Mask the personal data
in your spreadsheet
Upload a CSV or Excel file, choose the columns that hold sensitive information, and lock them behind a passphrase. The output keeps its original shape, so emails still read like emails and phone numbers still read like phone numbers. When you need the real values back, upload the file again with the same passphrase and unmask it.
To unmask, use the exact same passphrase and select the same columns you masked. A different passphrase or a different set of columns will produce different values. If you lose the passphrase, the data cannot be recovered.
How it works
- Private by design. Your file is read and transformed inside the browser. It is never sent to a server, so it stays on your machine.
- Keeps its shape. Digits stay digits and letters stay letters, so a masked value looks just like the original and the file still opens cleanly.
- Fully reversible. Masking is driven by your passphrase. The same passphrase brings back the exact original values, even on a copy you have edited.
- Nothing to keep track of. The masked value carries everything needed to reverse it, so there is no separate key file or lookup table.
Frequently asked questions
Is my spreadsheet uploaded to a server?
No. The file is read and processed entirely in your browser. Nothing is sent anywhere, and you can confirm it in your browser's network tab.
Can I unmask the data later?
Yes. Re-upload the masked file, select the same columns, enter the same passphrase, and choose Unmask. The original values come back exactly.
Does it still work if I edit the sheet after masking?
Yes. Each value is masked on its own and in a repeatable way, so adding, removing, or editing rows does not stop you from unmasking the rest.
Which file formats are supported?
CSV, XLSX, XLS, and TSV. The download keeps the same format as the file you uploaded.
What happens if I lose the passphrase?
The data cannot be recovered. The passphrase is the only key and it is never stored, so keep it somewhere safe.