Lean body of tight code snippets with only genuinely niche context (the Sinon-vs-Jest API deltas); it assumes Claude's competence and avoids explaining what timers or Jest are, with version framing scoped to the modern-vs-legacy distinction rather than padded prose.

Every section ships complete, executable TypeScript test snippets (enable/advance, async variant, runAllTimers, runOnlyPendingTimers) that are copy-paste ready with concrete assertions, hitting the top anchor.

For a single-purpose skill, the sections form an unambiguous sequence (Enable -> Advance -> Async -> Run all -> Run pending -> Advanced) with an anti-patterns table and limitations; no destructive/batch operation requires an explicit validation checkpoint here.

Core usage stays inline while selective-faking/DST/fetch material is split into the verified one-level-deep references/advanced-scenarios.md, clearly signaled by a link; the References section catalogues sibling resources for easy navigation.

Lists multiple concrete actions — jest.useFakeTimers(), jest.setSystemTime(), jest.advanceTimersByTime(), jest.runAllTimers(), and jest.useRealTimers() — matching the anchor for enumerating specific capabilities rather than merely naming a domain.

Explicitly answers both what (wraps the listed modern fake-timer APIs) and when ("Use when testing JS/TS code in Jest where setTimeout / setInterval / Date / Date.now need deterministic control"), satisfying the explicit-trigger anchor.

Natural user-facing terms are well covered ("fake-timers", "Jest", "setTimeout / setInterval / Date / Date.now", "deterministic control"); these are exactly what a user would say when needing this skill, not just internal jargon.

A narrow Jest-specific fake-timer niche with distinctive triggers; unlikely to fire for non-Jest or non-timer tasks, so conflict risk is low.