Getting started with k6 is a practical first step toward mastering API performance testing. This open-source tool lets you write and run load tests using JavaScript. Because it is lightweight, scriptable, and CI-friendly, many QA engineers and developers choose k6 to ensure their APIs can handle traffic smoothly.

In this blog, you’ll learn how to install k6, write your first script, run the test, and interpret the results. Let’s begin!

Why Use k6 for Performance Testing?

k6 simplifies performance testing by allowing you to use JavaScript, a language most developers are already familiar with. Moreover, it supports integrations with CI/CD tools, making it easy to automate tests as part of your pipeline.

In addition, k6 is open-source and has a strong community backing. The CLI output is clear, and the tool is built to simulate real-world user behavior efficiently.

Installing k6

To start, install k6 on your system. Use the following commands based on your operating system:

# macOS
brew install k6

# Windows
choco install k6

# Ubuntu/Linux
sudo apt install k6

If you prefer Docker or want to install it manually, you can follow the official installation guide.

Writing Your First Script

After installation, create a new file named script.js. Add the following test script:

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

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

export default function () {
  const res = http.get('https://test-api.k6.io/');
  check(res, {
    'status is 200': (r) => r.status === 200,
  });
  sleep(1);
}

Let’s break this down:

• The script sends a GET request to a public test API.
• It simulates 10 virtual users active for 30 seconds.
• A check ensures that the server returns a status code of 200.
• Finally, the sleep(1) call adds a 1-second delay between requests.

This setup mimics real user behavior and provides a basic, yet powerful, load test.

k6 run script.js

k6 run --out json=results.json script.js