Pseudonymize text and files online, reversibly
Paste a text or drop a Word, Excel or CSV file. Each identifying value is replaced by a consistent code such as NAME-001, and the key that reverses it stays in this browser tab. Use the coded version with any AI or share it with a colleague; restore the real values whenever you need them.
Restoring uses the key of this tab: code your text here first, keep this tab open, then come back with the answer.
Adjust
See the key (it stays in this tab)
The key links each code to the real value. It exists only in this tab's memory: close or reload the tab and it is gone.
connect-src 'none' in its security policy) and loads no analytics. Turn Wi-Fi off once the page has loaded: the tool works just the same. The engine is the one inside the Hidden Tokens app.How it works
1 · Code
Paste a text or drop a file. Names, companies, addresses, emails, phone numbers, bank details, ID and case numbers become codes such as NAME-001 or COMPANY-001. Unknown proper nouns are coded too: when in doubt, the engine codes.
2 · Send the codes
Copy the coded text, or download the coded file, and give it to ChatGPT, Claude, Gemini or Copilot. The AI reasons on the codes: it still knows who did what, not who they are.
3 · Restore
Paste the AI's answer in the Restore tab, in the same browser tab. The codes become the real names again, on your screen only.
Pseudonymisation in practice: three properties that matter
The GDPR defines pseudonymisation as processing data so that it can no longer be attributed to a person without additional information, kept separately. In practice, a useful pseudonymisation tool needs three properties, and this one is built around them:
- Consistent. The same value gets the same code everywhere in a run, so analyses, joins and summaries still work:
NAME-004in row 12 isNAME-004in row 840. - Typed. Codes say what they replace (
NAME,COMPANY,EMAIL,IBAN…), so a reader or an AI still knows a person from a bank account. - Reversible, by you only. The key links each code to its value and exists only in this tab. Whoever receives the coded data cannot reverse it.
Pseudonymised data remains personal data for whoever holds the key, so it is not a way out of the GDPR. It is a security measure the regulation explicitly mentions, and a strong one when the key never leaves your hands.
For datasets larger than 1,000 rows, recurring exports or whole folders, the Hidden Tokens app applies the same engine on your computer with one key per folder.
The free tool or the Hidden Tokens app?
This free tool
- One text or one file at a time
- Up to 3,000 words or 1,000 spreadsheet rows
- The key lives in this tab and disappears when you close it
- Word, Excel, CSV and text
The Hidden Tokens app
- Whole folders: the same person keeps the same code in every document
- One key per case file, kept on your computer
- PDF and scanned documents, read on your computer
- Inside Claude Desktop, and in ChatGPT, Gemini and Copilot with the extension
- Industry packs, firm rules and a signed proof of what the AI saw
A word on the word “anonymize”
Strictly speaking, this tool pseudonymizes: each value is replaced by a code that can be reversed with the key. Under the GDPR, pseudonymised data is still personal data for whoever holds the key, which here is you, in this tab. What the AI receives no longer names anyone directly. Clues can remain, such as a job, a town and an age together: the tool warns you when it sees them. Read the result before sending it.
Questions
What is the difference between pseudonymisation and anonymisation?
Pseudonymised data can be re-identified with the key; anonymised data cannot be re-identified by anyone. This tool pseudonymises, which is what you need when you want the real values back in the result.
Does it work on CSV and Excel files?
Yes, up to 1,000 rows per file. The same value gets the same code in every row, so counts and groupings remain correct.
Where is the key stored?
Only in the memory of this browser tab. It is never written to disk or sent anywhere, and it disappears when you close the tab.
Does it make data GDPR-compliant?
No tool makes processing compliant on its own. Pseudonymisation reduces risk and is named in the GDPR as a security measure, but the data stays personal data for you, and indirect clues should be checked before sharing.
Other ways to use the free tool
For whole folders, use the app
Hidden Tokens codes whole case files on your computer with one key, works inside Claude Desktop and in your browser, reads PDFs and scans, and puts the real names back into Word and Excel files.