Advanced Usage


Sometimes, you may not want all events to be published to all clients. For example, a client that cares about receiving the latest updates in their social network probably doesn’t care about receiving the latest statistics about how many users are online across the entire site, and vice versa. When publishing an event, you can select which channel to direct the event to. If you do, only clients that are checking that particular channel will receive the event. For example, this event will be sent to the “” channel:

sse.publish({"user": "alice", "status": "Life is good!"}, channel="")

And this event will be sent to the “analytics” channel:

sse.publish({"active_users": 100}, channel="analytics")

Channel names can be any string you want, and are created dynamically as soon as they are referenced. The default channel name that Flask-SSE uses is “sse”. For more information, see the documentation for the Redis pubsub system.

To subscribe to a channel, the client only needs to provide a channel query parameter when connecting to the event stream. For example, if your event stream is at /stream, you can connect to the “” channel by using the URL /stream? You can also use Flask’s url_for() function to generate this query parameter, like so:

url_for("", channel="")

By default, all channels are publicly accessible to all users. However, see the next section to change that.

Access Control

Since Flask-SSE is implemented as a blueprint, you can attach a before_request() handler to implement access control. For example:

def check_access():
    if request.args.get("channel") == "analytics" and not g.user.is_admin():

app.register_blueprint(sse, url_prefix='/sse')


When defining a before_request() handler, the blueprint must be registered after the handler is defined! Otherwise, the handler will have no effect.