WebSocket Echo Server - Free Testing Tool for Real-Time Applications

Overview

The WebSocket Echo Server at echo.websocket.org is a free, publicly available testing endpoint that has become an essential tool for developers working with real-time web technologies. This server provides instant echo responses for WebSocket connections, Server-Sent Events (SSE), and standard HTTP requests, making it invaluable for testing, debugging, and validating real-time implementations.

Unlike production WebSocket servers that implement complex business logic, our echo server provides a clean, predictable environment where every message sent is immediately echoed back. This simplicity makes it perfect for isolating connection issues, testing client libraries, validating proxy configurations, and debugging protocol-level problems.

Key Features

Multi-Protocol Support

The echo server supports three primary protocols, each accessible through different endpoints:

WebSocket Protocol: Full-duplex communication at wss://echo.websocket.org
Server-Sent Events: One-way streaming at https://echo.websocket.org/.sse
HTTP Echo: Standard HTTP request/response at any other path
Browser UI: Interactive testing interface at https://echo.websocket.org/.ws

Testing Capabilities

Our echo server excels at several testing scenarios:

Connection Testing: Verify WebSocket handshake and connection establishment
Message Round-Trip: Test message sending and receiving with guaranteed echo
Proxy Validation: Confirm WebSocket traffic passes through corporate proxies
Library Testing: Validate WebSocket client library implementations
Performance Testing: Measure round-trip latency and throughput
Protocol Debugging: Inspect frames and connection behavior

How to Use the Echo Server

Quick WebSocket Test with JavaScript

Here’s a simple example to test the WebSocket echo server from any browser console:

// Connect to the WebSocket echo server
const socket = new WebSocket('wss://echo.websocket.org');

// Connection opened
socket.addEventListener('open', (event) => {
  console.log('Connected to echo server');

  // Send a test message
  socket.send('Hello, WebSocket Echo Server!');

  // Send JSON data
  socket.send(
    JSON.stringify({
      type: 'test',
      timestamp: Date.now(),
      message: 'Testing echo functionality',
    })
  );
});

// Listen for echoed messages
socket.addEventListener('message', (event) => {
  console.log('Echoed back:', event.data);

  // Parse JSON if needed
  try {
    const data = JSON.parse(event.data);
    console.log('Received JSON:', data);
  } catch (e) {
    console.log('Received text:', event.data);
  }
});

// Handle errors
socket.addEventListener('error', (event) => {
  console.error('WebSocket error:', event);
});

// Connection closed
socket.addEventListener('close', (event) => {
  console.log('Disconnected from echo server');
  console.log('Close code:', event.code);
  console.log('Close reason:', event.reason);
});

Testing with Command Line Tools

You can also test the echo server using command-line tools like wscat:

# Install wscat globally
npm install -g wscat

# Connect to the echo server
wscat -c wss://echo.websocket.org

# Type messages and see them echoed back
> Hello from wscat!
< Hello from wscat!

Server-Sent Events Testing

For SSE testing, you can use this JavaScript example:

// Create EventSource connection
const eventSource = new EventSource('https://echo.websocket.org/.sse');

// Listen for messages
eventSource.onmessage = (event) => {
  console.log('SSE message received:', event.data);
};

// Handle connection open
eventSource.onopen = () => {
  console.log('SSE connection established');
};

// Handle errors
eventSource.onerror = (error) => {
  console.error('SSE error:', error);
  if (eventSource.readyState === EventSource.CLOSED) {
    console.log('SSE connection closed');
  }
};

Technical Specifications

Connection Details

Protocol: WebSocket Protocol Version 13 (RFC 6455)
Secure Connection: TLS 1.2+ required for WSS
Maximum Message Size: 64 KB per message
Timeout: Connections timeout after 10 minutes of inactivity
Concurrent Connections: Reasonable limits apply to prevent abuse

Endpoint Behavior

The echo server implements these specific behaviors:

Immediate Echo: Messages are echoed back with minimal latency
Message Preservation: Binary and text messages maintain their type
No Message History: Each connection is independent with no persistence
Clean Close: Proper WebSocket close handshake on disconnection