The problem: your personal data ends up with AI providers
Do you use ChatGPT, Claude, Gemini or Copilot at work? You have probably already pasted a contract, a client email, minutes of a meeting or an invoice containing names, IBANs, national register numbers or addresses directly into the chat.
The problem is simple: this personal data is sent to the AI provider. Even if some promise not to train their models on your data, the transfer takes place, the data is processed, and you have no guarantee about what actually happens to it.
For lawyers, DPOs, doctors, accountants and all professionals bound by professional secrecy, this is a major risk — both in terms of professional ethics and GDPR compliance.
The solution: pseudonymise BEFORE the data reaches the chat
PseudoShield is a free and open source browser extension (MIT licence) that intercepts pasting (Ctrl+V) on AI platforms and automatically replaces personal data with deterministic pseudonyms (SHA-256) before the text is inserted into the interface.
In practice, when you paste text containing:
Jean-Pierre Dupont → [Person_13]
85.03.15-123.45 → [NISS_1]
BE68 5390 0754 7034 → [IBAN_1]
jp.dupont@cabinet.be → [Email_3]The AI works on the pseudonymised text. You keep the mapping table locally on your machine. Simple, effective, and without any data leaving your browser.
Features
35 detection patterns
The extension automatically detects a wide range of personal data: proper names (4 detection strategies), Belgian NISS numbers, IBANs from 7 countries, VAT numbers, BCE numbers, INAMI numbers, email addresses, phone numbers, postal addresses, bank card numbers, IP addresses, GPS coordinates and social media handles.
Mathematical validation
PseudoShield does not rely on regex alone: identifiers are validated mathematically. Modulo 97 for NISS, IBAN and INAMI numbers. Luhn algorithm for bank cards. ISO 13616 standard for IBANs. This significantly reduces false positives.
6 supported platforms
The extension works on the main AI chat interfaces: Claude.ai, ChatGPT, DeepSeek, Gemini, Copilot and Perplexity.
100% local
Zero network calls, zero user accounts, zero telemetry. Processing is done entirely in your browser via the Web Crypto API. No data ever leaves your machine.
Built-in GDPR compliance
The extension includes several compliance features:
- Pseudonymisation as defined in Article 4(5) of the GDPR — note that pseudonymised data remains personal data
- Audit log compliant with Article 30 (CSV/JSON export)
- Automatic categorisation according to Article 4 (personal data) and Article 9 (sensitive data)
- Mapping table accessible locally
A word of transparency
This project contains a significant amount of vibecoding — code generated with AI assistance. The extension works well for the vast majority of use cases, but some imperfections remain, particularly in postal address detection which can still produce false positives or misses.
Your feedback is invaluable for improving the tool. If you notice any unexpected behaviour, please open an issue on GitHub or contact me directly.
Install PseudoShield
The extension is available for free on the two main stores:
- 🟢 Google Chrome: Install from the Chrome Web Store
- 🦊 Mozilla Firefox: Install from Firefox Add-ons
- 💻 Source code (MIT): View on GitHub
Who is PseudoShield for?
The extension is particularly useful for professionals who handle personal data on a daily basis and want to use AI without compromising confidentiality: lawyers, notaries, DPOs, doctors, pharmacists, human resources professionals, accountants, auditors, social workers — and more generally anyone bound by an obligation of professional secrecy or confidentiality.
PseudoShield is an open source project developed by Lawgitech. Questions, suggestions or bugs to report? Open an issue on GitHub or contact us at info@lawgitech.eu.