How nullcipher recognises it
A + and country code with 8–15 digits in total (E.164), a North American (415) 555-2671 / 415-555-2671, or a national number starting with a 0 trunk prefix in space- or dash-separated groups (020 7946 0958, 01 23 45 67 89). A run of digits with no separators, a date, a time or a version number is not a phone.
This is the rule text of the “Phone number” detector in the masking engine, copied from the engine when this page was built. Detectors run in a fixed order and, where two overlap, the earlier one wins.
Example (fake)
+1 415 555 0134nullcipher replaces it with [PHONE_1]. 555-0100 to 555-0199 are the North American numbers NANPA keeps reserved as fictitious, non-working numbers for entertainment and advertising.
Why it matters in an AI chat
A phone number identifies a person, and for many accounts it is also the second factor: sign-in codes and account-recovery messages go to it.
With the rest of a pasted text, a reader can call or text that person with convincing details. A known number is also where a SIM-swap attempt starts: someone persuading the carrier to move the number to their SIM.
nullcipher cannot mask every number. A national number with no + and no leading 0, such as a Danish 12 34 56 78, looks like any other group of digits and goes through unmasked.
If it already leaked
- There is nothing to revoke. Be wary of calls and texts that quote details from the pasted text.
- Ask your mobile carrier whether it offers a PIN or lock on SIM changes and number transfers, and turn it on.
- Where an account allows it, use an authenticator app or a security key for sign-in codes instead of text messages.
Sources
- 555 Line Numbers — NANPA — checked 2026-09-23.
Open the full masking tool to mask a whole log, .env file or e-mail — every type at once — and restore the values in the AI's answer. Or see all 16 secret types and how to delete a chat you already sent.