Conciseness

The ~25-line body is lean throughout: "A prototype is throwaway code that answers a question. The question decides the shape." sets scope in two sentences, and every rule carries a real constraint (e.g., a scratch DB "with a clear 'PROTOTYPE: wipe me' name") with zero padding or explanation of concepts Claude already knows. Nothing could be cut without losing guidance.

Actionability

Guidance is concrete for an instruction-only skill: "a tiny interactive terminal app that pushes the state machine through cases", "several radically different UI variations on a single route, switchable via a URL search param and a floating bottom bar", and "the repo's Bun script or a direct `bun <path>` command". It stops short of 5 because the actual build instructions are delegated to LOGIC.md and UI.md, which are not present in the bundle, and no runnable example is given inline.

Workflow Clarity

The sequence is clear: identify the question, pick a branch (with an explicit ambiguity fallback — "default to whichever branch better matches the surrounding code... and state the assumption"), apply the six rules, then "Delete or absorb when done" and capture the answer. "Surface the state... after every action" is a genuine feedback checkpoint. It misses 5 only because deciding whether the prototype actually answered its question is left to judgment rather than an explicit checkpoint.

Progressive Disclosure

The structure itself is well designed — a two-branch decision table pointing one level deep to [LOGIC.md](LOGIC.md) and [UI.md](UI.md), clearly signaled — but neither file (nor any references/, scripts/, or assets/ directory) exists in the bundle, so the navigation chain is broken. Not the 4 anchor's 'minor organization gaps': the branch detail the body defers to is simply absent.

Specificity

"Build a throwaway prototype to answer a focused logic, state-model, or UI question" names several concrete activity types (logic/state-model prototypes, UI mock-ups) with a clear deliverable and purpose ("before committing to production design"). It falls just below the 5 anchor because there is essentially one verb (build) rather than multiple distinct actions like extract/fill/merge.

Completeness

Both parts are explicit: the 'what' ("Build a throwaway prototype to answer a focused logic, state-model, or UI question before committing to production design") and a full 'Use when' clause listing five concrete trigger phrases. This matches the 5 anchor's what-and-when-with-concrete-triggers pattern.

Trigger Term Quality

"Use when the user asks to prototype, sanity-check a model, mock up UI, explore design options, or try a few designs" covers natural synonyms comprehensively — 'prototype', 'sanity-check', 'mock up', 'explore design options', 'try a few designs' are all phrases a user would naturally say. No common variation is obviously missing.

Distinctiveness Conflict Risk

The throwaway-prototype niche with a clear pre-production-design framing is mostly distinct, but triggers like "mock up UI" and "explore design options" have minor overlap risk with closely related UI-generation or design skills. Not the 5 anchor's 'minimal conflict risk', but well above the generic overlap of 3.