Last updated: 26 September 2026
Excel PII Masker does not collect, transmit, or store any of your data on any server. There is no backend. Everything the extension does happens inside your own browser, on your own computer.
When you open a file with this extension, it reads the file in order to detect personal information and replace it with placeholders.
| Data | Where it goes | How long it is kept |
|---|---|---|
| The file you open | Held in browser memory only | Discarded when you close the side panel, lock the vault, or load another file. It is never written to disk. |
| The values that were masked | Stored encrypted on your computer, so masked files can be reversed later | Until you delete them or remove the extension |
| Your passphrase | Never stored anywhere | Held in memory only while you are using the extension |
| Settings | Stored locally in your browser | Until you remove the extension |
The values behind each placeholder are encrypted with AES-256-GCM using a key derived from your passphrase (PBKDF2-HMAC-SHA256, 600,000 iterations). The encryption keys are held by your browser as non-extractable keys, which means their raw bytes cannot be read by any code, including the extension's own.
Your passphrase is never stored and cannot be recovered. If you forget it, the stored values cannot be decrypted by anyone, including us.
The extension can attach a masked file to an open claude.ai or chatgpt.com tab, restore real values inside an answer on those pages, and retrieve a file you have just downloaded from them.
This access is optional and off by default. It is requested only at the moment you use one of those features, applies only to claude.ai, chatgpt.com and chat.openai.com, and can be revoked at any time from the extension's details page in Chrome. If you never grant it, every other feature works unchanged.
When granted, the extension reads text on those pages only to find placeholders it created, and writes to those pages only to insert your masked file or restore your own values. Nothing read from those pages is stored or sent anywhere.
You can turn on a feature that notices when a spreadsheet or document is downloaded from Claude or ChatGPT, so it can offer to restore the masked values in it. This is off by default.