How to anonymize data before using ChatGPT, Claude or Gemini
Anonymizing a prompt means replacing the details that identify real people with neutral placeholders before you send it. The AI still understands the task, because it needs the shape of your request, not the actual names and numbers. Done well, you get an answer that's just as useful, and the real data never leaves your computer.
Why not just turn off training?
Turning off training in ChatGPT, Claude and Gemini's settings is worth doing, but it only controls what the company does with your data after it arrives. Your prompt is still sent, stored with your account, and in some cases kept for safety review. Anonymizing works one step earlier: the sensitive details are never sent at all.
The manual method in 4 steps
1. Find the identifiers
Before pasting, scan the text for anything that points to a real person or account:
- Names (including in email signatures and greetings)
- Email addresses, phone numbers, street addresses
- ID numbers, account numbers, card numbers, IBANs
- Company names, case or project names that could identify a client
- Dates of birth and other dates tied to a person
2. Replace each one with a consistent placeholder
Use a clear label and a number, and use the same placeholder every time the same value appears:
Before: Write a follow-up email to Jane Cohen (jane.cohen@acme.com, 054-381-2297) about invoice #4471 for client ID 3049-7731. Jane prefers calls on Tuesdays.
After: Write a follow-up email to [NAME_1] ([EMAIL_1], [PHONE_1]) about invoice #4471 for client ID [ID_1]. [NAME_1] prefers calls on Tuesdays.
Consistency matters. If "Jane" becomes [NAME_1] in one place and [PERSON] in another, the AI will think they're two different people.
3. Keep the key on your side
Write down which placeholder stands for which value, in a note that stays on your computer. Never paste the key into the same chat.
4. Swap the real details back
When the answer arrives, replace each placeholder with the real value before you use the text. With a long answer, use your editor's find-and-replace so you don't miss one.
Mistakes that undo the work
- Indirect identifiers. "The CFO of a 40-person law firm in Haifa" can identify someone without a single name. Generalize details that aren't needed: "a senior manager at a small firm".
- Files and screenshots. Uploading the original PDF or a screenshot sends everything in it, even if you anonymized the text you typed.
- Forgotten repeats. Names often appear again in signatures, quoted replies and footers at the bottom of a thread.
- Pasting the key. It's surprisingly easy to paste your note with the real values into the chat by mistake.
Is this "anonymization" in the legal sense?
Strictly speaking, replacing details with placeholders while keeping a key is pseudonymization: the data can be re-identified by whoever holds the key. That's the point here, because the key stays with you and the AI company only receives the placeholders. If you work under privacy rules such as GDPR or professional confidentiality, check your organization's policy for what is allowed in AI tools at all (guide for work use).
The automatic way: SafePrompt
The manual method works, but on a busy day it's the step people skip. SafePrompt does the same four steps automatically on ChatGPT, Claude, Gemini, Grok, Copilot and DeepSeek:
- Find: when you press Send, it lists the personal data it found (names, emails, phone numbers, IDs, cards and more).
- Replace: one click on Secure & send swaps each detail for a consistent placeholder like
[[SP_EMAIL_1]]. You can also highlight any word, such as a case name, and click Mask as PII. - Keep the key: the mapping is stored only in your browser tab, and expires after about 30 minutes.
- Swap back: Reveal Original Data puts the real values back into the AI's answer, on your screen only.
Nothing is sent to SafePrompt. It's free to install, with 10 free Secure Sends included.
Quick checklist before you press Send
- Names, emails, phones and addresses replaced
- ID, account and card numbers replaced
- Indirect details generalized (employer, city, job title)
- No original files or screenshots attached
- Your placeholder key kept outside the chat