A modern load testing tool, using Go and JavaScript

"like unit testing, for performance"

k6 is a modern load testing tool, building on Load Impact's years of experience. It provides a clean, approachable JavaScript scripting API, distributed and cloud execution, and orchestration via a REST API.

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Tags and Groups

The analysis of your load results is a required step to find performance issues; a load test usually targets a service involving different subsystems and resources, making it hard to find the issue/s degrading your performance.

k6 provides two scripting APIs to help you during the analysis and easily visualize, sort and filter your test results.

  • Groups: organize your load script around common logic.
  • Tags: categorize your checks, thresholds, custom metrics and requests with tags for in-depth filtering.


Groups are optional, and it allows you to “group” your load script. Groups can be nested, allowing you the BDD-style of testing.

import { group } from "k6";

export default function() {
  group(“user flow: returning user”, function() {
    group(“visit homepage”, function() {
      // load homepage resources
    group(“login”, function() {
      // perform login

Your test results will be grouped based on your group names for easily visualization.


Tags are a simple and powerful way to categorize your k6 entities for later results filtering.

k6 provides two types of tags:

  • User-defined tags: the ones you've added when writing your script.
  • System tags: tags automatically assigned by k6.

System tags

Currently, k6 automatically creates tags in the following categories:

  • URLs:
    • url:<your-url1>,
    • url:<your-url2>
    • ....
  • http methods:
    • method:GET
    • method:POST
    • ....
  • http status:
    • status:200
    • status:404
    • ....

User-defined tags

User-defined tags allow you to categorize k6 entities based on your own logic. The following entities can be tagged:

  • checks
  • thresholds
  • custom metrics
  • requests
import http from "k6/http";
import { Trend } from "k6/metrics";
import { check } from "k6";

let myTrend = new Trend("my_trend");

export default function() {
    // Add tag to request metric data
    let res = http.get("http://httpbin.org/", { tags: { my_tag: "I'm a tag" } });

    // Add tag to check
    check(res, { "status is 200": (r) => r.status === 200 }, { my_tag: "I'm a tag" });

    // Add tag to custom metric
    myTrend.add(res.timings.connecting, { my_tag: "I'm a tag" });

Tags in results output

{"type":"Point","data":{"time":"2017-05-09T14:34:45.239531499+02:00","value":459.865729,"tags":{"group":"::my group::json","method":"GET","status":"200","url":"https://httpbin.org/get"}},"metric":"http_req_duration"}

Read more about the k6 results output syntax (https://docs.k6.io/docs/results-output#section-json-output) to see how tags affect your test result output.

Tags and Groups