How to write a blank NFC card

1. Turn NFC on in your phone settings.
2. Install a free NFC writing app: NFC Tools or NXP TagWriter on Android, NFC Tools on iPhone XS or newer.
3. Open the app and tap Write.
4. Add a record: a website link, a text, or a contact.
5. Tap Write again and hold the card flat on the back of the phone until the app confirms.

You can rewrite the card as many times as you like, unless you choose Lock in the app. Locking is permanent.

Tip: do the first write on an Android phone. iPhones mainly read NFC, and first-time writing on an iPhone often fails.

The full guide with screenshots is at blanknfc.com.