ESP8266 - WebSocket

In this tutorial, we will learn what WebSocket is, why we need to use it to smoothly control ESP8266, and how to use WebSocket with ESP8266. In a practical example, we will learn how to create a chat application between the web browser and ESP8266, allowing you to:

ESP8266 NodeMCU websocket

Hardware Preparation

1×ESP8266 NodeMCU
1×Micro USB Cable
1×(Optional) ESP8266 Screw Terminal Adapter

Or you can buy the following sensor kits:

1×DIYables Sensor Kit (30 sensors/displays)
1×DIYables Sensor Kit (18 sensors/displays)
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What is ESP8266 Websocket?

Now, you might be asking, "What's WebSocket?" It's pretty simple: WebSocket is a technology that lets a web browser talk directly to a web server in real-time.

  • Without WebSocket, you have to refresh the webpage to get updates. That's not very convenient.
  • With WebSocket, the webpage and the server stay connected all the time. This means they can share information instantly without having to reload the page.

You probably run into WebSocket in everyday web apps like online games, instant messaging, and stock market updates.

Why we need WebSocket to smoothly control ESP8266?

Imagine you want to control your remote-controlled car using a web interface on your phone or computer. Without WebSocket, every time you want to change the car's direction or speed, you'd need to refresh the web page. It's like having to press a "reload" button each time you want your command to reach the car.

Now, with WebSocket, it's like having a continuous and direct connection between your phone or computer and the car. You no longer need to refresh the page every time you want to steer the car or adjust its speed. It's as if the car is always listening to your commands in real-time, without any delays caused by constant page reloading.

In general, WebSocket allows you to:

  • Send data from the web browser to ESP8266 without reloading the webpage.
  • Send data from ESP8266 to the web browser without reloading the webpage.

This enables two-way communication in real-time manner.

Benefits of WebSocket with ESP8266:

  • Real-Time Control: WebSocket enables instant communication with the ESP8266, ensuring quick responses to commands for a seamless user experience.
  • Persistent Connection: Maintain a continuous link without refreshing the control page, creating an always-ready line of communication for immediate instructions.
  • Efficiency: Experience prompt responses without the need for constant page reloading, enhancing overall user enjoyment and efficiency.

Web Chat with ESP8266 via WebSocket

The webpage's content (HTML, CSS, JavaScript) are stored separately on an index.h file. So, we will have two code files on Arduino IDE:

  • An .ino file that is ESP8266 code, which creates a web sever and WebSocket server
  • An .h file, which contains the webpage's content.

Detailed Instructions

  • If this is the first time you use ESP8266, see how to setup environment for ESP8266 on Arduino IDE.
  • Connect the ESP8266 board to your PC via a micro USB cable
  • Open Arduino IDE on your PC.
  • Select the right ESP8266 board (e.g. ESP8266 Dev Module) and COM port.
  • Open the Library Manager by clicking on the Library Manager icon on the left navigation bar of Arduino IDE.
  • Search “WebSockets”, then find the WebSockets created by Markus Sattler.
  • Click Install button to install WebSockets library.
ESP8266 NodeMCU WebSockets library
  • On Arduino IDE, create new sketch, Give it a name, for example,
  • Copy the below code and open with Arduino IDE
/* * This ESP8266 NodeMCU code was developed by * * This ESP8266 NodeMCU code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * */ #include <ESP8266WiFi.h> #include <ESP8266WebServer.h> #include <WebSocketsServer.h> #include "index.h" const char* ssid = "YOUR_WIFI_SSID"; // CHANGE IT const char* password = "YOUR_WIFI_PASSWORD"; // CHANGE IT ESP8266WebServer server(80); // Web server on port 80 WebSocketsServer webSocket = WebSocketsServer(81); // WebSocket server on port 81 void webSocketEvent(uint8_t num, WStype_t type, uint8_t* payload, size_t length) { switch (type) { case WStype_DISCONNECTED: Serial.printf("[%u] Disconnected!\n", num); break; case WStype_CONNECTED: { IPAddress ip = webSocket.remoteIP(num); Serial.printf("[%u] Connected from %d.%d.%d.%d\n", num, ip[0], ip[1], ip[2], ip[3]); } break; case WStype_TEXT: Serial.printf("[%u] Received text: %s\n", num, payload); // Send a response back to the client String echoMessage = "Received: " + String((char*)payload); webSocket.sendTXT(num, echoMessage); break; } } void setup() { Serial.begin(9600); delay(500); // Connect to Wi-Fi WiFi.begin(ssid, password); while (WiFi.status() != WL_CONNECTED) { delay(1000); Serial.println("Connecting to WiFi..."); } Serial.println("Connected to WiFi"); // Initialize WebSocket server webSocket.begin(); webSocket.onEvent(webSocketEvent); // Serve a basic HTML page with JavaScript to create the WebSocket connection server.on("/", HTTP_GET, []() { Serial.println("Web Server: received a web page request"); String html = HTML_CONTENT; // Use the HTML content from the index.h file server.send(200, "text/html", html); }); server.begin(); Serial.print("ESP8266 Web Server's IP address: "); Serial.println(WiFi.localIP()); } void loop() { // Handle client requests server.handleClient(); // Handle WebSocket events webSocket.loop(); // TODO: Your code here }
  • Create the index.h file On Arduino IDE by:
    • Either click on the button just below the serial monitor icon and choose New Tab, or use Ctrl+Shift+N keys.
    Arduino IDE 2 adds file
    • Give the file's name index.h and click OK button
    Arduino IDE 2 adds file index.h
    • Copy the below code and paste it to the index.h.
    /* * This ESP8266 NodeMCU code was developed by * * This ESP8266 NodeMCU code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * */ const char *HTML_CONTENT = R"=====( <!DOCTYPE html> <!-- saved from url=(0019) --> <html><head><meta http-equiv="Content-Type" content="text/html; charset=windows-1252"> <title>ESP8266 WebSocket</title> <meta name="viewport" content="width=device-width, initial-scale=0.7"> <link rel="icon" href=""> <style> /* Add some basic styling for the chat window */ body { font-size: 16px; } .chat-container { width: 400px; margin: 0 auto; padding: 10px; } .chat-messages { height: 250px; overflow-y: auto; border: 1px solid #444; padding: 5px; margin-bottom: 5px; } .user-input { display: flex; margin-bottom: 20px; } .user-input input { flex: 1; border: 1px solid #444; padding: 5px; } .user-input button { margin-left: 5px; background-color: #007bff; color: #fff; border: none; padding: 5px 10px; cursor: pointer; } .websocket { display: flex; align-items: center; margin-bottom: 5px; } .websocket button { background-color: #007bff; color: #fff; border: none; padding: 5px 10px; cursor: pointer; } .websocket .label { margin-left: auto; } </style> <script> var ws; var wsm_max_len = 4096; /* bigger length causes uart0 buffer overflow with low speed smart device */ function update_text(text) { var chat_messages = document.getElementById("chat-messages"); chat_messages.innerHTML += text + '<br>'; chat_messages.scrollTop = chat_messages.scrollHeight; } function send_onclick() { if(ws != null) { var message = document.getElementById("message").value; if (message) { document.getElementById("message").value = ""; ws.send(message + "\n"); update_text('<span style="color:navy">' + message + '</span>'); // You can send the message to the server or process it as needed } } } function connect_onclick() { if(ws == null) { ws = new WebSocket("ws://" + + ":81"); document.getElementById("ws_state").innerHTML = "CONNECTING"; ws.onopen = ws_onopen; ws.onclose = ws_onclose; ws.onmessage = ws_onmessage; } else ws.close(); } function ws_onopen() { document.getElementById("ws_state").innerHTML = "<span style='color:blue'>CONNECTED</span>"; document.getElementById("bt_connect").innerHTML = "Disconnect"; document.getElementById("chat-messages").innerHTML = ""; } function ws_onclose() { document.getElementById("ws_state").innerHTML = "<span style='color:gray'>CLOSED</span>"; document.getElementById("bt_connect").innerHTML = "Connect"; ws.onopen = null; ws.onclose = null; ws.onmessage = null; ws = null; } function ws_onmessage(e_msg) { e_msg = e_msg || window.event; // MessageEvent console.log(; update_text('<span style="color:blue">' + + '</span>'); } </script> </head> <body> <div class="chat-container"> <h2>ESP8266 WebSocket</h2> <div class="websocket"> <button class="connect-button" id="bt_connect" onclick="connect_onclick()">Connect</button> <span class="label">WebSocket: <span id="ws_state"><span style="color:blue">CLOSED</span></span></span> </div> <div class="chat-messages" id="chat-messages"></div> <div class="user-input"> <input type="text" id="message" placeholder="Type your message..."> <button onclick="send_onclick()">Send</button> </div> <div class="sponsor">Sponsored by <a href="">DIYables</a></div> </div> </body></html> )=====";
    • Modify the WiFi information (SSID and password) in the code to match your own network credentials.
    • Now you have the code in two files: and index.h
    • Click Upload button on Arduino IDE to upload code to ESP8266.
    • Open the Serial Monitor
    • Check out the result on Serial Monitor.
    Connecting to WiFi... Connected to WiFi ESP8266 Web Server's IP address IP address:
    Autoscroll Show timestamp
    Clear output
    9600 baud  
    • Take note of the IP address displayed, and enter this address into the address bar of a web browser on your smartphone or PC.
    • You will see the webpage it as below:
    ESP8266 NodeMCU websocket web browser
    • Click the CONNECT button to connect the webpage to ESP8266 via WebSocket.
    • Type some words and send them to ESP8266.
    • You will see the response from ESP8266.
    ESP8266 NodeMCU websocket chat server

    ※ NOTE THAT:

    • If you modify the HTML content in the index.h and does not touch anything in file, when you compile and upload code to ESP8266, Arduino IDE will not update the HTML content.
    • To make Arduino IDE update the HTML content in this case, make a change in the file (e.g. adding empty line, add a comment....)

    Line-by-line Code Explanation

    The above ESP8266 code contains line-by-line explanation. Please read the comments in the code!

How the System Operates

The ESP8266 code functions by creating both a web server and a WebSocket Server. The process unfolds as follows:

  • When you input the ESP8266's IP address into a web browser, a request is made for the webpage (User Interface) from the ESP8266.
  • The ESP8266's web server responds by transmitting the content of the webpage (HTML, CSS, JavaScript).
  • Subsequently, your web browser displays the webpage.
  • When you click the CONNECT button, the JavaScript code embedded in the webpage establishes a WebSocket connection to the WebSocket server on the ESP8266.
  • With the WebSocket connection established, when you type something and click the SEND button, the JavaScript code send that text to to the ESP8266 through the WebSocket connection in the background.
  • Upon receiving the angle value, the WebSocket server sends back a reply to the webpage.

You can learn other ESP8266 WebSocket examples below:


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