dpearson2699/core-nfc
Read and write NFC tags using CoreNFC. Use when scanning NDEF tags, reading ISO7816/ISO15693/FeliCa/MIFARE tags, writing NDEF messages, handling NFC session lifecycle, configuring NFC entitlements, or implementing background tag reading in iOS apps.
npx skills add https://github.com/dpearson2699/swift-ios-skills --skill core-nfcRead and write NFC tags on iPhone using the CoreNFC framework. Covers NDEF
reader sessions, tag reader sessions, NDEF message construction, entitlements,
and background tag reading.
NFCReaderUsageDescription to Info.plist with a user-facing reason stringcom.apple.developer.nfc.readersession.formats entitlement with the current TAG value; do not add legacy NDEFcom.apple.developer.nfc.readersession.iso7816.select-identifiers in Info.plistcom.apple.developer.nfc.readersession.felica.systemcodes; do not use wildcard system codesNFC reading requires iPhone 7 or later. Always check for reader session
availability before creating NFC UI or sessions. Use the concrete reader
session type you are about to create.
import CoreNFC
guard NFCNDEFReaderSession.readingAvailable else {
// Device does not support NFC or feature is restricted
showUnsupportedMessage()
return
}
| Type | Role |
|---|---|
| NFCNDEFReaderSession | Scans for NDEF-formatted tags |
| NFCTagReaderSession | Scans for ISO7816, ISO15693, FeliCa, MIFARE tags |
| NFCNDEFMessage | Collection of NDEF payload records |
| NFCNDEFPayload | Single record within an NDEF message |
| NFCNDEFTag | Protocol for interacting with an NDEF-capable tag |
Use NFCNDEFReaderSession to read NDEF-formatted data from tags. This is the
simplest path for reading standard tag content like URLs, text, and MIME data.
import CoreNFC
final class NDEFReader: NSObject, NFCNDEFReaderSessionDelegate {
private var session: NFCNDEFReaderSession?
func beginScanning() {
guard NFCNDEFReaderSession.readingAvailable else { return }
session = NFCNDEFReaderSession(
delegate: self,
queue: nil,
invalidateAfterFirstRead: false
)
session?.alertMessage = "Hold your iPhone near an NFC tag."
session?.begin()
}
// MARK: - NFCNDEFReaderSessionDelegate
func readerSessionDidBecomeActive(_ session: NFCNDEFReaderSession) {
// Session is scanning
}
func readerSession(
_ session: NFCNDEFReaderSession,
didDetectNDEFs messages: [NFCNDEFMessage]
) {
for message in messages {
for record in message.records {
processRecord(record)
}
}
}
func readerSession(
_ session: NFCNDEFReaderSession,
didInvalidateWithError error: Error
) {
let nfcError = error as? NFCReaderError
if nfcError?.code != .readerSessionInvalidationErrorFirstNDEFTagRead,
nfcError?.code != .readerSessionInvalidationErrorUserCanceled {
print("Session invalidated: \(error.localizedDescription)")
}
self.session = nil
}
}
For read-write operations, use the tag-detection delegate method to connect
to individual tags:
func readerSession(
_ session: NFCNDEFReaderSession,
didDetect tags: [any NFCNDEFTag]
) {
guard let tag = tags.first else {
session.restartPolling()
return
}
session.connect(to: tag) { error in
if let error {
session.invalidate(errorMessage: "Connection failed: \(error)")
return
}
tag.queryNDEFStatus { status, capacity, error in
guard error == nil else {
session.invalidate(errorMessage: "Query failed.")
return
}
switch status {
case .notSupported:
session.invalidate(errorMessage: "Tag is not NDEF compliant.")
case .readOnly:
tag.readNDEF { message, error in
if let message {
self.processMessage(message)
}
session.invalidate()
}
case .readWrite:
tag.readNDEF { message, error in
if let message {
self.processMessage(message)
}
session.alertMessage = "Tag read successfully."
session.invalidate()
}
@unknown default:
session.invalidate()
}
}
}
}
Use NFCTagReaderSession when you need direct access to the native tag
protocol (ISO 7816, ISO 15693, FeliCa, or MIFARE).
| Polling option | Tags |
|---|---|
| .iso14443 | ISO 7816-compatible and MIFARE |
| .iso15693 | ISO 15693 |
| .iso18092 | FeliCa |
Do not use this session for payment-related AIDs. Load
nfc-patterns.md for protocol-specific connection,
APDU, command, and response handling.
Write NDEF data to a connected tag. Always check readWrite status first.
func writeToTag(
tag: any NFCNDEFTag,
session: NFCNDEFReaderSession,
url: URL
) {
tag.queryNDEFStatus { status, capacity, error in
guard status == .readWrite else {
session.invalidate(errorMessage: "Tag is read-only.")
return
}
guard let payload = NFCNDEFPayload.wellKnownTypeURIPayload(
url: url
) else {
session.invalidate(errorMessage: "Invalid URL.")
return
}
let message = NFCNDEFMessage(records: [payload])
tag.writeNDEF(message) { error in
if let error {
session.invalidate(
errorMessage: "Write failed: \(error.localizedDescription)"
)
} else {
session.alertMessage = "Tag written successfully."
session.invalidate()
}
}
}
}
// URL payload
let urlPayload = NFCNDEFPayload.wellKnownTypeURIPayload(
url: URL(string: "https://example.com")!
)
// Text payload
let textPayload = NFCNDEFPayload.wellKnownTypeTextPayload(
string: "Hello NFC",
locale: Locale(identifier: "en")
)
// Custom payload
let customPayload = NFCNDEFPayload(
format: .nfcExternal,
type: "com.example:mytype".data(using: .utf8)!,
identifier: Data(),
payload: "custom-data".data(using: .utf8)!
)
Load Parsing NDEF Payload Content
for the complete type-name-format switch and multi-record handling.
On iPhone XS and later, iOS can read NFC tags in the background without
opening your app. The NDEF message must contain a URI record
(typeNameFormat == .nfcWellKnown, type U). If there are multiple URI
records, the system uses the first one.
For app-specific routing, write a universal link to the tag and configure the
Associated Domains capability for that domain. Background tag reading also
supports specific system URL schemes such as web, email, SMS, telephone,
FaceTime, Maps, and HomeKit setup. It does not support custom URL schemes, and
the system does not route by bundle ID or arbitrary NDEF content type.
When a user taps a compatible tag, iOS displays a notification that opens
your app. Handle the tag data via NSUserActivity:
func scene(
_ scene: UIScene,
continue userActivity: NSUserActivity
) {
guard userActivity.activityType ==
NSUserActivityTypeBrowsingWeb else { return }
let message = userActivity.ndefMessagePayload
guard message.records.first?.typeNameFormat != .empty else { return }
for record in message.records {
processRecord(record)
}
}
Without the com.apple.developer.nfc.readersession.formats entitlement,
reader sessions cannot access NFC hardware. Use the current TAG value for
Core NFC reader sessions; do not copy older examples that add NDEF.
The session invalidates for multiple reasons. Distinguishing user cancellation
from real errors prevents false error alerts.
// WRONG -- shows error when user cancels
func readerSession(
_ session: NFCNDEFReaderSession,
didInvalidateWithError error: Error
) {
showAlert("NFC Error: \(error.localizedDescription)")
}
// CORRECT -- filter expected invalidation reasons
func readerSession(
_ session: NFCNDEFReaderSession,
didInvalidateWithError error: Error
) {
let nfcError = error as? NFCReaderError
switch nfcError?.code {
case .readerSessionInvalidationErrorUserCanceled,
.readerSessionInvalidationErrorFirstNDEFTagRead:
break // Normal termination
default:
showAlert("NFC Error: \(error.localizedDescription)")
}
self.session = nil
}
Once a session is invalidated, it cannot be restarted. Nil out your reference
and create a new session for the next scan.
// WRONG -- reusing invalidated session
func scanAgain() {
session?.begin() // Does nothing, session is dead
}
// CORRECT -- create a new session
func scanAgain() {
session = NFCNDEFReaderSession(
delegate: self, queue: nil, invalidateAfterFirstRead: false
)
session?.begin()
}
NFCReaderUsageDescription set in Info.plistcom.apple.developer.nfc.readersession.formats entitlement uses TAG, not legacy NDEFNFCNDEFReaderSession.readingAvailable or NFCTagReaderSession.readingAvailable checked before creating sessionsbegin()didInvalidateWithError distinguishes user cancellation from actual errorsNFCTagReaderSession.iso18092NFCTagReaderSessionTake dpearson2699/core-nfc from the repository into ~/.claude/skills for personal
use, or into .claude/skills inside a project.
The agent identifies a skill by the name field in its header. Two skills with the
same name cannot sit side by side — one of them will be ignored.