> For the complete documentation index, see [llms.txt](https://webauthn-doc.spomky-labs.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://webauthn-doc.spomky-labs.com/webauthn-in-a-nutshell/authenticators.md).
# Authenticators
What is an authenticator?
An Authenticator is a cryptographic entity used to generate a public key credential and registered by a Relying Party (i.e. an application). This public key is used to authenticate by potentially verifying a user in the form of an authentication assertion and other data.
Authenticators may have additional features such as PIN code or biometric sensors (fingerprint, facial recognition…) that offer user verification.
## Roaming Authenticators
The roaming authenticator may have different forms. The most common form is a USB device the user plugs into their computer. It can be a paired Bluetooth device or a card with NFC capabilities.
Authenticators of this class are removable from, and can "roam" among, client devices.
## Platform Authenticators
A platform authenticator is usually not removable from the client device. For example an Android smartphone or a Windows 10 computer with the associated security chips can act as an authenticator.
### Passkey
Passkey Logo
Passkeys are virtual authenticators that have extended capabilities and in particular:
* Synchronized and stored in an integrated password manager (e.g., iCloud Keychain, Google Password Manager).
* Simple and integrated use, no need for an external device.
* Seamless synchronization across different user devices.
* Backed up automatically through the associated cloud service, allowing easy recovery if a device is lost or replaced.
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