Introduction

K6 is an open-source load testing tool used to test the performance and stability of APIs, websites, and applications.
It is lightweight, developer-friendly, and uses JavaScript for writing test scripts.

K6 helps to:

• Test API performance
• Simulate multiple users
• Identify bottlenecks
• Measure response times
• Validate application scalability

Prerequisites

Before installing K6, ensure the following requirements are available:

• Linux / Windows / macOS server
• Internet connection
• Basic terminal knowledge
• Access to the application or API

Example test target:

https://example.com

Implementation

I. K6 Installation

(i) Install K6 on Ubuntu / Debian

sudo apt update

sudo apt install -y gnupg software-properties-common

curl -fsSL https://dl.k6.io/key.gpg | sudo gpg --dearmor -o /usr/share/keyrings/k6-archive-keyring.gpg

echo "deb [signed-by=/usr/share/keyrings/k6-archive-keyring.gpg] https://dl.k6.io/deb stable main" | sudo tee /etc/apt/sources.list.d/k6.list

sudo apt update

sudo apt install k6 -y

(ii) Verify Installation

k6 version

Example output:

k6 v0.48.0

II. Basic K6 Test Script

Create a file:

test.js

Add the following script:

import http from 'k6/http';
import { sleep } from 'k6';

export default function () {

    http.get('https://example.com');

    sleep(1);
}

III. Run the Test

k6 run test.js

IV. API Load Test Example

import http from 'k6/http';
import { check, sleep } from 'k6';

export const options = {
    vus: 10,
    duration: '30s',
};

export default function () {

    let response = http.get('https://example.com/api/users');

    check(response, {
        'status is 200': (r) => r.status === 200,
    });

    sleep(1);
}

V. POST Request Example

import http from 'k6/http';

export default function () {

    const payload = JSON.stringify({
        username: 'testuser',
        password: 'password123'
    });

    const params = {
        headers: {
            'Content-Type': 'application/json',
        },
    };

    http.post('https://example.com/api/login', payload, params);
}

VI. Stress Test Example

import http from 'k6/http';

export const options = {
    stages: [
        { duration: '30s', target: 20 },
        { duration: '1m', target: 100 },
        { duration: '30s', target: 0 },
    ],
};

export default function () {

    http.get('https://example.com');
}

VII. Save Test Results

k6 run test.js --out json=result.json

VIII. Generate HTML Report

k6 run test.js --summary-export=summary.json

Notes

IX. Advantages of K6

• Easy JavaScript scripting
• Lightweight and fast
• Supports API and website testing
• Good CLI output
• Supports CI/CD integration
• Open-source

Conclusion

K6 is a simple and powerful load testing tool for testing APIs and web applications.
It allows teams to simulate user traffic, monitor application performance, and identify issues before production deployment.