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Core Nfc Agent Skill

by dpearson2699

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.

8k tokens
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the whole folder, loaded on every use
3
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instructions only
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copies elsewhere
how many repositories repackaged it
960
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on the repository, not the skill itself

Install

one command, takes just this skill from the repository 
npx skills add https://github.com/dpearson2699/swift-ios-skills --skill core-nfc

The instruction itself

20 sections, as written by the author

CoreNFC

Read 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.

Contents

  • Setup
  • NDEF Reader Session
  • Tag Reader Session
  • Writing NDEF Messages
  • NDEF Payload Types
  • Background Tag Reading
  • Common Mistakes
  • Review Checklist
  • References

Setup

Project Configuration

  • Add the Near Field Communication Tag Reading capability in Xcode
  • Add NFCReaderUsageDescription to Info.plist with a user-facing reason string
  • Add the com.apple.developer.nfc.readersession.formats entitlement with the current TAG value; do not add legacy NDEF
  • For ISO 7816 tags, add supported application identifiers to com.apple.developer.nfc.readersession.iso7816.select-identifiers in Info.plist
  • For FeliCa tags, add supported system codes to com.apple.developer.nfc.readersession.felica.systemcodes; do not use wildcard system codes

Device Requirements

NFC 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
}

Key Types

| 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 |

NDEF Reader Session

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
    }
}

Reading with Tag Connection

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()
            }
        }
    }
}

Tag Reader Session

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.

Writing NDEF Messages

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()
            }
        }
    }
}

NDEF Payload Types

Creating Common Payloads

// 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)!
)

Parsing Payload Content

Load Parsing NDEF Payload Content

for the complete type-name-format switch and multi-record handling.

Background Tag Reading

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)
    }
}

Common Mistakes

DON'T: Use stale or missing NFC entitlements

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.

DON'T: Ignore session invalidation errors

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
}

DON'T: Hold a strong reference to a stale session

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()
}

Review Checklist

  • [ ] NFC capability added in Signing & Capabilities
  • [ ] NFCReaderUsageDescription set in Info.plist
  • [ ] com.apple.developer.nfc.readersession.formats entitlement uses TAG, not legacy NDEF
  • [ ] NFCNDEFReaderSession.readingAvailable or NFCTagReaderSession.readingAvailable checked before creating sessions
  • [ ] Session delegate set before calling begin()
  • [ ] Session reference set to nil after invalidation
  • [ ] didInvalidateWithError distinguishes user cancellation from actual errors
  • [ ] NDEF status queried before write operations
  • [ ] Tag capacity checked before writing large messages
  • [ ] ISO 7816 application identifiers listed in Info.plist if using NFCTagReaderSession
  • [ ] FeliCa system codes listed in Info.plist when polling .iso18092
  • [ ] Background tag reading uses a URI NDEF record and universal links or supported system URL schemes
  • [ ] Custom URL schemes, bundle IDs, or arbitrary NDEF content types are not used for background routing
  • [ ] Payment-related AIDs are routed away from NFCTagReaderSession
  • [ ] Only one reader session active at a time

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