The body is lean and assumes Claude's competence; the overview is a single quoted line plus brief framing, and the time-sensitive version (3.27.7) is flagged with 'check Maven Central for the latest'. A few short restatements of API behavior keep it just within the 'every token earns its place' anchor.

Provides fully executable Java throughout — install snippets, assertThat chaining, collection/exception/soft/recursive/custom assertions, plus a complete example test method — all copy-paste ready.

Sequenced from Step 1 Install through Step 7 Custom assertions to a worked Example, Anti-patterns, and Limitations; no validation checkpoints are needed because the skill is explicitly a reference that 'does not run tests', so the destructive-ops cap does not apply.

SKILL.md stays an overview, offloading advanced per-feature variants to the verified, one-level-deep references/matcher-catalog.md with clearly signaled links at the end of each relevant step.

Enumerates many concrete actions including the assertThat entry point, collection matchers (contains, containsExactly, allSatisfy, extracting), exception assertions, SoftAssertions, recursive comparison, and custom assertions via AbstractAssert.

Explicitly answers what it does (full coverage list) and when to use it via a clear 'Use when writing JVM tests that need richer failure messages...' clause.

Includes natural user phrases such as 'writing JVM tests', 'richer failure messages than built-in assertEquals', and 'verifying complex object graphs, exception types, or collections', alongside the domain-specific API names.

Occupies a clear niche (AssertJ fluent assertions on the JVM) with triggers like 'richer failure messages than built-in assertEquals' that distinguish it from the junit5-tests/testng-tests/spock-test runner sister skills.