The description mentions some concrete actions like 'creates multiple sub-feature specs with full traceability' and 'produces specification documents capturing WHAT to build and WHY,' but the core capability description is somewhat vague — 'iteratively develop a feature idea into a well-formed specification through guided conversation with architectural analysis' is more process-oriented than listing specific concrete actions.

The description explicitly answers both 'what' (iteratively develops feature ideas into well-formed specifications, creates sub-feature specs for XL features, produces specification documents capturing WHAT and WHY) and 'when' (extensive list of trigger phrases and the general condition of wanting to develop a feature idea into a specification). The 'Use when' equivalent is the opening clause.

The description includes an extensive list of natural trigger phrases users would actually say, such as 'feature spec', 'spec this feature', 'help me spec', 'design this feature', 'I have an idea for a feature', 'let's flesh out this feature', 'resume spec', 'break down feature', and many more variations. This provides excellent coverage of how users would naturally phrase their requests.

The description carves out a clear niche around feature specification creation specifically, with distinct triggers like 'feature spec', 'arness code feature spec', and 'arn-code-feature-spec' that are highly specific. It also distinguishes itself from plan creation by noting specs 'feed into plan creation,' clarifying the boundary between this skill and planning skills.

This skill is extremely verbose at ~500+ lines with extensive conditional branching, repeated context-passing instructions, and detailed edge case handling that could be dramatically compressed. Many sections explain orchestration logic that Claude could infer from shorter instructions (e.g., the lengthy agent dispatch context formatting, the detailed draft update protocol, the false-negative follow-up patterns). The skill reads more like an engineering design document than concise operational instructions.

The skill provides concrete step-by-step workflows with specific file paths, agent names, and decision trees, which is good. However, it lacks executable code examples — there are no actual commands, scripts, or template snippets shown inline. Key actions reference external files (feature-spec-template.md, greenfield-loading.md, xl-decomposition.md, agent-invocation-guide.md, specialist-pre-check.md, ensure-config.md) that are not provided in the bundle, making it impossible to verify completeness. The regex pattern and keyword lists are concrete and actionable.

The multi-step workflow is clearly sequenced (Steps 0-5) with sub-steps, and includes some validation checkpoints (draft detection, greenfield loading verification, sketch manifest validation). However, the workflow is so complex with numerous conditional branches (greenfield vs standard, XL vs normal, UI vs no-UI, security-relevant vs not, sketch available vs not, draft exists vs not) that it becomes difficult to follow. Missing explicit validation steps for the final spec output — there's no 'validate the spec is complete before writing' checkpoint, and destructive operations like deleting the DRAFT file lack confirmation.

The skill references 6 external files (greenfield-loading.md, xl-decomposition.md, agent-invocation-guide.md, feature-spec-template.md, specialist-pre-check.md, ensure-config.md) which is good progressive disclosure in principle. However, none of these bundle files were provided for evaluation, and the main SKILL.md still contains enormous amounts of inline detail that could be offloaded — particularly the agent context formatting blocks, the draft update protocol, and the sketch detection logic. The references are one-level deep and clearly signaled, which is positive.