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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

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 easy visualization. Each execution of the supplied group() function also emits a group_duration metric that contains the total time it took to execute that group function. This, combined with the metric tags described below, enables very flexible performance monitoring of different groups in your test suite.

Tags

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 the following tags by default:

TagDescription
protothe used protocol name (e.g. HTTP/1.1)
subprotothe subprotocol name (used by websockets)
statusthe HTTP status code (e.g. 200, 404, etc.)
methodthe HTTP method name (e.g. GET, POST, etc.)
urlthe HTTP request URL
namethe HTTP request name
groupthe full group path
checkthe Check name
errora string with a non-HTTP error message (e.g. network or DNS error)
error_codeadded in k6 v0.24.0, this is a number that is unique for different error types; a list of current error codes can be found at the Error Codes page
tls_versionthe TLS version
scenariothe name of the scenario where the metric was emitted

If you choose, you could disable some of the above tags by using the systemTags option, just keep in mind that some data collectors (e.g. cloud) may require that certain tags be present. Also, you can enable some additional system tags, if you need them:

TagDescription
vuthe ID of the virtual user that executed the request
iterthe iteration number
ipThe IP address of the remote server
ocsp_statusthe Online Certificate Status Protocol (OCSP) HTTPS status

User-defined tags

User-defined tags allow you to categorize k6 entities based on your 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" });
}

Test wide tags

Besides attaching tags on requests, checks and custom metrics you can set test wide tags that will be set across all metrics. You can either set the tags on the CLI using one or more --tag NAME=VALUE flags or in the script:

export let options = {
  tags: {
    name: 'value',
  },
};

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 "
}
{
  "type ": "Point ",
  "data ": {
    "time ": "2017-05-09T14:34:45.625742514+02:00 ",
    "value ": 5,
    "tags ": null
  },
  "metric ": "vus "
}

Read more about the k6 results output syntax to see how tags affect your test result output.

Tags and Groups in k6 Cloud Results

In k6 Cloud Results you can see groups in the result tabs.

When using Groups, Checks and HTTP Requests can be viewed by group, as shown below. You can switch between the group and list layout by changing the "view as" selection in the top right.

k6 Cloud URL Grouping

Additionally you can filter the results by tags in the analysis tab.