Connectivity - USB, NFC & Accessory

Transports

Core discovers YubiKeys over two transports:

USB - covers both Lightning/MFi accessory connections on iOS (YKFAccessoryConnection) and USB-C "smart card" connections on iOS 16+ (YKFSmartCardConnection), plus USB OTG on Android. The JS Transport type only reports 'usb' for all of these - there's no way from JS to tell whether a given USB device is connected via Lightning-accessory or USB-C-smart-card on iOS.
NFC - tap-to-connect on NFC-capable devices, on both platforms.

type Transport = 'usb' | 'nfc';

There is no hasMFiSupport() check, no getMFiDevices(), and no separate "MFi connected/disconnected" event stream. Everything goes through the same Core.addYubiKeyListener event stream regardless of transport.

Starting discovery

import { Core } from '@doko/react-native-yubikit';

// USB (covers Lightning accessory + USB-C smart card on iOS, USB OTG on Android)
Core.startUsbDiscovery({ handlePermissions: true });

// NFC
Core.startNfcDiscovery({
  timeout: 20000,
  disableNfcDiscoverySound: false,
});

Core.stopUsbDiscovery();
Core.stopNfcDiscovery();

One real platform difference worth knowing: on iOS, the native code for startUsbDiscovery / startNfcDiscovery doesn't currently read any fields off the config object you pass in - options like handlePermissions, timeout, disableNfcDiscoverySound are honored on Android but silently ignored on iOS. Don't rely on iOS respecting a custom timeout or discovery-sound setting.

Listening for devices

import { Core } from '@doko/react-native-yubikit';
import type { YubiKeyEvent } from '@doko/react-native-yubikit';

const subscription = Core.addYubiKeyListener((event: YubiKeyEvent) => {
  if (event.type === 'attached') {
    // event.device: YubiKeyDevice - has a `handle` you pass to every other module
  } else if (event.type === 'detached') {
    // event.handle: string
  } else if (event.type === 'error') {
    // event.error: string - e.g. a failed NFC/smart-card connection attempt
  }
});

// later
subscription.remove();

iOS: Lightning vs USB-C smart card

Lightning (5Ci, MFi accessory): works via YKFAccessoryConnection on iOS versions supported by YubiKit iOS SDK 4.7.0 - no special iOS-version gate beyond what the SDK itself requires.
USB-C smart card (5C and similar over the native USB-C port): requires iOS 16+, gated with if (@available(iOS 16.0, *)) in the native connection code (YKFSmartCardConnection).

If you need to distinguish these in your UI, you can't do it from the JS Transport/device data alone - both surface as 'usb'.

Android: USB OTG

USB devices are discovered through the standard Android USB host APIs. Permission is requested at runtime by the YubiKit Android SDK itself when you call Core.startUsbDiscovery({ handlePermissions: true }) - there's no manifest permission for this (see Installation for why USB_PERMISSION isn't a real Android permission string).

iOS setup you still have to do yourself, per transport

Neither platform's transport support is fully "automatic." On iOS, depending on which transports you need:

Lightning (5Ci): add com.yubico.ylp under UISupportedExternalAccessoryProtocols in Info.plist.
USB-C smart card (iOS 16+): add the com.apple.security.smartcard entitlement.
NFC: add NFCReaderUsageDescription, the NFC reader-session capability, and the AID list (com.apple.developer.nfc.readersession.iso7816.select-identifiers).

See Installation for the exact snippets. None of this is done by the library's podspec, and the library's own example app doesn't configure any of it either - its Info.plist has no NFC keys and its entitlements file is empty. On Android, the NFC permission is already merged in via the library's manifest, so no extra manifest work is required there.

Requirements for the device-compatibility table
Installation for the exact Info.plist / Podfile steps
Usage Examples for a full discover-then-operate flow