# k6 — Modern Load Testing Tool Using Go and JavaScript

> k6 is a modern load testing tool built by Grafana Labs. Write test scripts in JavaScript, run them in a high-performance Go runtime. Developer-centric with CLI-first workflow, CI/CD integration, and Grafana Cloud for result analysis.

## Install

Save as a script file and run:

## Quick Use

```bash
brew install k6                             # macOS
sudo apt install k6                         # Debian/Ubuntu
docker run --rm -i grafana/k6 run - < script.js
```

```js
// load-test.js
import http from "k6/http";
import { check, sleep } from "k6";

export const options = {
  stages: [
    { duration: "30s", target: 50 },   // Ramp up to 50 VUs
    { duration: "1m",  target: 50 },   // Stay at 50
    { duration: "10s", target: 0 },    // Ramp down
  ],
  thresholds: {
    http_req_duration: ["p(95)<500"],   // 95th percentile < 500ms
    http_req_failed: ["rate<0.01"],     // Error rate < 1%
  },
};

export default function () {
  const res = http.get("https://api.tokrepo.com/assets");
  check(res, {
    "status is 200": (r) => r.status === 200,
    "body has assets": (r) => r.json().length > 0,
  });
  sleep(1);
}
```

```bash
k6 run load-test.js
k6 run --vus 100 --duration 2m load-test.js
```

## Intro

k6 is a modern load testing tool built by Grafana Labs. Write test scripts in JavaScript (ES6), execute them in a high-performance Go runtime (not Node.js). CLI-first, developer-friendly, with built-in metrics, thresholds, and CI/CD integration.

- **Repo**: https://github.com/grafana/k6
- **Stars**: 30K+
- **Language**: Go
- **License**: AGPL 3.0

## What k6 Does

- **JavaScript scripting** — ES6 modules for test logic
- **Go runtime** — high performance, low overhead
- **Virtual Users** — simulate concurrent users
- **Scenarios** — constant, ramping, arrival-rate
- **Thresholds** — pass/fail criteria for CI
- **Checks** — response assertions
- **Metrics** — request duration, throughput, errors
- **Protocols** — HTTP, WebSocket, gRPC, Redis
- **Extensions** — xk6 for custom protocols
- **Output** — JSON, CSV, Grafana Cloud, Prometheus, InfluxDB

## Comparison

| Tool | Scripts | Runtime | Distributed |
|---|---|---|---|
| k6 | JavaScript | Go | k6-operator |
| Locust | Python | Python | Built-in |
| JMeter | XML/GUI | Java | Built-in |
| Gatling | Scala | JVM | Paid |
| Artillery | YAML/JS | Node.js | Paid |

## FAQ

**Q: Why not Node.js?**
A: k6's JS engine is goja, embedded in Go (not V8/Node). This keeps per-VU overhead small, letting a single machine simulate thousands of VUs.

**Q: Grafana integration?**
A: Output to Prometheus Remote Write or Grafana Cloud k6, then view real-time load-testing metrics in a Grafana dashboard.

## Sources

- Docs: https://grafana.com/docs/k6
- GitHub: https://github.com/grafana/k6
- License: AGPL 3.0

---
Source: https://tokrepo.com/en/workflows/4240522f-364b-11f1-9bc6-00163e2b0d79
Author: Script Depot