Since WLED 0.10.2, a WebSocket server is enabled by default and can be used to access a subset of the JSON API.

The server is available at the /ws endpoint, you can access it like ws://[WLED-IP]/ws.

You may send any JSON state update to the socket. On change of the lighting state, the server will send a JSON object containing the state and info objects (this is equivalent to HTTP GET /json/si) to all connected clients. This object will also be sent to a client upon connecting.

You can also request a live stream of the LED values (e.g. the "Peek" feature of WLED-UI) by sending {"lv":true} to the websocket. The returned format is the same as for /json/live. Only one client can receive this at a time, if a new client requests it the stream will stop for the previous client (but the websocket will stay connected).

There can be a maximum of 4 clients connected at a time. If a fifth client connects, a different client will be disconnected. On ESP8266, it is recommended to have no more than 2 clients connected simultaneously.