k6 Script Basics, Options and Thresholds

To use k6 effectively, you need to understand the basic script structure, options and thresholds that control when a test is considered successful. These concepts let you model load and define pass/fail criteria inline with your test code.

Script Structure, VUs and Duration #

A k6 script typically exports an options object that configures virtual users (VUs), duration and scenarios, plus a default function that runs for each VU. You can run simple constant-load tests by specifying vus and duration, or use more advanced scenario definitions.

export const options = {
  vus: 20,
  duration: '1m',
};

export default function () {
  // test logic here
}

Using Thresholds as Built-In Quality Gates #

Thresholds in k6 express performance goals directly in code—for example, requiring that the 95th percentile of a metric stays below a limit. If thresholds are violated, k6 exits with a non-zero status, which CI tools can treat as a failed job.

export const options = {
  vus: 50,
  duration: '2m',
  thresholds: {
    http_req_duration: ['p(95)<800', 'avg<400'],
    http_req_failed: ['rate<0.01'],
  },
};

With thresholds, performance expectations become part of your test definition rather than a separate document.

Common Mistakes #

Mistake 1 — Running k6 scripts without thresholds #

This loses pass/fail clarity.

❌ Wrong: Manually scanning metrics to decide if a run was acceptable.

✅ Correct: Encode key limits as thresholds so failures are explicit.

Mistake 2 — Treating VUs as a direct proxy for real users #

This oversimplifies behaviour.

❌ Wrong: Assuming “100 VUs equals 100 humans.”

✅ Correct: Interpret VUs in combination with request rates and think time.