Guide · For accountants · ~6 min read

How to anonymize bank statements and invoices before using AI

AI is useful for categorising expenses and checking totals, but a bank statement carries your client’s name, ID number and account numbers. Here is how to analyse the month’s documents with AI without sending that data.

The problem with pasting a statement

A bank statement pasted into an AI chat carries the account holder, their ID number, email, phone and account or card to a third party. Your client trusted those to you.

Removing them by hand, document by document, does not scale during a month-end close, and something always slips through.

What gets hidden in a statement

The account holder’s name, which becomes a placeholder such as “Holder 1”.
The ID number (RUT, DNI, CPF and others from 32 countries).
Email and phone number.
Card and bank account numbers.

Amounts and dates stay. The AI reads the figure of every transaction but does not know whose they are. And the same placeholder (for example “ID 1”) always stands for the same person across all of a client’s documents.

To see what a piece of text contains first, try the free personal data detector: it runs in your browser and uploads nothing.

Step by step

Convert. Drop the bank statements, invoices and tax returns into the right client. The app converts them to text with the tables intact.
Review. You see what was hidden and what is still visible, and you hide anything left in view with one click.
Copy. You copy everything for a client as one text with your question at the end, and paste it into ChatGPT, Claude or Copilot.

The numbers add up, before the AI reads them

ContextDeck checks that a statement’s transactions add up to the billed total, and tells you before you copy. On invoices it checks that net plus tax equals the total and shows you the difference if not.

It is a pre-check, useful so you do not ask the AI to analyse a document that already contains an error.

Questions that work well

Do the net, the tax and the total add up?
Categorise the expenses for the period.
Add up the invoices: net, tax and total.

The record

Every conversion leaves a dated record of what was hidden, in which files and on which computer, without ever storing the original values.

Frequently asked questions

Can the AI still analyse the amounts if the client’s data is hidden?

Yes. Personal data is hidden, not the amounts or dates. The figures and transactions stay visible for the analysis.

Does it work for invoices as well as bank statements?

Yes. It checks that net plus tax equals the total and tells you the difference if it does not.

Is it free?

The Free plan marks personal data and checks whether statements and invoices add up (up to 3 files at a time, 30 a month), but it does not hide the data. Hiding it before you copy is part of Pro, with a 14-day trial and no card.

Does this replace compliance with data protection law?

No. 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.

Keep reading

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.

Try it on a sample document

Try Pro free for 14 days, no card. You download the Windows app and nothing is uploaded to the internet.

Download for Windows