Real-time features are no longer optional. Chat apps, live tracking, notifications, collaborative editors — all of them rely on WebSockets to push data instantly.
Yet, many engineers struggle with two things:
How do I actually build a WebSocket server? 1.
How do I test it properly without writing a full frontend?
In this post, we’ll do both — build a WebSocket server from scratch and test it using Postman, step by step.
This guide is practical, beginner-friendly, and grounded in real-world backend engineering.
How to prevent Double Booking in Distributed System 1.
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Real-time features are no longer optional. Chat apps, live tracking, notifications, collaborative editors — all of them rely on WebSockets to push data instantly.
Yet, many engineers struggle with two things:
How do I actually build a WebSocket server? 1.
How do I test it properly without writing a full frontend?
In this post, we’ll do both — build a WebSocket server from scratch and test it using Postman, step by step.
This guide is practical, beginner-friendly, and grounded in real-world backend engineering.
How to prevent Double Booking in Distributed System 1.
𝗦𝗰𝗮𝗹𝗮𝗯𝗶𝗹𝗶𝘁𝘆 𝗶𝗻 𝗦𝘆𝘀𝘁𝗲𝗺 𝗗𝗲𝘀𝗶𝗴𝗻 — 𝗗𝗲𝘁𝗮𝗶𝗹𝗲𝗱 𝗡𝗼𝘁𝗲𝘀 for Interview 1.
Designing a Robust Distributed Logging System for Modern Applications 1.
System Design: The Distributed Task Scheduler 1.
10 System design trade-offs 1.
Rate Limiting Algorithms Explained with Code 1.
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How Shopify handles 16,000 Request per second 1.
Software Architecture Pattern - Layered Architecture 1.
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Microservices Design Pattern - Event Sourcing Pattern 1.
Distributed System Learning Roadmap 1.
15 Scaling Techniques in Distributed Systems 1.
WebSocket is a protocol that provides:
A persistent connection between client and server
Bi-directional communication (server can push data anytime)
Much lower latency than HTTP polling
Once connected:
Client ⇄ WebSocket Connection ⇄ Server
This makes WebSockets ideal for real-time systems.
We’ll use Node.js with the popular ws library.
mkdir websocket-demo
cd websocket-demo
npm init -y
npm install ws
Create a file called server.js.
const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 8080 });
console.log('WebSocket server running on ws://localhost:8080');
wss.on('connection', (ws, req) => {
console.log('Client connected');
// Send welcome message
ws.send(JSON.stringify({
type: 'WELCOME',
message: 'Connected to WebSocket server'
}));
ws.on('message', (data) => {
const message = data.toString();
console.log('Received:', message);
// Echo message back
ws.send(JSON.stringify({
type: 'ECHO',
message
}));
});
ws.on('close', () => {
console.log('Client disconnected');
});
});
Start the server:
node server.js
Your WebSocket backend is now live.
Traditionally, Postman was used only for REST APIs. Today, it supports WebSocket testing natively, which is incredibly useful for backend engineers.
Postman helps you:
Test WebSocket connections without a UI
Debug message formats
Validate authentication logic
Simulate multiple clients
Open Postman 1.
Click New → WebSocket Request 1.
Enter the URL:
ws://localhost:8080
Click Connect
If the connection succeeds, you’ll immediately see the welcome message from the server.
In the message input box, send:
Hello WebSocket
The server responds with:
{
"type": "ECHO",
"message": "Hello WebSocket"
}
This confirms that:
The connection is active
Messages are flowing correctly
Server-side logic works
In real systems, WebSocket messages should always be structured.
Example message:
{
"type": "CHAT_MESSAGE",
"userId": "postman-user",
"payload": {
"text": "Hello from Postman"
}
}
Update the server to parse JSON safely:
ws.on('message', (data) => {
try {
const msg = JSON.parse(data.toString());
console.log('Received JSON:', msg);
} catch (err) {
console.log('Received text:', data.toString());
}
});
This pattern scales far better than plain strings.
Open multiple WebSocket requests in Postman and connect them to the same server.
Send a message from one client. If your server broadcasts messages, all connected clients will receive it.
This is crucial for testing:
Chat applications
Live dashboards
Notification systems
Most production WebSocket systems require authentication.
Add this header in Postman before connecting:
Authorization: Bearer <JWT_TOKEN>
On the server:
wss.on('connection', (ws, req) => {
const token = req.headers['authorization'];
console.log('Auth header:', token);
});
ws://localhost:8080?token=abc123
Both approaches are easy to validate using Postman.
WebSocket connections can silently die. A heartbeat mechanism helps detect dead clients.
setInterval(() => {
wss.clients.forEach(ws => {
if (ws.readyState === WebSocket.OPEN) {
ws.ping();
}
});
}, 30000);
Postman automatically responds with pong, making it perfect for testing this logic.
Treating WebSockets like REST APIs
Sending unstructured messages
Ignoring connection lifecycle
Not testing multiple clients
Postman helps catch these issues early.
Building WebSocket systems doesn’t have to be complicated.
With a minimal server and Postman as your testing tool, you can confidently develop, debug, and validate real-time features — long before a frontend exists.
If you’re building chat systems, live tracking, or event-driven platforms, this workflow will quickly become indispensable.
Coming next:
Scaling WebSockets with Redis Pub/Sub
Handling race conditions in real-time systems
WebSocket vs SSE vs gRPC streaming