Use ChatGPT on a spreadsheet, without sending it your customers.

Ask AI about a table without handing it over

A customer list or an aged debt report is exactly what people want help with, and exactly what should not be pasted into a chat. Press Safe for AI on the Home tab:

1. Choose Use the selection, or Use the whole sheet. The pane lists every name, email address, phone, card and account number it found, each with the placeholder it will use. Untick any that can stay.
2. Say what you want, for example "which customers are more than 60 days late, and how much do they owe in all?", and open ChatGPT or Claude with the table in it, or copy it. The AI sees [NAME_1] and [EMAIL_1], never the real details.
3. Paste the answer back into the pane and press Put the details back. The real names and numbers return in place of the placeholders.
4. Press Put it in a new sheet. The answer goes into a sheet of its own, with a table split into columns, so your own cells are never overwritten.

The request asks the AI to return tables with one row a line and tab-separated columns, which is what lets the answer land in cells. A markdown table from a chat works too. Anything in the answer that Excel would run as a formula goes in as plain text.

Check AI-written text in cells

Product descriptions and ad lines are often written with AI in a column, one per row. Check reads the selection or the whole sheet with the same rules as the site's own tools:

• Phrases that sound machine-made, such as "Certainly" and delve, as the Robot-Speak Checker finds them.
• Claims to check: cells with a number, a date, a quote or a named source, riskiest first, as in the Fact Check List.
• Blanks the AI left, such as [insert date], which are easy to miss in row 400.
• Private details: email addresses or account numbers that should not go out.

In current versions of Excel, click a finding and Excel selects its cell. It reads up to 20,000 cells at a time, from the top of the sheet.

Score a prompt kept in a sheet

Teams that keep their prompts in a spreadsheet can select one and open Prompt: it is scored out of 10 on the ten checks, with the questions the AI would otherwise guess at, and Write a better prompt rebuilds it as the Prompt Improver does.

How to add it

Until it is listed in Microsoft AppSource, Excel adds it from a small file that tells Excel where the add-in lives.

1. Download the add-in file (manifest-excel.xml).
2. Open a workbook in Excel on the web, at office.com.
3. On the Home tab choose Add-ins, then More Add-ins. In the window that opens, choose My Add-ins, then Upload My Add-in, and pick the file. The wording can differ slightly between versions of Excel.
4. Safe for AI appears on the Home tab. Press it to open the pane.

At work, your IT team can add it for everyone at once from the Microsoft 365 admin center (Settings, Integrated apps, Upload custom apps) with the same file. That is also how it reaches Excel on Windows and Mac before the AppSource listing.

Private by design

Every check runs in the pane, inside Excel. The add-in sends nothing in your workbook to thinkhard.si or anyone else and stores nothing. It reads cells only when you press a button, and it changes the workbook only when you ask, by adding a new sheet. A table goes to ChatGPT or Claude only when you press their button, with the placeholders in place of the details you kept ticked. The full detail is in the privacy policy.