Load Testing & Performance Benchmarking (JMeter & k6) · Lesson

Writing Basic k6 Scripts

Create your first k6 script to send HTTP requests and simulate virtual users.

Writing Basic k6 Scripts is a free Load Testing & Performance Benchmarking (JMeter & k6) lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Load Testing & Performance Benchmarking (JMeter & k6) learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Start Your k6 Script Journey

Welcome to writing k6 scripts! k6 uses JavaScript to define your load tests, making it familiar for many developers.

A k6 script describes what your virtual users will do and how the load should be simulated.

Define user actions like visiting pages or logging in.
Specify the number of virtual users (VUs) and test duration.
Validate server responses to ensure correctness.

Anatomy of a k6 Script

Every k6 script typically has two main parts:

The options object: Here you configure test-wide settings like virtual users (VUs) and test duration.
The default function: This is where your virtual users' actions are defined. It's executed repeatedly by each VU.

Think of the default function as the "main loop" for each virtual user.

Sending HTTP GET Requests

The most common action in a performance test is sending an HTTP request. k6 provides the k6/http module for this.

To send a simple GET request, you'll use http.get('URL'). This simulates a browser fetching a web page or an API endpoint.

Remember to import the http module at the top of your script.

Code: Basic GET Request

Let's write our first k6 script to make a GET request to example.com. Copy and run this script using the k6 CLI.

k6 run your_script.js

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

export default function () {
  http.get('https://test.k6.io');
  sleep(1); // Wait for 1 second between requests
}

What are Virtual Users (VUs)?

In k6, a Virtual User (VU) simulates a real user interacting with your system. Each VU executes the default function independently.

If you have 10 VUs, it's like 10 people simultaneously using your application. k6 efficiently manages these VUs.

By controlling the number of VUs, you can simulate different levels of load on your application.

Configuring Test Load with Options

The options object is crucial for defining your test scenario. It sits at the top level of your script.

Two key options are:

vus: The total number of virtual users to run concurrently.
duration: How long the test should run (e.g., '30s', '5m', '2h').

These settings tell k6 how to distribute and execute your default function.

Code: VUs and Test Duration

This script runs with 5 virtual users for a duration of 10 seconds, hitting the test website repeatedly.

Observe how k6 reports the VUs and duration when you run this script.

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

export const options = {
  vus: 5,
  duration: '10s',
};

export default function () {
  http.get('https://test.k6.io');
  sleep(1);
}

Sending Data with POST Requests

Beyond GET, you often need to send data to the server, like submitting a form or creating a resource. For this, you use http.post().

The http.post() function takes three arguments:

The URL.
The request body (usually a JSON string or form data).
Optional parameters like headers.

Code: Simple POST Request

Here's an example of a POST request sending JSON data. Notice how we specify the Content-Type header to tell the server we're sending JSON.

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

export const options = {
  vus: 1,
  duration: '5s',
};

export default function () {
  const url = 'https://httpbin.org/post';
  const payload = JSON.stringify({
    name: 'Coddy',
    job: 'Learner',
  });

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

  http.post(url, payload, params);
  sleep(1);
}

Test Your Scripting Skills

Which of the following statements about basic k6 scripting are TRUE?

Recap: Your First k6 Scripts

Great job! You've learned the fundamentals of writing k6 scripts:

The basic structure with options and the default function.
How to send simple HTTP GET and POST requests using k6/http.
Configuring test load with vus and duration.

In the next lesson, we'll dive into validating responses with Checks and setting performance targets with Thresholds!

Frequently asked questions

Is the “Writing Basic k6 Scripts” lesson free?

Yes — the full text of “Writing Basic k6 Scripts” is free to read here on the web, and the Load Testing & Performance Benchmarking (JMeter & k6) course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Load Testing & Performance Benchmarking (JMeter & k6) course, upgrade to CoddyKit PRO.

What will I learn in “Writing Basic k6 Scripts”?

Create your first k6 script to send HTTP requests and simulate virtual users. You practise Load Testing & Performance Benchmarking (JMeter & k6) with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Load Testing & Performance Benchmarking (JMeter & k6)?

No prior experience is required. Load Testing & Performance Benchmarking (JMeter & k6) on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Writing Basic k6 Scripts” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Load Testing & Performance Benchmarking (JMeter & k6) lesson?

Yes. Every Load Testing & Performance Benchmarking (JMeter & k6) lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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