Load Test Bootstrap

Load Test Bootstrap

Most NFR audits ask "is there a performance budget test?" and then move on without one existing. This skill actually builds and runs a small, bounded load test — the thing that would catch a database connection pool exhausting at 50 concurrent users, or a serverless function's cold-start tax showing up only under real concurrency, neither of which Lighthouse can ever find (it tests one page load, alone, once).

Works against any HTTP target: a static site's CDN edge, a backend API, a serverless function endpoint — k6 and Artillery are both just HTTP load generators underneath.

When not to use this

• Single-user page-load performance (LCP, TBT, bundle size) → Lighthouse / nfr-gap-audit's baseline, or production-cwv-review for real-world field data. This skill measures throughput and latency under concurrency, not single-load render performance.
• Production, without the user's explicit go-ahead on target and intensity — never assume authorization. Real load against a live site is not a read-only audit action; treat it with the same care as any other action with real external effect.
• A one-off "is the site up" check → that's a health check, not a load test; way overkill for the question being asked.

Phase 0 — Scope & consent (never skip)

Before writing or running anything, confirm explicitly with the user:

1. Target: which 2-5 endpoints (homepage, one form POST, one API route) — critical paths, not everything.
2. Environment: staging/preview URL strongly preferred; production only with explicit, informed agreement to a bounded intensity.
3. Intensity: a conservative default proposal — e.g. ramp 0→20 virtual users over 30s, hold 1 minute, ramp down over 15s — and let the user raise or lower it. Never default to an aggressive profile against a target you don't control the infrastructure cost of.
4. Timing: avoid peak traffic hours if testing production; ask if there's a known low-traffic window.

If the user hasn't given clear, specific answers to all four, stop and ask — this is the one phase in this skill (and arguably in this whole audit family) where proceeding on an assumption is a real-world mistake, not just a wasted review cycle.

Phase 1 — Scaffold

Write a k6 script (load-test.js, saved locally — not committed unless the user wants it kept as a repeatable asset) with:

• The agreed ramp profile (stages in k6's options)
• One scenario per agreed endpoint
• Thresholds that make the run pass/fail objectively: http_req_duration: ['p(95)<800'], http_req_failed: ['rate<0.01'] (adjust the numbers to the site's own stated performance targets if it has any, e.g. this project's Lighthouse total-blocking-time budget)

Artillery is a reasonable alternative if the project already uses it or the user prefers YAML config over k6's JS.

Phase 2 — Run

Execute against the agreed target at the agreed intensity.

• If k6/Artillery isn't installed locally, ask before installing (per the project's own "ask before installing tools" convention) — a Docker fallback (docker run --rm -i grafana/k6 run - <load-test.js) avoids a local install entirely if Docker is already available.
• Watch the run live if possible; abort immediately if error rates spike well beyond the threshold or the target shows signs of real distress (this is production-adjacent risk management, not just test hygiene).

Phase 3 — Findings

Report per endpoint: p50/p95/p99 latency, error rate, and — if the ramp was steep enough to find it — the approximate VU count where the target started degrading (rising error rate or latency knee). Compare against the thresholds set in Phase 1 and call out any that failed.

Do not extrapolate beyond what was actually run — "held up fine to 20 VUs over 1 minute" is the honest scope of the finding, not "the site can handle production traffic."