Hiding personal data before using AI: a local app or a browser extension?

The short answer

If you only paste short pieces of text into one chat tool, a browser extension can be enough. If you work with files (PDF, Word, Excel, scans) or with several AI tools, hiding the data on your own computer before anything reaches an AI is the more reliable approach, because it does not depend on which website or app you paste into.

The three approaches

• A browser extension on the AI page. It watches what you paste or upload on that site and offers to hide personal data first. Easy to start, but it only covers the sites it supports, and an extension asks for permissions on the pages you visit: read them before installing.
• A paste or clipboard tool. You copy text, run the tool, and paste the cleaned result. Works anywhere you can paste, but it is manual and normally handles text, not files.
• Converting and hiding on your PC before any AI. A desktop app converts the document to text, hides the data, and shows you the result before you copy it. It handles files and does not depend on the AI site. It costs more setup than an extension, and it is one more app to install.

Six questions to choose

1. What are you sending? Short text, or whole files such as contracts, bank statements, invoices and scans?
2. Where does the detection run? On your computer, or on a server? If it is a server, your document has already left.
3. Can you see what was hidden and what is still visible? Detection is never perfect. You need to review the result before you send it.
4. Does it work with every AI you use, including desktop apps and tools that are not in a browser?
5. Is there a record of what was hidden and when, in case a client or your firm asks?
6. What does it do with names? Many tools find numbers (IDs, cards, emails) better than a name inside a sentence.

Where ContextDeck fits

ContextDeck Docs is the third approach. It is a Windows app that converts PDF, Word, Excel and PowerPoint (with Pro also whole folders, scanned PDFs and photos) into text and hides personal data on your computer before it reaches ChatGPT, Claude or Copilot. Nothing is uploaded to the internet.

It hides ID numbers from 32 countries (including RUT, DNI, NIE, CURP, RFC, CPF, CUIT and NIT), emails, phone numbers, cards and bank accounts. You add your clients’ and companies’ names once. It shows what was hidden and what is still visible, and keeps a dated record without the original values.

What it does not do

• It does not recognise a name inside a paragraph by itself. That is why the review before you copy is part of the process.
• The free plan marks personal data but does not hide it, and is limited to 3 files at a time and 30 a month. Hiding before copying is part of Pro ($9 per month or $86 per year, with a 14-day trial and no card).
• It runs on Windows 10 and 11 only.
• It reduces the risk of exposing personal data. It is not legal advice and does not replace the review your jurisdiction requires.

Try it on a sample first

Whatever approach you choose, test it on a dummy document with an email, a phone number, a card number, an IBAN and a national ID before using it on a client file. You can see how detection works on short text with the free personal data detector, which runs in your browser and uploads nothing.

Related guides

For contracts, read how to use ChatGPT with client contracts. For statements and invoices, read how to anonymize bank statements before using AI. For a list of what to hide, read what personal data to hide before pasting into an AI.

Frequently asked questions

Is a browser extension enough for client documents?

It can be for short pasted text on a site it supports. For files, scans or several AI tools, check what it covers and where its detection runs before relying on it.

Why does it matter where the detection runs?

If the document is sent to a server to be checked, it has already left your computer. A tool that runs locally avoids that step.

Does hiding names work automatically?

Not reliably in any tool. Numbers such as IDs, cards and emails follow patterns and are easier to find. Names inside a sentence are harder, so review the result before you send it.

Does this make me compliant with privacy law?

No tool guarantees compliance. Hiding data reduces the risk of exposing it and a record helps you show what you did, but it is not legal advice and does not replace your own jurisdiction’s review.

ContextDeck reduces the risk of exposing personal data when you use AI and keeps a record of what you did. It is not legal advice and does not replace the legal review your own jurisdiction requires.