When a web site or app using RTCPeerConnection receives a new ICE candidate from the remote peer over its signaling channel, it delivers the newly-received candidate to the browser's ICE agent by calling RTCPeerConnection.addIceCandidate(). This adds this new remote candidate to the RTCPeerConnection's remote description, which describes the state of the remote end of the connection.

If the value of the specified object's candidate is an empty string (""), it signals that all remote candidates have been delivered (end-of-candidates).

During negotiation, your app will likely receive many candidates which you'll deliver to the ICE agent in this way, allowing it to build up a list of potential connection methods. This is covered in more detail in the articles WebRTC connectivity and Signaling and video calling.


aPromise = pc.addIceCandidate(candidate);

addIceCandidate(candidate, successCallback, failureCallback);  


An object conforming to the RTCIceCandidateInit dictionary; the contents of the object should be constructed from a message received over the signaling channel, describing a newly received ICE candidate that's ready to be delivered to the local ICE agent.

Deprecated parameters

In older code and documentation, you may see a callback-based version of this function. This has been deprecated and its use is strongly discouraged. You should update any existing code to use the Promise-based version of addIceCandidate() instead. The parameters for this form of addIceCandidate() are described below, to aid in updating existing code.

A function to be called when the ICE candidate has been successfully added. This function receives no input parameters and doesn't return a value.
A function to be called if attempting to add the ICE candidate fails. Receives as input a DOMException object describing why failure occurred.

Return value

A Promise which is fulfilled when the candidate has been successfully added to the remote peer's description by the ICE agent. The promise does not receive any input parameters.


When an error occurs while attempting to add the ICE candidate, the Promise returned by this method is rejected, returning one of the errors below as the name attribute in the specified DOMException object passed to the rejection handler.

The specified candidate's sdpMid and sdpMLineIndex are both null.
The RTCPeerConnection currently has no remote peer established (remoteDescription is null).
This can happen for a number of reasons:
  • The value specified for sdpMid is non-null and doesn't match the media description ID of any media description included within the remoteDescription.
  • The specified value of sdpMLineIndex is greater than or equal to the number of media descriptions included in the remote description.
  • The specified ufrag doesn't match the ufrag field in any of the remote descriptions being considered.
  • One or more of the values in the candidate string are invalid or could not be parsed.
  • Attempting to add the candidate fails for any reason. 


This code snippet shows how to signal ICE candidates across an arbitrary signaling channel.

// This example assumes that the other peer is using a signaling channel as follows:
// pc.onicecandidate = event => {
//   if (event.candidate) {
//     signalingChannel.send(JSON.stringify({ice: event.candidate})); // "ice" is arbitrary
//   } else {
//     // All ICE candidates have been sent
//   }
// }

signalingChannel.onmessage = receivedString => {
  const message = JSON.parse(receivedString);
  if (message.ice) {
    // A typical value of ice here might look something like this:
    // {candidate: "candidate:0 1 UDP 2122154243 53421 typ host", sdpMid: "0", ...}
    // Pass the whole thing to addIceCandidate:

    pc.addIceCandidate(message.ice).catch(e => {
      console.log("Failure during addIceCandidate(): " + e.name);
  } else {
    // handle other things you might be signaling, like sdp

The last candidate to be signaled this way by the remote peer will be a special candidate denoting end-of-candidates. Out of interest, end-of-candidates may be manually indicated as follows:



Specification Status Comment
WebRTC 1.0: Real-time Communication Between Browsers
The definition of 'RTCPeerConnection.addIceCandidate()' in that specification.
Candidate Recommendation Initial specification.
WebRTC 1.0: Real-time Communication Between Browsers
The definition of 'RTCPeerConnection.addIceCandidate()' in that specification.
Candidate Recommendation Initial specification.

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support


50 — 562

1522 ?


37 — 43

FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support


50 — 562


50 — 562



37 — 43



5.0 — 6.02

1. Promise based version and unprefixed.

2. Promise based version.

See also

Document Tags and Contributors

Contributors to this page: Jib, boldt, Sheppy, fscholz, jpmedley, abbycar, cauburtin, rolfedh
Last updated by: Jib,