The body is lean and code/table-driven with no padding explaining concepts Claude already knows; the Overview, anti-patterns table, and Limitations each earn their tokens, with only minor redundancy between the Overview and When-to-use runner list.

Provides fully executable, copy-paste-ready guidance: npm install, install/tick/tickAsync/setSystemTime code blocks, `npx mocha`/`npx vitest run`, and a CI yaml, plus a concrete anti-patterns table with explicit fixes.

For a simple single-purpose library skill, the Install → Basic install → Tick → Async tick → Teardown sequence is clear, and the critical 'leaked clocks contaminate subsequent tests' warning with `afterEach(() => clock.uninstall())` acts as the key validation checkpoint for the main risk.

SKILL.md is a concise overview that offloads advanced detail to a single clearly-signaled, one-level-deep link to references/advanced-scenarios.md (verified present); sibling/cross-language catalogs are listed by name without nesting.

Lists multiple concrete actions (install(), tick()/tickAsync(), setSystemTime(), restore(), toFake selective override) plus the surfaces it covers (setTimeout/setInterval/requestAnimationFrame, Date/performance.now()/hrtime), matching the 'lists multiple specific concrete actions' anchor.

Explicitly answers both what ('Wraps Sinon's standalone @sinonjs/fake-timers library... install(), tick() / tickAsync()...') and when via an explicit 'Use when JS/TS code needs deterministic timer or clock control and the test runner does not already expose this library...' clause.

Natural trigger terms a user would say are present ('fake timers', 'deterministic timer or clock control', runner names Mocha/AVA/Jasmine), giving good coverage; it is not merely technical jargon.

Niche is sharply bounded to Sinon's standalone fake-timers for runners lacking a built-in fake-timer API, making conflict with sibling skills (e.g. jest-fake-timers) unlikely.