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K6 Test Maintenance

Grafana LabsOfficialPublished by Grafana Labs

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  • Software development
  • Apache-2.0
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From the author

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. Maintains existing scripts; to author a new test use the k6 skill, or k6-browser-test for a browser test.
— the description by Grafana Labs

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

The k6-test-maintenance skill provides a structured, safety-first approach to updating existing k6 performance tests. It covers five core maintenance tasks: threshold tightening, version migration, service change adaptation, code refactoring, and best-practices auditing. The skill enforces a strict behavior-aware change control process, distinguishing between syntactic changes (which can be applied automatically) and behavioral changes (which require user review and confirmation). It integrates with k6-manage and Grafana Cloud APIs to ensure that all modifications are validated through parse-checks and cloud-based smoke tests before being finalized.

What it does

  • Tightens threshold values based on historical trend data and metric observations.
  • Migrates scripts to newer k6 versions by identifying deprecated APIs and patterns.
  • Adapts existing test scripts to accommodate changes in the underlying service.
  • Refactors test code for improved cleanliness and adherence to current best practices.
  • Audits scripts against official k6 documentation to ensure optimal performance and reliability.
  • Validates all changes using a multi-stage process including parse-checks and cloud smoke runs.

When to use it

  • When a test is failing after a service deployment or infrastructure change.
  • When you need to update thresholds to reflect current performance trends.
  • When migrating legacy scripts to a newer k6 release.
  • When you want to refactor or modernize your existing test codebase.
  • When you need to ensure your scripts align with current k6 best practices.

Advantages

  • Reduces risk by classifying changes as syntactic or behavioral before application.
  • Prevents breaking CI gates or SLOs through rigorous verification recipes.
  • Grounds all recommendations in official k6 documentation and API references.
  • Provides a safe, standardized workflow for cloud-hosted script management.
  • Minimizes manual effort by automating syntactic refactoring and validation.

Usage examples

“My k6 test is failing after the latest service deployment, can you fix it?”
The agent will analyze the service changes, identify the impact on the test script, propose necessary adjustments, and guide you through the verification process.
“Tighten my p95 thresholds based on the last 30 days of data.”
The agent will query historical metrics, calculate appropriate new thresholds, present a pass/fail impact table, and apply the changes upon your approval.
“Migrate this script to k6 v2.”
The agent will identify deprecated APIs, propose the required syntax updates, and perform a cloud smoke test to ensure the migrated script functions correctly.
“Refactor my k6 test to follow best practices.”
The agent will audit the script for common issues, suggest cleaner patterns, and provide a diff for any behavioral changes before applying them.

Install

  1. Download the skill as a ZIP:

    https://autogineer.com/agent-skills/grafana/k6-test-maintenance/download
  2. Unzip it into the cross-client skills folder of your project:

    mkdir -p .agents/skills && unzip k6-test-maintenance.zip -d .agents/skills

Documentation by Grafana Labs

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:

  1. Threshold tightening -- adjust threshold values based on observed metrics

  2. Version migration -- update scripts for new k6 releases

  3. Service change adaptation -- fix tests when the underlying service changes

  4. Refactoring -- clean up and modernize test code

  5. 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:

  1. 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.

  2. Local smoke (non-browser, service reachable): k6 run --vus 1 --iterations 1 <script>.

  3. Classify the change (below) and verify per the matrix -- recipes in references/verification.md.

  4. 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
ClassTest durationVerification
Aanysha256 + k6 inspect + historical pass/fail prediction. No cloud run needed.
Bshort (< 5 min)sha256 + k6 inspect + full cloud run (k6-manage §11).
Blong (≥ 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:

  1. mcp-k6 (preferred): get_documentation("best_practices"), get_documentation("javascript-api/k6-browser"), validate_script(...).

  2. k6 x docs CLI (always available):

    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.

  3. 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.

Authoring a new test, not maintaining one? This skill improves scripts that already exist. To write a new browser test from a plain-language user journey (selectors discovered by exploring the live site), use the k6-browser-test skill; for other new k6 scripts, use the k6 skill.

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

IssueDetail
Cloud script formatGCk6 scripts can be single files or tar archives. Detect with file(1) before editing (see k6-manage §5).
Zero-observation thresholdsA threshold on a metric with no observations passes by default. When adding new thresholds, ensure the metric is actually emitted by the test.
abortOnFail cascadesIf a threshold has abortOnFail: true, tightening it means runs abort earlier. Warn the user.
Browser script validationBrowser 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 alignmentk6 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 editAfter 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

Files

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Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

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Attribution and licence

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grafana/skills · skills/grafana-k6/k6-test-maintenance · commit 8fb72a5
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Apache License 2.0 (redistribution allowed)
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