Conciseness

The body is lean and sectioned, with only minor trimmable material: the opening meta-narrative ("This skill is the reference that makes that loop produce tests worth keeping... consult them before and during the loop, not after") and restated known wisdom ("Tests verify behavior through public interfaces, not implementation details"). Not 5 because a few sentences explain concepts Claude already knows; not 2-3 because there is no padded section and most tokens carry non-obvious judgment (the anti-pattern "tells", the pre-agreed-seams rule).

Actionability

Concrete, executable guidance throughout: "write down the seams under test and confirm them with the user", a literal question to ask ("What's the public interface, and which seams should we test?"), a worked tautology example ("expect(add(a, b)).toBe(a + b)"), and an explicit tool invocation ("call the Skill tool with 'codebase-design'"). Not 5 because there is no inline example of a good test or a full red-green cycle — those are deferred to files that are not in the bundle, leaving minor gaps.

Workflow Clarity

The loop is clearly sequenced ("Red before green. Write the failing test first, then only enough code to pass it", "One slice at a time") with one explicit checkpoint ("No test is written at an unconfirmed seam"). Not 5 because the core TDD validation — run the test and confirm it fails for the expected reason before implementing — is implied rather than stated, and there is no recovery guidance for when the failing test unexpectedly passes; not 3 because sequence and checkpoints are mostly present with only minor gaps.

Progressive Disclosure

Sections are well organized and the two external references are clearly signaled and one level deep ("See [tests.md](tests.md) for examples and [mocking.md](mocking.md) for mocking guidelines"), but neither tests.md nor mocking.md exists in the bundle (no references/ directory), so the navigation chain is broken. Not 4 because references must resolve to real files; not 2 because the inline content is appropriately structured rather than bulk that belongs elsewhere.

Specificity

"TDD loop, one vertical slice at a time (red, green, refactor)" names the domain and the loop's concrete phases, but does not mention the skill's other coverage (test-quality criteria, seams, anti-patterns, loop rules). It sits at "names domain and 1-2 concrete actions, but not comprehensive" rather than 4, which requires several listed actions, and above 2 because the phases named are concrete rather than generic.

Completeness

Explicit what ("TDD loop, one vertical slice at a time (red, green, refactor)") and explicit when ("Trigger: test-first development, TDD."), so the missing-trigger cap at 3 does not apply. Not 5 because the when-clause is terse and lacks concrete scenario phrasing (e.g., "when the user asks to implement a feature test-first").

Trigger Term Quality

"Trigger: test-first development, TDD." includes both primary natural phrases a user would say. It falls short of 5's comprehensive synonym coverage (no "write tests first", "red-green", "unit-test first") but exceeds 3's "some relevant keywords but missing common variations" since both dominant terms are present.

Distinctiveness Conflict Risk

"test-first development, TDD" are unambiguous niche triggers with minimal conflict risk; the body even delegates refactoring to a separate skill, further reducing overlap. No neighboring anchor fits better — 4's "minor overlap risk with closely related skills" is not evidenced.