Lists multiple specific concrete actions: 'write a failing test first', 'implement the minimum code to make it pass', 'refactor while keeping tests green'. These clearly describe the red-green-refactor workflow steps.

Clearly answers both 'what' (guides the red-green-refactor TDD workflow with specific steps) and 'when' (explicit 'Use when...' clause with multiple trigger phrases and scenarios).

Excellent coverage of natural trigger terms: 'TDD', 'write tests first', 'red-green-refactor', 'test-driven development', 'failing tests before code', 'make the test pass', 'test coverage', 'unit tests before implementation'. These are terms users would naturally use.

TDD/red-green-refactor is a clearly distinct methodology niche. While 'test coverage' and 'unit tests' could overlap with general testing skills, the combination with TDD-specific terms like 'red-green-refactor' and 'failing tests before code' makes it highly distinctive.

The skill is mostly efficient with good executable examples, but includes some unnecessary guidance that Claude already knows (e.g., 'Understand the requirement — what specific behavior must exist?', 'Don't write a test when: Non-functional changes (formatting, comments)', common mistakes like 'Writing tests after code — defeats the design benefit of TDD'). The 'Common Mistakes to Avoid' and 'Decision Points' sections add moderate value but could be tighter.

Excellent executable examples throughout — the Jest code is copy-paste ready, shows the complete RED-GREEN-REFACTOR cycle with real code, and the end-to-end example demonstrates adding a new behavior with concrete, runnable code at each phase.

The workflow is clearly sequenced with explicit phases (RED → GREEN → REFACTOR), validation checkpoints ('Run the test — it MUST fail', 'Run tests after every change'), a verification checklist, and a feedback loop implicit in the cycle structure. The end-to-end example reinforces the sequence concretely.

The content is well-structured with clear sections and headers, but it's somewhat long for a single file with no bundle support. The 'Integration with Other Skills' section references other skills (test-patterns, anti-patterns, debugging/root-cause-analysis) but these aren't provided in the bundle, and the inline content could benefit from splitting the end-to-end example or decision points into separate reference files.