k6-test-maintenance

Original：🇺🇸 English

Translated

Maintain and improve existing k6 test scripts. Covers threshold tightening based on trend data, version migration between k6 releases, auto-fixing tests when the underlying service changes, refactoring for cleanliness, and auditing scripts against current best practices from docs. Use when the user asks to fix a failing k6 test, tighten thresholds, migrate a script to a new k6 version, refactor a test, update a script after a service change, or improve a script with best practices. Trigger on phrases like "fix my k6 test", "tighten my thresholds", "migrate to k6 v2", "update my test script", "refactor this k6 test", "my test is failing after a deploy", "apply best practices to my script", "modernize my k6 test", or "the service changed and my test broke". Also trigger when another skill (k6-trend-analysis or k6-cloud-investigate-test) hands off with a recommendation to edit a script.

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Sourcegrafana/skills

Added on2026-08-12

NPX Install

npx skill4agent add grafana/skills k6-test-maintenance

SKILL.md Content

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k6 Test Maintenance

Maintain, fix, and improve existing k6 test scripts. Five maintenance tasks, each with a step-by-step procedure in

references/workflows.md

:

Threshold tightening -- adjust threshold values based on observed metrics
Version migration -- update scripts for new k6 releases
Service change adaptation -- fix tests when the underlying service changes
Refactoring -- clean up and modernize test code
Best practices audit -- check scripts against current k6 best practices

Core principle: behavior-aware change control

Classify every proposed change by whether it alters the test's runtime behavior:

Syntactic (behavior unchanged): the k6 runtime produces identical metrics, pass/fail results, and endpoints. Examples: rename a variable,
```
let
```
→
```
const
```
, remove unused imports, update comments, reformat. Apply directly.
Behavioral (behavior differs): anything affecting metrics, pass/fail, timing, request targets, or load shape. Examples: threshold value changes, adding
```
sleep()
```
, endpoint URL updates, check rewrites, scenario changes, new thresholds. Always present as a diff with rationale and require confirmation.

The threshold for "behavioral" is deliberately low. If in doubt, treat it as behavioral and ask -- a trivial-looking threshold change can cascade to CI gates, SLO calculations, and alerting.

Dependencies

k6-manage
-- fetch and edit GCk6-hosted scripts safely (§5: GET, backup, edit, validate, PUT, verify by sha256). Read it before touching any cloud-hosted script.
gcx
-- sole tool for Grafana Cloud API access.
mcp-k6 tools --
```
validate_script
```
and
```
get_documentation
```
. Check availability first; fall back to
```
k6 x docs
```
if absent.
k6 x docs
CLI -- documentation lookup when mcp-k6 isn't configured.
k6
CLI -- local validation (
```
k6 inspect
```
,
```
k6 run
```
).

Validation loop (every edit)

Every workflow produces a modified script. Never present or PUT an unvalidated script -- run this loop, fixing and re-running until it passes:

Parse-check:
```
k6 inspect <script>
```
-- catches syntax errors, invalid options, broken imports. Works on all types including browser tests (no browser needed). If mcp-k6 is available, also run
```
validate_script
```
.
Local smoke (non-browser, service reachable):
```
k6 run --vus 1 --iterations 1 <script>
```
.
Classify the change (below) and verify per the matrix -- recipes in
```
references/verification.md
```
.
Cloud-hosted scripts: apply via the k6-manage §5 safe-edit recipe (GET → backup → edit → validate → PUT as
```
application/octet-stream
```
→ sha256-verify).

Change classification

Class A -- declarative-config only. The diff is confined to
```
options.thresholds
```
or similar declarative fields that don't alter what the k6 runtime executes; the bytes inside
```
default function
```
, imported modules, and check predicates are byte-identical. Example:
```
p(95)<500
```
→
```
p(95)<420
```
.
Class B -- runtime logic changes. Any change to
```
default function
```
, imports, helper modules, request URLs, check predicates, or to
```
scenarios.*.vus
```
/
```
iterations
```
/
```
duration
```
/
```
executor
```
(which alter load shape and metric distributions). Example: changing a URL, adding a check, rewriting auth, switching executors.

When in doubt, treat as Class B.

Verification matrix

Class	Test duration	Verification
A	any	sha256 + `k6 inspect` + historical pass/fail prediction. No cloud run needed.
B	short (< 5 min)	sha256 + `k6 inspect` + full cloud run (k6-manage §11).
B	long (≥ 5 min)	sha256 + `k6 inspect` + local 1-iteration smoke + `k6 cloud run` of a local copy with `--vus 1 --iterations 1` . PUT to the saved test only after the cloud smoke passes.

Verification depth depends on the change class, not the test's duration -- most edits don't need a full run, and production tests may run for hours. Per-class recipes (Class A prediction table, Class B short/long, edge cases like scenario changes and loosening) are in

references/verification.md

.

Documentation lookup

Before proposing any change that touches k6 APIs, imports, or patterns, confirm it against current docs and cite the source in your report -- this grounds recommendations in the real API, not stale model knowledge. Look up in order:

mcp-k6 (preferred):

get_documentation("best_practices")

,

get_documentation("javascript-api/k6-browser")

,

validate_script(...)

.

k6 x docs
CLI (always available):
bash
```
k6 x docs using-k6 thresholds
k6 x docs javascript-api k6-http
k6 x docs search "websocket migration"
```
2-call strategy: try the direct path first; if it returns a topic list, pick the subtopic and call again. Full parent paths required (
```
using-k6 thresholds
```
, not
```
thresholds
```
).
```
k6 x docs
```
serves docs for the installed k6 version -- it may lag the target version when migrating.
Web fetch (last resort):
```
https://grafana.com/docs/k6/latest/
```
.

Async check pattern

A common browser-test bug: using

check()

from

k6

with async predicates. The built-in

check()

does not await Promises, so

check(page, { 'title': p => p.locator('h1').textContent() === 'Foo' })

silently passes because the Promise object is truthy. Two valid fixes:

Async-aware check from jslib:

import { check } from 'https://jslib.k6.io/k6-utils/1.5.0/index.js'

-- then predicates can be

async

and

await

inside them works.

Resolve the value before the check:

const text = await page.locator('h1').textContent(); check(text, { ... })

-- keeps the standard sync

check

from

k6

.

When you hit this during any workflow (migration, refactor, audit), flag it as a behavioral bug and propose one of these fixes.

Script sources

GCk6-hosted -- fetched and pushed via
```
k6-manage
```
§5 (GET → backup → edit → validate → PUT → verify sha256).
Local on disk -- read and edit directly. Validate before presenting.

Determine the source before starting: a GCk6 test URL or ID is cloud-hosted; a file path is local.

Workflows

Full procedures are in

references/workflows.md

:

Threshold tightening -- propose values with observed-metric justification, diff, apply, Class A verify.
Version migration -- find deprecated/renamed APIs, classify syntactic vs behavioral, apply, Class B verify.
Service change adaptation -- map each service change to a script change, propose fixes, Class B verify.
Refactoring -- find issues, auto-apply syntactic, propose behavioral, Class B verify after confirmation.
Best practices audit -- doc-driven audit across thresholds, load design, resource management, code quality, and browser specifics.

All five follow behavior-aware change control: auto-apply syntactic changes, present behavioral ones as diffs for confirmation.

Gotchas

Issue	Detail
Cloud script format	GCk6 scripts can be single files or tar archives. Detect with `file(1)` before editing (see k6-manage §5).
Zero-observation thresholds	A threshold on a metric with no observations passes by default. When adding new thresholds, ensure the metric is actually emitted by the test.
abortOnFail cascades	If a threshold has `abortOnFail: true` , tightening it means runs abort earlier. Warn the user.
Browser script validation	Browser scripts can't be validated with `k6 run --iterations 1` without a browser. Use `k6 inspect` for parse-only validation, or `validate_script` via mcp-k6.
k6 x docs version alignment	`k6 x docs` serves docs for the installed k6 version; when migrating to a newer version, local docs may not reflect the target API. Note this in migration lookups.
Script drift after edit	After pushing a cloud-hosted script, the next run uses the new version, but historical runs keep their bundled snapshot. To investigate a past failure, compare the run-bundled script (read-only), not the current one.

References

```
references/workflows.md
```
-- step-by-step procedures for the five maintenance tasks
```
references/verification.md
```
-- per-class post-edit verification recipes