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Browser Testing Overview

The k6 browser module brings browser automation and end-to-end web testing to k6 while supporting core k6 features. It adds browser-level APIs to interact with browsers and collect frontend performance metrics as part of your k6 tests.
To work with the browser module, make sure you are using the latest k6 version, and install a Chromium-based browser on your machine (such as Google Chrome).

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Why Browser Testing?

Browser-level testing provides a way to measure user experience and find issues that are difficult to catch on the protocol level. Browser testing helps you answer questions like:
  • When my application receives thousands of simultaneous requests from the protocol-level, what happens to the frontend?
  • How can I get metrics specific to browsers, like total page load time?
  • Are all my elements interactive on the frontend?
  • Are there any loading spinners that take a long time to disappear?

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Key Features

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Real Browser Automation

The browser module uses Chromium to simulate real user interactions:
  • Navigate to pages and click elements
  • Fill out forms and submit data
  • Take screenshots and capture metrics
  • Verify page content and UI elements

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Web Vitals Metrics

k6 browser automatically collects Core Web Vitals metrics:
  • FCP (First Contentful Paint) - Loading performance
  • LCP (Largest Contentful Paint) - Main content rendering
  • CLS (Cumulative Layout Shift) - Visual stability
  • FID (First Input Delay) - Interactivity
  • INP (Interaction to Next Paint) - Responsiveness
  • TTFB (Time to First Byte) - Server response time

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Hybrid Performance Testing

Combine browser tests with protocol-level tests in a single script to:
  • Test real user flows on the frontend while generating higher load in the backend
  • Measure both backend and frontend performance in the same test execution
  • Increase collaboration between backend and frontend teams

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Quick Start

Create a browser test using the k6 CLI: 
k6 new --template browser browser-script.js
Run the test: 
k6 run browser-script.js

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Example Browser Test

Here’s a simple browser test that navigates to a page and takes a screenshot: 
import { browser } from 'k6/browser';

export const options = {
  scenarios: {
    ui: {
      executor: 'shared-iterations',
      options: {
        browser: {
          type: 'chromium',
        },
      },
    },
  },
};

export default async function () {
  const page = await browser.newPage();

  try {
    await page.goto('https://test.k6.io/');
    await page.screenshot({ path: 'screenshot.png' });
  } finally {
    await page.close();
  }
}

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Browser Metrics Output

After running a browser test, k6 displays browser-specific metrics: 
BROWSER
browser_data_received.........: 357 kB 54 kB/s
browser_data_sent.............: 4.9 kB 738 B/s
browser_http_req_duration.....: avg=355.28ms min=124.04ms med=314.4ms
browser_http_req_failed.......: 0.00%  0 out of 18

WEB_VITALS
browser_web_vital_cls.........: avg=0        min=0        med=0
browser_web_vital_fcp.........: avg=2.33s    min=2.33s    med=2.33s
browser_web_vital_fid.........: avg=300µs    min=300µs    med=300µs
browser_web_vital_inp.........: avg=56ms     min=56ms     med=56ms
browser_web_vital_lcp.........: avg=2.33s    min=2.33s    med=2.33s
browser_web_vital_ttfb........: avg=1.45s    min=1.45s    med=1.45s

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Use Cases

1
End-to-End Testing
2
Validate critical user journeys by simulating real browser interactions from login to checkout.
3
Frontend Performance
4
Monitor Web Vitals and frontend performance under different load conditions.
5
Hybrid Load Testing
6
Combine a small number of browser VUs with many protocol-level VUs for comprehensive testing.
7
Regression Testing
8
Detect frontend regressions by running browser tests in your CI/CD pipeline.

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Next Steps

Getting Started

Write your first k6 browser test

How to Write Tests

Learn browser testing concepts and patterns

Best Practices

Optimize your browser tests for reliability

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