The Ultimate Guide to Websocket Opcode 9: Everything You Need to Know


WebSocket is a powerful technology that enables two-way communication between a client and a server over a single, long-lived connection. It is widely used for building real-time web applications, such as chat applications, online gaming platforms, and collaborative tools. WebSocket uses a protocol that defines a set of message types, or opcodes, that clients and servers can use to communicate. One of the most important opcodes is opcode 9. In this article, we will provide a comprehensive guide to WebSocket opcode 9, including its definition, use cases, and best practices.

What is Websocket Opcode 9?

WebSocket opcode 9, also known as the “ping” opcode, is a special type of message that clients can send to servers to check if the connection is still alive. When a client sends a ping message, the server must respond with a pong message to acknowledge that the connection is still active. If the server does not respond within a certain timeframe, the client assumes that the connection has been lost and can take appropriate action, such as trying to reconnect or displaying an error message.

The ping/pong mechanism is essential for ensuring the reliability and stability of WebSocket connections, especially when dealing with unreliable networks or long periods of inactivity. Without it, clients and servers would have no way of knowing if the other end is still there and would have to rely on timeouts or other unreliable mechanisms to detect disconnections.

How to Use Websocket Opcode 9?

Using WebSocket opcode 9 is relatively simple. Clients can send ping messages to servers by setting the opcode field of the message to 9 and including any payload data they want to send. The payload data is optional and can be used for various purposes, such as sending a timestamp or a nonce to prevent caching.

Here’s an example of how to send a ping message using JavaScript:

var socket = new WebSocket("ws://");socket.onopen = function() {setInterval(function() {socket.send(JSON.stringify({opcode: 9,payload: "ping",}));}, 5000);};socket.onmessage = function(event) {var message = JSON.parse(;if (message.opcode === 10) {console.log("Received pong message");}};

This code creates a new WebSocket connection to a server and sends a ping message every 5 seconds. When the server responds with a pong message, the client logs a message to the console.

Servers that support WebSocket opcode 9 must respond to ping messages with a pong message that has the same payload data as the original ping message, if any. The pong message should have an opcode of 10 and should be sent as soon as possible, ideally within a few milliseconds. Here’s an example of how to handle ping messages in Node.js:

var WebSocketServer = require('ws').Server;var wss = new WebSocketServer({ port: 8080 });wss.on('connection', function(ws) {ws.on('message', function(message) {var data = JSON.parse(message);if (data.opcode === 9) {ws.send(JSON.stringify({opcode: 10,payload: data.payload,}));}});});

This code creates a new WebSocket server that listens on port 8080 and responds to ping messages with pong messages. When a client sends a ping message, the server extracts the payload data, creates a new pong message with the same payload data, and sends it back to the client.

Best Practices for Using Websocket Opcode 9

While WebSocket opcode 9 is a useful feature, it can also cause problems if used improperly. Here are some best practices to follow when using opcode 9:

  1. Use ping messages sparingly: Ping messages can consume network resources and increase latency, especially if sent too frequently. Only use ping messages when necessary, such as when detecting disconnections or measuring latency.
  2. Set a reasonable ping interval: The interval between ping messages should be long enough to avoid overloading the network but short enough to detect disconnections in a timely manner. A good starting point is 30 seconds, but this can vary depending on the application’s requirements.
  3. Handle ping/pong timeouts: If a ping message is not answered within a certain timeframe, the client should assume that the connection has been lost and take appropriate action, such as trying to reconnect or displaying an error message. Similarly, if a pong message is not received within a reasonable time, the server should assume that the client has disconnected and close the connection.
  4. Consider using other opcodes: While ping/pong messages are the most common way to check for connection reliability, there are other opcodes that can be used for similar purposes. For example, opcode 8 (close) can be used to signal a graceful shutdown of the connection, while opcode 2 (binary) can be used to send large data payloads.
  5. Test with different network conditions: WebSocket connections can behave differently under different network conditions, such as high latency or packet loss. It’s important to test your application with different network conditions to ensure that it works reliably in all scenarios.


What happens if a client sends multiple ping messages before receiving a pong message?

If a client sends multiple ping messages before receiving a pong message, the server should respond to each ping message with a separate pong message. The order of the pong messages does not matter, as long as each pong message has the same payload data as the corresponding ping message.

Can ping messages be used for load balancing?

No, ping messages are not suitable for load balancing because they do not carry any information about the client’s state or the server’s load. Load balancing should be done using other mechanisms, such as DNS round-robin or IP hash.

What is the difference between WebSocket opcode 9 and HTTP keep-alive?

WebSocket opcode 9 and HTTP keep-alive are both mechanisms for keeping a connection alive between a client and a server. However, HTTP keep-alive is a feature of the HTTP protocol that allows multiple requests to be sent over a single TCP connection, while WebSocket opcode 9 is a specific message type within the WebSocket protocol. WebSocket opcode 9 is more efficient than HTTP keep-alive because it does not require the overhead of HTTP headers and can be used for bidirectional communication.


WebSocket opcode 9 is an essential feature of the WebSocket protocol that enables clients and servers to check for connection reliability and stability. By using ping/pong messages, developers can build real-time web applications that work reliably and efficiently under different network conditions. However, it’s important to follow best practices and test your application thoroughly to ensure that it works as expected.