Conciseness

The ~20-line body is lean and assumes competence: step 2's cause list ("shared mutable state, counters, missing awaits, ordering assumptions, N+1 queries, blocking work on the request path, unbounded caches, leaking listeners") is a dense checklist rather than explanation, and no basic concepts are re-taught, matching the every-token-earns-its-place anchor.

Actionability

Guidance is concrete and quantitative throughout ("N≥20 runs", "0 failures in ≥1,000 calls", "3,000 realistic requests", "deployed p95 ≤ max(2× base p95, base p95 + 100 ms)", "flat over a 30-minute session", "k6"), but the measurement mechanics — e.g., the command or harness used to run the N trials or observe memory flatness — are not given, leaving minor gaps versus the copy-paste-ready anchor at 5.

Workflow Clarity

The five-step procedure (measure → find cause → fix → prove → load-test constraint) has an explicit, quantitative validation stage in step 4 plus an Exit criteria checklist, so every checkpoint is present — exceeding the most-checkpoints-present anchor at 4 and matching the explicit-validation-with-checklist anchor at 5; the prove-it criteria inherently gate completion.

Progressive Disclosure

This is a single-purpose skill under 50 lines with well-organized sections (Procedure, Exit criteria) and no need for external references; no bundle files ship with the skill, and the `qa-performance-resilience` mention is a counterpart-skill pointer rather than a dangling reference, so the simple-skill exception for a 5 applies.

Specificity

The description names five concrete problem types ("performance regressions, slow endpoints, memory growth, flaky failures, and race conditions") plus a concrete method ("finding the nondeterministic or slow cause", "prove it statistically under soak") and an explicit prohibition on sleeps/retries, matching the comprehensive-coverage anchor rather than the minor-gaps anchor at 4.

Completeness

It explicitly answers both what ("Fix performance regressions... by finding the nondeterministic or slow cause... and prove it statistically under soak") and when ("Use when the tester reports FLAKY, intermittent 5xx, slow pages, or degradation over time") with concrete trigger phrases, exactly matching the 5 anchor; the 4 anchor would require a less explicit 'when' clause.

Trigger Term Quality

Trigger phrases "FLAKY, intermittent 5xx, slow pages, or degradation over time" are natural report language with some synonym coverage (flaky/intermittent, slow/degradation), but common variations like "timeouts", "memory leak", or "high CPU" are missing, fitting the good-coverage-with-few-missing anchor at 4 rather than the comprehensive-synonym anchor at 5.

Distinctiveness Conflict Risk

It occupies a clear niche (root-cause fixes with an anti-sleep/anti-retry discipline plus statistical soak proof) with distinct report-based triggers, so it is unlikely to fire for the wrong skill; there is no meaningful overlap with generic debugging or feature skills.