Presence

Share state between users with Realtime Presence.

Use Realtime Presence to track state between multiple users.

Usage

You can use the Supabase client libraries to track Presence state between users.

How Presence works

Presence lets each connected client publish a small piece of state—called a “presence payload”—to a shared channel. Supabase stores each client’s payload under a unique presence key and keeps a merged view of all connected clients.

When any client subscribes, disconnects, or updates their presence payload, Supabase triggers one of three events:

sync — the full presence state has been updated
join — a new client has started tracking presence
leave — a client has stopped tracking presence

Presence is not designed for high-frequency updates

Presence syncs state through the server and notifies all subscribers on every change. Calling track() rapidly — for example on every mouse move to share cursor positions — will flood the channel and cause performance problems.

For high-frequency or fire-and-forget updates, use Broadcast instead. Presence is best suited for slow-changing state such as online/offline status, active document, or current page.

Sync event behavior

During a sync event, you may receive join and leave events simultaneously, even though no users are joining or leaving. This is expected behavior—Presence reconciles its local state with the server state, which can trigger these events as part of the synchronization process. This reflects state reconciliation, not real user movement.

The complete presence state returned by presenceState() looks like this:

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{
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  "client_key_1": [{ "userId": 1, "typing": false }],
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  "client_key_2": [{ "userId": 2, "typing": true }]
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}

Initialize the client

Get the Project URL and key from the project's Connect dialog.

Changes to API keys

Supabase is deprecating the anon and service_role keys by the end of 2026. Use the publishable (sb_publishable_xxx) and secret (sb_secret_xxx) keys instead. For the reasoning behind the change, see the announcement on GitHub.

In most cases you can get keys from your project's Connect dialog. For every way to retrieve a key, including the CLI and the Management API, refer to Find your keys.

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import {  } from '@supabase/supabase-js'
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const  = 'https://<project>.supabase.co'
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const  = '<sb_publishable_... key>'
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const  = (, )

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void main() {
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  Supabase.initialize(
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    url: 'https://<project>.supabase.co',
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    publishableKey: '<sb_publishable_... key>',
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  );
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  runApp(MyApp());
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}
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final supabase = Supabase.instance.client;

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let supabaseURL = "https://<project>.supabase.co"
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let supabaseKey = "<sb_publishable_... key>"
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let supabase = SupabaseClient(supabaseURL: URL(string: supabaseURL)!, supabaseKey: supabaseKey)
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let realtime = supabase.realtime

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val supabaseUrl = "https://<project>.supabase.co"
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val supabaseKey = "<sb_publishable_... key>"
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val supabase = createSupabaseClient(supabaseUrl, supabaseKey) {
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    install(Realtime)
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}

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from supabase import create_client
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SUPABASE_URL = 'https://<project>.supabase.co'
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SUPABASE_KEY = '<sb_publishable_... key>'
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supabase = create_client(SUPABASE_URL, SUPABASE_KEY)

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var supabase = new Supabase.Client(
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    "https://<project>.supabase.co",
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    "<sb_publishable_... key>"
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);
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await supabase.InitializeAsync();

Sync and track state

Listen to the sync, join, and leave events triggered whenever any client joins or leaves the channel or changes their slice of state:

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const  = .('room_01')
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  .('presence', { : 'sync' }, () => {
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    const  = .()
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    .('sync', )
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  })
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  .('presence', { : 'join' }, ({ ,  }) => {
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    .('join', , )
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  })
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  .('presence', { : 'leave' }, ({ ,  }) => {
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    .('leave', , )
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  })
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  .()

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final supabase = Supabase.instance.client;
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final roomOne = supabase.channel('room_01');
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roomOne.onPresenceSync((_) {
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  final newState = roomOne.presenceState();
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  print('sync: $newState');
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}).onPresenceJoin((payload) {
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  print('join: $payload');
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}).onPresenceLeave((payload) {
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  print('leave: $payload');
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}).subscribe();

Listen to the presence change stream, emitting a new PresenceAction whenever someone joins or leaves:

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let roomOne = await supabase.channel("room_01")
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let presenceStream = await roomOne.presenceChange()
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await roomOne.subscribe()
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for await presence in presenceStream {
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  print(presence.join) // You can also use presence.decodeJoins(as: MyType.self)
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  print(presence.leaves) // You can also use presence.decodeLeaves(as: MyType.self)
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}

Listen to the presence change flow, emitting new a new PresenceAction whenever someone joins or leaves:

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val roomOne = supabase.channel("room_01")
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val presenceFlow: Flow<PresenceAction> = roomOne.presenceChangeFlow()
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presenceFlow
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    .onEach {
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        println(it.joins) //You can also use it.decodeJoinsAs<YourType>()
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        println(it.leaves) //You can also use it.decodeLeavesAs<YourType>()
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    }
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    .launchIn(yourCoroutineScope) //You can also use .collect { } here
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roomOne.subscribe()

Listen to the sync, join, and leave events triggered whenever any client joins or leaves the channel or changes their slice of state:

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room_one = supabase.channel('room_01')
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room_one
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  .on_presence_sync(lambda: print('sync', room_one.presenceState()))
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  .on_presence_join(lambda key, curr_presences, joined_presences: print('join', key, curr_presences, joined_presences))
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  .on_presence_leave(lambda key, curr_presences, left_presences: print('leave', key, curr_presences, left_presences))
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  .subscribe()

Listen to the Sync, Join, and Leave events triggered whenever any client joins or leaves the channel or changes their slice of state:

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class UserStatus : BasePresence
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{
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    [JsonProperty("user")]
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    public string User { get; set; }
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    [JsonProperty("online_at")]
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    public string OnlineAt { get; set; }
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}
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var roomOne = supabase.Realtime.Channel("room_01");
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var presence = roomOne.Register<UserStatus>(Guid.NewGuid().ToString());
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presence.AddPresenceEventHandler(EventType.Sync, (sender, type) =>
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{
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    Console.WriteLine($"sync: {presence.CurrentState}");
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});
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presence.AddPresenceEventHandler(EventType.Join, (sender, type) => Console.WriteLine("join"));
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presence.AddPresenceEventHandler(EventType.Leave, (sender, type) => Console.WriteLine("leave"));
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await roomOne.Subscribe();

Sending state

You can send state to all subscribers using track():

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const  = .('room_01')
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const  = {
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  : 'user-1',
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  : new ().(),
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}
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.(async () => {
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  if ( !== 'SUBSCRIBED') { return }
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  const  = await .()
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  .()
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})

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final roomOne = supabase.channel('room_01');
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final userStatus = {
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  'user': 'user-1',
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  'online_at': DateTime.now().toIso8601String(),
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};
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roomOne.subscribe((status, error) async {
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  if (status != RealtimeSubscribeStatus.subscribed) return;
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  final presenceTrackStatus = await roomOne.track(userStatus);
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  print(presenceTrackStatus);
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});

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let roomOne = await supabase.channel("room_01")
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// Using a custom type
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let userStatus = UserStatus(
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    user: "user-1",
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    onlineAt: Date().timeIntervalSince1970
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)
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await roomOne.subscribe()
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try await roomOne.track(userStatus)
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// Or using a raw JSONObject.
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await roomOne.track(
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  [
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    "user": .string("user-1"),
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    "onlineAt": .double(Date().timeIntervalSince1970)
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  ]
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)

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val roomOne = supabase.channel("room_01")
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val userStatus = UserStatus( //Your custom class
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    user = "user-1",
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    onlineAt = Clock.System.now().toEpochMilliseconds()
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)
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roomOne.subscribe(blockUntilSubscribed = true) //You can also use the roomOne.status flow instead, but this parameter will block the coroutine until the status is joined.
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roomOne.track(userStatus)

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room_one = supabase.channel('room_01')
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user_status = {
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  "user": 'user-1',
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  "online_at": datetime.datetime.now().isoformat(),
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}
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def on_subscribe(status, err):
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  if status != RealtimeSubscribeStates.SUBSCRIBED:
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    return
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  room_one.track(user_status)
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room_one.subscribe(on_subscribe)

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var roomOne = supabase.Realtime.Channel("room_01");
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var presence = roomOne.Register<UserStatus>(Guid.NewGuid().ToString());
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await roomOne.Subscribe();
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await presence.Track(new UserStatus
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{
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    User = "user-1",
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    OnlineAt = DateTime.UtcNow.ToString("o")
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});

A client will receive state from any other client that is subscribed to the same topic (in this case room_01). It will also automatically trigger its own sync and join event handlers.

Stop tracking

You can stop tracking presence using the untrack() method. This will trigger the sync and leave event handlers.

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const  = async () => {
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  const  = await .()
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  .()
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}
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()

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final roomOne = supabase.channel('room_01');
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untrackPresence() async {
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  final presenceUntrackStatus = await roomOne.untrack();
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  print(presenceUntrackStatus);
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}
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untrackPresence();

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await roomOne.untrack()

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suspend fun untrackPresence() {
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	roomOne.untrack()
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}
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untrackPresence()

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room_one.untrack()

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await presence.Untrack();

Presence options

You can pass configuration options while initializing the Supabase Client.

Presence key

By default, Presence will generate a unique UUIDv1 key on the server to track a client channel's state. If you prefer, you can provide a custom key when creating the channel. This key should be unique among clients.

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import {  } from '@supabase/supabase-js'
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const  = ('SUPABASE_URL', 'SUPABASE_PUBLISHABLE_KEY')
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const  = .('test', {
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  : {
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    : {
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      : 'userId-123',
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    },
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  },
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})

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final channelC = supabase.channel(
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  'test',
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  opts: const RealtimeChannelConfig(key: 'userId-123'),
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);

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let channelC = await supabase.channel("test") {
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  $0.presence.key = "userId-123"
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}

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val channelC = supabase.channel("test") {
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    presence {
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        key = "userId-123"
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    }
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}

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channel_c = supabase.channel('test', {
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  "config": {
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    "presence": {
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      "key": 'userId-123',
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    },
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  },
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})

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var channelC = supabase.Realtime.Channel("test");
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var presence = channelC.Register<UserStatus>("userId-123");

The Realtime Avatar Stack in the Supabase Library is a Presence-based web component you can install with a single command.

Presence

Usage

How Presence works

Initialize the client

Sync and track state

Sending state

Stop tracking

Presence options

Presence key

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Usage

How Presence works

Initialize the client

Sync and track state

Sending state

Stop tracking

Presence options

Presence key

Related resources

Is this helpful?

AI tools