Conciseness

The body is lean and purely prescriptive — "Execute one complete TDD cycle per requirement. Never test private internals." — with zero space spent explaining what TDD, mocking, or KISS/DRY are. Every section adds rules Claude does not already know (e.g., "Shameless Green is acceptable for a single new test"), matching the 5 anchor; the only near-redundancy (two overlapping UI-query bullets) is too minor to drop it to the 4 anchor.

Actionability

For an instruction-only skill the guidance is fully executable: each phase has an Input, numbered steps, and explicit present-items, including a copy-paste-ready literal ("The behavioral test `<test name>` still passes.") and concrete selector commands ("Prefer `getByRole` with accessible name"), with examples delegated to references/tests.md. This matches the 5 anchor's specificity and coverage; the 4 anchor would require missing key execution details, which are absent.

Workflow Clarity

The RED→GREEN→REFACTOR sequence is explicit with inputs, outputs, and validation checkpoints ("Confirmation that the test now passes, or the exact blocker if it cannot be run", the stop-gate "Stop after RED and wait for confirmation", and a Constraints checklist). It falls short of the 5 anchor because there is no error-recovery loop — e.g., what to do when the refactor breaks the test — only blocker reporting, which fits the 4 anchor (clear sequence, most checkpoints, minor gaps).

Progressive Disclosure

Clear overview sections with two well-signaled, contextual, one-level-deep references — "Read `references/mocking.md` when dependency boundaries or mocks are involved" and "Read `references/tests.md` for examples and red flags" — both verified to exist as real, substantive files (65 and 58 lines), with no nesting. This matches the 5 anchor exactly; the 4 anchor would require buried references or inline content that belongs in a separate file, which is not the case.

Specificity

Names several concrete actions — "Execute a strict Red-Green-Refactor TDD cycle for one requirement at a time while applying KISS and DRY" plus "Works for unit, integration, UI component, API, and CLI tests across stacks" — but the core action is one process plus principles rather than the multiple distinct actions of the 5 anchor (e.g., extract, fill, merge, convert). Fits the 4 anchor (several specific actions, minor gaps) better than 3, since it goes well beyond naming the domain with 1-2 generic actions.

Completeness

Explicitly answers both: the what is "Execute a strict Red-Green-Refactor TDD cycle for one requirement at a time while applying KISS and DRY" and the when is "Use when the user provides a business rule, acceptance criterion, bug fix, or feature requirement and wants test-first development..." — concrete trigger phrases for both, matching the 5 anchor exactly. Clearly above the 4 anchor, where the when would be less specific.

Trigger Term Quality

Comprehensive natural terms with synonyms: "test-first development, behavioral tests, failing tests first, TDD, red-green-refactor" alongside "business rule, acceptance criterion, bug fix, or feature requirement" — all phrases a user would naturally say when needing this skill. Not the 4 anchor because no common variation of the trigger vocabulary is missing; file extensions are inapplicable to a process skill.

Distinctiveness Conflict Risk

TDD with strict red-green-refactor triggers is a clear niche with mostly distinct triggers, but "bug fix" and "high-quality code" are broad enough to fire on ordinary bug-fix or code-quality requests where the user did not ask for test-first development — minor overlap risk with closely related coding skills, matching the 4 anchor rather than the minimal-conflict 5 anchor.