How NFC Actually Works — From Antenna Coupling to NDEF Records

NFC works by inductive coupling between two loop antennas at 13.56 MHz, with the data on the tag wrapped in a portable format called NDEF. That's the whole story. Every tap-to-pay terminal, smart-home sticker, vCard tag, and event wristband is a variation on those two ideas.

Once you understand the radio link and the record format, the rest of the NFC ecosystem stops feeling like magic. The sections below walk through both, then show where you'll see them in everyday life.

The radio link — 13.56 MHz and a tiny magnetic field

NFC operates at 13.56 MHz in the unlicensed ISM band, at data rates of 106, 212, 424, or 848 kbit/s. The link is inductive: the reader's antenna and the tag's antenna form an air-core transformer. The reader generates an alternating magnetic field, the tag's coil picks up enough current to power its chip, and the tag replies by modulating the field the reader is already producing.

Almost no energy is radiated as a true radio wave — that's why range is roughly 4 cm in practice. The short range is a feature, not a limitation. Your phone won't accidentally read the tag in someone else's pocket.

Type A vs Type B (ISO/IEC 14443)

NFC inherits its physical and link layers from ISO/IEC 14443, the proximity-card standard. Type A uses amplitude-shift keying with Modified Miller coding from reader to tag, and Manchester back. That's what most consumer NDEF stickers speak — the NTAG213, NTAG215, and NTAG216 family. Type B uses ASK with NRZ-L going out and BPSK coming back, and shows up on government IDs and some payment cards. The reader detects which type a tag uses during the anti-collision handshake, so you almost never have to think about it.

What NDEF actually is

Once the radio link is up, the bytes flowing across it have to mean something. That's where NDEF — the NFC Data Exchange Format comes in. An NDEF message is a sequence of NDEF records, and each record has four parts:

• A TNF (Type Name Format) that names the namespace of the type field — Well-Known, MIME Media, Absolute URI, External, Empty, or Unknown
• A Type identifier within that namespace
• An optional ID
• A payload — the actual bytes

No file system, no directory — just a flat list of records. The first record's TNF is what tells the reader how to interpret the whole message.

The records you'll actually meet

• Text (T) — UTF-8 text plus a language tag. Free-form descriptions.
• URI (U) — a URI with a one-byte abbreviation prefix for common schemes (http://, https://, tel:, mailto:, sms:). The most common record on consumer tags.
• Smart Poster (Sp) — a URI plus optional title, action, type, size, and icon records bundled together.
• Signature — a cryptographic signature over the rest of the message.

Where you'll see NDEF in the wild

The same record format quietly powers most of the NFC interactions you already use:

• Background tag reading on iPhone XS and later — tap an unlocked phone against a tag with a URI record and Safari opens the link without you launching anything.
• Wi-Fi handover tags — a special record format hands an SSID and password to the OS so guests join with one tap.
• vCard stickers and NFC business cards — a MIME-type record carrying a vCard saves a contact in one motion.
• Smart-home automation — iOS Shortcuts, Home Assistant, and HomeKit each support NFC tag triggers via standard NDEF.

Cross-platform portability is the real win. Android's NdefRecord and iOS's NFCNDEFPayload expose the identical TNF, type, identifier, and payload structure, so a tag written from one platform reads cleanly on the other. For more on individual record types and tag families, see more NFC explainers.

Reading and writing tags from your phone

The phone OS gives you a lot for free. Apple's Core NFC exposes NFCNDEFReaderSession for reads and the writeNDEF method on NFCNDEFTag for writes. On Android, NdefRecord ships static factories — createUri(), createTextRecord(), createMime() — that build well-formed records without you hand-encoding bytes.

That covers standard NDEF. For the layer below — raw memory dumps, lock-byte inspection, batch writes, custom APDU commands, or telling whether a chip is an NTAG215 or a MIFARE Ultralight before you write to it — you need a tool that exposes the protocol layer. NFCore's Tag Inspector and Memory Dump views show the chip type, UID, lock state, and page-by-page contents in hex and ASCII, so you can see what's actually on the tag before you change it.

Frequently asked questions

How far does NFC actually reach?

About 4 cm in practice. The signal is a near-field magnetic coupling, not a radiated radio wave, so signal strength drops off sharply with distance. That short range is a feature — it's why an accidental tap on the wrong tag is unlikely.

Is NFC the same thing as RFID?

NFC is a specific subset of RFID that operates at 13.56 MHz and follows the ISO/IEC 14443 and FeliCa standards. Most general-purpose RFID runs at different frequencies (125 kHz, UHF) and isn't readable by a phone. If you can tap a tag with an iPhone or Android, it's NFC.

Does my phone need an app to read an NFC tag?

Not for standard NDEF tags carrying a URL. iPhone XS and newer, plus essentially every modern Android, will read a URI record in the background and offer to open the link. For raw memory dumps, NDEF writing, or non-URL records, you need an app like NFCore.

Why does my old NFC tag say "tag not supported"?

Usually one of three things: the tag is locked and your app is trying to write, the tag is a 125 kHz RFID format your phone can't reach, or the NDEF message on it is malformed. Use NFCore's Tag Inspector to check the chip type and lock state before writing.

Where to go next

NFC is two ideas: a short-range magnetic link at 13.56 MHz, and a record format called NDEF that any phone can read. Once you've seen one record, you've seen all of them — what changes is the payload. To watch a real NDEF message come up live, tap a tag in the NFCore guides walkthrough.