k6 Tutorial — Modern Load Testing in JavaScript (2026)

Last updated 2026-07-20 · 12 min read · By Avinash K

k6 replaced JMeter as the default load-test tool for cloud-native teams because scripts are JavaScript, results stream to Grafana, and one binary runs anywhere. This tutorial takes you from install to a production CI pipeline with meaningful thresholds.

Key takeaways

• Install k6 and run your first load test in 5 minutes.
• Stages, VUs, and iterations — the model you must understand.
• Thresholds and checks — how to fail a build on p95 latency.
• Output to Grafana Cloud and integrate into GitHub Actions.

brew install k6         # macOS
choco install k6        # Windows
sudo apt install k6     # Debian/Ubuntu

# script.js
import http from 'k6/http';
import { check, sleep } from 'k6';

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

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

# run
k6 run script.js

export const options = {
  stages: [
    { duration: '2m', target: 100 },   // ramp to 100 VUs
    { duration: '5m', target: 100 },   // hold
    { duration: '2m', target: 500 },   // spike
    { duration: '5m', target: 500 },   // hold
    { duration: '2m', target: 0 },     // ramp down
  ],
};

Match stages to a real user pattern. See our performance strategy guide for how to derive stages from prod metrics.

export const options = {
  thresholds: {
    http_req_failed: ['rate<0.01'],                 // < 1% errors
    http_req_duration: ['p(95)<500', 'p(99)<1500'], // p95 < 500ms
    checks: ['rate>0.99'],                          // 99% checks pass
  },
};

k6 exits non-zero when thresholds fail — perfect for CI gating.

export const options = {
  scenarios: {
    browse: { executor: 'ramping-vus', stages: [...], exec: 'browse' },
    checkout: { executor: 'constant-arrival-rate', rate: 10,
      timeUnit: '1s', duration: '5m', preAllocatedVUs: 20, exec: 'checkout' },
  },
};

export function browse() { http.get('/products'); }
export function checkout() { http.post('/orders', payload); }

# Local Grafana + InfluxDB
k6 run --out influxdb=http://localhost:8086/k6 script.js

# Grafana Cloud k6
K6_CLOUD_TOKEN=... k6 cloud script.js

# GitHub Actions
- uses: grafana/k6-action@v0.3.1
  with:
    filename: script.js
    flags: --out cloud

See the official k6 docs and compare with JMeter to choose per project.