How to Write an NFC Tag with Your Phone — Step-by-Step

Writing an NFC tag comes down to saving an NDEF message to it with a phone app — pick a record type (a link, some text, a contact, or Wi-Fi credentials), hold your phone to the tag, and confirm. It works on Android and on any iPhone 7 or newer running iOS 13 or later, as long as the tag is writable and has room for what you're storing.

What writing an NFC tag actually means

Every consumer NFC tag stores its data in NDEF, the wrapper format defined by the NFC Forum. An NDEF message holds one or more records, and each record carries a type, an optional ID, and a payload. That shared standard is exactly why a tag you write on an Android phone reads back cleanly on an iPhone — both speak the same format.

The record types you'll actually reach for are a short list. A URI record holds a link. A Text record holds plain text with a language code. A MIME record carries a vCard contact (text/vcard) or a set of Wi-Fi credentials (application/vnd.wfa.wsc). A Smart Poster bundles a URL with a title and an action hint. And an external-type record holds app-specific data for a particular app. Android's NdefRecord helpers build these for you, and createUri() even abbreviates common prefixes like https://www. into a single identifier byte to save space on small tags.

Picking the right record matters, because it decides what the phone does on a tap. A URI record opens a link in the browser. A vCard offers to save a contact. A Wi-Fi record offers to join the network. Match the record type to the behavior you want, and the reading phone handles the rest with no extra app required.

Step-by-step

1. Get a writable tag and an app. The common consumer chips are NTAG213, NTAG215, and NTAG216. Any NFC writer app will do — NFCore, or a general-purpose tool like NFC Tools.
2. Choose the record type and enter your data. A link, a phone number, a full contact card, or your Wi-Fi network name and password.
3. Write it. Tap Write in the app, then hold the top edge of an iPhone — or the back of most Android phones — flat against the tag until the app confirms. Keep it still: NFC range is only about 4 cm.
4. Read it back to verify. Scan the tag once to confirm the payload actually landed.

On Android, the write path uses the Ndef tech class, and a brand-new blank tag sometimes needs to be NDEF-formatted first — something apps handle for you. On iPhone, Core NFC checks whether the tag is writable before it sends anything, then writes the message in a single tap.

Common problems and fixes

"Tag is read-only." Someone locked it. A permanently locked tag has its lock bytes set and can never be rewritten — there is no undo. Reach for a fresh tag instead.

"Not enough memory." Your payload is bigger than the chip. An NTAG213 holds 144 bytes, an NTAG215 holds 504, and an NTAG216 holds 888. A short URL fits anywhere; a vCard with a photo can overflow the smaller chips. Shorten the URL or step up a chip — our NTAG comparison walks through the trade-offs.

"Tag isn't formatted." A blank tag straight off the roll sometimes carries no NDEF structure yet. Most writer apps format it for you on the first write, so just try writing again; if the app exposes a separate Format option, run that first.

Nothing happens at all. The tag might be a 125 kHz card, which isn't NFC even though it looks identical. Phones only read and write 13.56 MHz NFC tags, so a low-frequency fob or an old hotel key won't respond no matter what you do.

iPhone won't write. Writing needs iOS 13 or later on an iPhone 7 or newer. A few older models can read tags but can't write them, so check your hardware before you blame the tag.

Doing this on NFCore

NFCore's Write Data flow walks through exactly these steps: choose a record type, enter the data, and hold the phone to the tag. There are templates for URLs, text, vCards, and Wi-Fi, so you don't have to assemble the record by hand. When you're certain a tag is final, you can lock it to read-only — but treat that as a one-way decision, because locking can't be reversed. Everything happens on your phone; NFCore doesn't track you or upload your data anywhere. Grab it on the App Store or Google Play and write your first tag in under a minute.