 Eiji Kitamura [X](https://twitter.com/agektmr) [GitHub](https://github.com/agektmr) [Mastodon](https://infosec.exchange/@agektmr) [Bluesky](https://bsky.app/profile/agektmr.com)
Published: January 15, 2025, Last updated: April 09, 2026
WebAuthn provides unique capabilities such as interaction with Bluetooth for the
hybrid protocol, communication with passkey providers, and suggesting passkeys
in autofill. However, different clients and authenticators offer varying levels
of support for WebAuthn features. This disparity can lead to a fragmented user
experience, where some users might encounter errors or be unable to utilize
certain authentication options. Providing a way for developers to determine
client capabilities enables them to create more robust authentication flows that
adapt to these variations.
`PublicKeyCredential.getClientCapabilities()` method allows relying parties to
determine which WebAuthn features are supported by the browser. The method
returns a promise that resolves to a list of supported capabilities, allowing
developers to tailor authentication experiences and workflows based on the
client's specific capabilities.
## Compatibility
Browser Support
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[Source](https://developer.mozilla.org/docs/Web/API/PublicKeyCredential/getClientCapabilities_static)
## getClientCapabilities()
The `getClientCapabilities()` is a WebAuthn API that allows relying parties to
determine which capabilities are available. To use the API you need to call
`PublicKeyCredential.getClientCapabilities()`. The returned promise resolves to
an object that contains capabilities, each indicating its availability with
`true` or `false`. If the capability is `undefined`, consider its availability
is not known.
```javascript
if (window.PublicKeyCredential && PublicKeyCredential.getClientCapabilities) {
const capabilities = await PublicKeyCredential.getClientCapabilities();
if (capabilities.conditionalGet === true &&
capabilities.passkeyPlatformAuthenticator === true) {
// The browser supports passkeys and the conditional mediation.
}
}
```
### **conditionalCreate**
The browser can create a credential without a prominent modal UI if the user has
already consented to create one.
### **conditionalGet**
The browser can authenticate by displaying passkeys as part of autofill dialog,
instead of a prominent modal UI. Existing equivalent is
[`PublicKeyCredential.isConditionalMediationAvailable()`](https://developer.mozilla.org/docs/Web/API/PublicKeyCredential/isConditionalMediationAvailable_static).
### **hybridTransport**
The device can use Bluetooth so that the browser can create a credential and
authenticate with it cross-device using the hybrid protocol. This typically
means the browser can display a QR code so that the user can scan it and sign in
with a phone that has a credential on it.
### **passkeyPlatformAuthenticator**
The browser can create a credential and authenticate with it through a user
verifying platform authenticator or another device that supports it through the
hybrid protocol. Equivalent to `hybridTransport ||
userVerifyingPlatformAuthenticator`.
### **relatedOrigins**
The browser can create a credential and authenticate with it that does not match
the RP ID, as long as it's specified in [the related origins
file](https://web.dev/articles/webauthn-related-origin-requests).
### **signalAllAcceptedCredentials**
The browser can [signal available credentials on the server to the passkey
provider](https://developer.chrome.com/docs/identity/webauthn-signal-api#signal-a-list-of-saved-credentials),
so that the passkey provider can keep the passkey list consistent with the
server.
### **signalCurrentUserDetails**
The browser can [signal user information such as username and display name on
the server to the passkey
provider](https://developer.chrome.com/docs/identity/webauthn-signal-api#signal-updated-username-and-display-name),
so that the passkey provider can keep their passkey information consistent with
the server.
### **signalUnknownCredential**
The browser can [signal a deleted credential on the server to the passkey
provider](https://developer.chrome.com/docs/identity/webauthn-signal-api#signal-that-a-credential-does-not-exist),
so that the passkey provider can keep the passkey list consistent with the
server.
### **userVerifyingPlatformAuthenticator**
The browser can create and authenticate with a credential on a platform
authenticator. This does not mean the browser supports the hybrid protocol.
Existing equivalent is
[`PublicKeyCredential.isUserVerifyingPlatformAuthenticatorAvailable()`](https://developer.mozilla.org/docs/Web/API/PublicKeyCredential/isUserVerifyingPlatformAuthenticatorAvailable_static).
### **extensions**
RPs can also determine available extensions with `getClientCapabilities()`.
```javascript
if (capabilities['extension:appid'] === true) {
// appId extension is supported
}
```
The identifier is prefixed with `extension:` followed by an extension name.
Refer to [the WebAuthn Extension Identifiers defined at
IANA](https://www.iana.org/assignments/webauthn/webauthn.xhtml) for extension
names.
## Learn more
To learn more about passkeys, start from [Passwordless login with
passkeys](https://goo.gle/passkeys).