Conciseness

The body is overwhelmingly directive — 'Never modify the spec to make a failing verification pass', 'Run `quint typecheck` and fix all reported errors' — with no concept explanations Claude already knows. However, the 38-line ASCII workflow diagram duplicates the detailed Phase 0–4 sections that follow, and the compaction/compact-context advice ('Catalog the codebase compactly', 'Target: under 300 lines', the status block) recurs across three sections. This is 'minor instances that could be trimmed' (4), not fully lean (5) but well above noticeably verbose (2–3).

Actionability

Highly concrete: exact commands ('quint typecheck', 'quint run', 'quint verify', '--max-samples 5000'), a copy-paste plan-format template, a research prompt template, a compaction status template, and a tool-usage table. The gap that keeps it at 4 rather than 5 is that the pivotal gate syntax is never shown — how to select an invariant or witness in `quint run` (e.g. the actual flag) is implied ('with witness as invariant', 'with those invariants') but not executable as written, and 'quint REPL session + quint REPL eval' is not a verifiable command form.

Workflow Clarity

Exemplary sequencing: Phases 0–4 with a verification gate after every implementation step, rollback criteria in the plan template, explicit feedback loops ('If the gate fails: stop, diagnose, return to Phase 2', 'If invariant `[name]` fails after Step N, stop and return to planning'), a spec-change protocol requiring user approval, and failure-mode guidance for both violated invariants and unreachable witnesses. This matches the 5 anchor (explicit validation, error-recovery loops, checklist-style anti-pattern table).

Progressive Disclosure

No bundle files exist (no references/, scripts/, or assets/), and the skill is a self-contained ~260-line workflow with well-organized, consistently headed sections; nothing is buried or nested. It stays at 4 rather than 5 because the single file carries material that could be split — the detailed per-phase bodies restate the overview diagram, and the tool-usage/spec-change detail could live in one-level-deep reference files to keep SKILL.md a leaner overview. This is 'good structure with minor organization gaps', not the ideal overview-plus-signaled-references split of 5.

Specificity

Names the domain and several concrete actions — 'refactor code', 'add a new feature', 'close a gap between implementation and spec' — anchored by 'Implement code against an existing Quint specification'. Not comprehensive: the spec-change protocol and verification-gate capabilities that dominate the skill body are absent, which is the 'minor gaps' of the 4 anchor rather than the full coverage of 5.

Completeness

Explicitly answers both: what — 'Implement code against an existing Quint specification. Uses Research → Plan → Implement workflow (ACE-FCA style) grounded by the spec as the source of truth' — and when — 'Use when the user wants to refactor code, add a new feature, or close a gap between implementation and spec'. Both are present, explicit, and use concrete trigger phrases, matching the 5 anchor exactly; the 4 anchor requires a 'when' that could be more specific, which is not the case here.

Trigger Term Quality

Good natural phrases users would say: 'refactor code', 'add a new feature', 'close a gap between implementation and spec', 'Quint spec'. A few common variations are missing — e.g. the '.qnt' file extension (used only in the body) and phrasings like 'implement the spec' or 'make the code match the spec' — so it fits the 4 anchor ('a few natural terms missing') rather than the comprehensive synonym/extension coverage of 5.

Distinctiveness Conflict Risk

A clear niche — Quint-spec-driven implementation — with distinct triggers ('existing Quint specification', spec/implementation gap). It is clearly separable from generic refactor/coding skills, and the 'existing' qualifier distinguishes it from a spec-creation companion skill. Minimal conflict risk, matching the 5 anchor; it is well above the 'minor overlap risk with closely related skills' of the 4 anchor.