How a Tag Works
The chip has no power source. Holding a phone near it creates a magnetic field that supplies enough energy to wake the chip, and the phone reads its contents. The range is a few centimetres, typically up to about 4 cm, which is why it needs a deliberate tap and cannot be read across a room.
How Much They Hold
Common tag chips are the NTAG family. NTAG213 holds 144 bytes of usable memory, NTAG215 holds 504 and NTAG216 holds 888. A web address needs only a few dozen bytes, so the smallest is enough. The larger ones suit full contact details, but a link keeps the tag useful when those details change.
What Gets Written
Data is stored in the NDEF format, a standard way of describing a record such as a URL or a block of text. A phone that reads a URL record offers to open it. A tag can be locked to read-only so it cannot be overwritten, which is permanent, so write the address correctly and decide first whether it must ever change.
Phone Support
Android phones with NFC read tags when the screen is on and NFC is enabled. iPhones from the XS onwards read tags in the background without an app. Older phones, and some models without NFC, cannot. A tag is therefore a convenience on top of a link rather than a replacement for one.
Frequently asked questions
Does an NFC tag need a battery?
No. It is powered by the phone that reads it, which is why the range is only a few centimetres.
How much data can an NFC tag hold?
It depends on the chip. NTAG213 holds 144 bytes, NTAG215 holds 504 and NTAG216 holds 888. A web address needs very little.
Can an NFC tag be changed after it is written?
Yes, unless it has been locked read-only. A tag that points at an editable page keeps working even if the tag itself is never rewritten.
Keep reading
Related terms
Put this into practice with your own card
Put your details on one card page, share it by link or QR code, and change them whenever they change. The printed code keeps working. No credit card required to start.