dev/test-detectors.js.

Works on: ChatGPT, Claude, Gemini, Microsoft Copilot, Perplexity, DeepSeek, Mistral Le Chat, Poe.

Install

Add PasteGuard to Chrome → One click, free, updates automatically. Works in Chrome, Edge, Brave and Arc.

Manual install (for developers):

1. Download pasteguard-extension.zip and unzip it.
2. Open chrome://extensions and switch on Developer mode.
3. Click Load unpacked and select the unzipped pasteguard folder.
4. Pin the 🛡️ icon, then paste something sensitive into ChatGPT.

Privacy

• No servers. There's no backend. The extension makes no network requests.
• Memory-only vault. The placeholder → value map lives in chrome.storage.session, which is wiped when the browser closes.
• One permission: storage. It runs only on the AI chat sites listed above.
• No analytics. Usage stats (counts only, never values) stay on your device and are shown only in the popup.

Full policy: PRIVACY.md

Project structure

extension/
  manifest.json    Manifest V3; storage permission only
  detectors.js     Detection engine: regex + checksum validators, mask/restore
  content.js       Paste interception, toast, restore-in-replies (CSS Highlight API)
  background.js    Defaults, session-vault access, toolbar badge
  popup.html/.js   Stats, session vault, custom terms, detector toggles
index.html         Website + live playground (uses the same detectors.js)
dev/               Test harnesses for the content script and popup
STORE-LISTING.md   Chrome Web Store submission copy

Product notes

Target user	Knowledge workers who use AI daily with client data: consultants, support, recruiters, finance, lawyers
North-star metric	Sensitive values masked per weekly active user
Guardrails	False-positive rate (masks the user overrides with "Allow next paste"), uninstall rate
Business model	Free for individuals → Pro ($5/mo: typed text, file uploads, any site) → Team ($6/user/mo: shared rules, admin dashboard, audit log)

Roadmap

• Chrome Web Store listing: live
• Mask typed text before send, not just pastes
• Scan file uploads (PDF, DOCX, CSV) before they reach the AI
• Per-site enable/disable
• Team tier: shared term lists, managed deployment, admin dashboard

Limitations

• Names are detected from context and common first names. Unusual names with no context clue can slip through, so add them to Always mask.
• v0.1 masks pastes, not typed text or file uploads.
• It's a safety net, not a guarantee. Don't rely on it as your only control for regulated data.

Development

No build step. Edit the files and click reload on chrome://extensions.

• node dev/test-detectors.js runs the detection regression suite (-v prints the masked text)
• dev/harness.html runs content.js against a fake chat page with a chrome.* shim
• dev/popup-harness.html renders the popup with sample data

Serve the repo root with any static server (for example npx serve .) and open those pages.

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MIT licensed · Built by Aayush Mehan