Conciseness

The body is lean and assumes competence — no explanation of what STEP files are or how APIs work; sections carry real payload (tool syntax, CLI examples, flag list). Minor trimmable redundancy: the placeholder prohibition appears twice ("must not be replaced with placeholder boxes or simplified stand-ins" in the intro and "Do not generate placeholder geometry for the selected purchasable part" in workflow step 4) and the part-category list is repeated between the first and second paragraphs. This fits 'Efficient; minor instances ... that could be trimmed' (4) rather than the every-token-earns-its-place anchor (5).

Actionability

Fully executable, copy-paste-ready guidance: a concrete native tool call with realistic arguments (cad.step_parts({"query": "M3 socket head 12", "download": true, "limit": 5})), three real CLI invocations including an exact stable id (--id iso4762_socket_head_cap_screw_m3x12), the literal search endpoint https://api.step.parts/v1/parts, and a specific flag list (--origin, --tag, --out-dir, --all, --overwrite). The examples cover the common cases (query search, id fetch, faceted search), matching the top anchor.

Workflow Clarity

The six-step workflow has a clear sequence with explicit validation and feedback loops: step 3 retries aliases 'before treating an empty result as a miss', step 5 'Verify sha256 when the API record provides it', and an error-recovery fallback ('If no credible STEP/STP source exists, mark the CAD role unresolved or ask for the real 3D file instead of inventing geometry') plus boundary rules for where downloads land. This matches 'Clear sequence with explicit validation steps; feedback loops for error recovery'; it is not a destructive operation and the sha256 checkpoint is unconditional in the workflow, so neither cap at 3 applies.

Progressive Disclosure

Good structure with an appropriate split: endpoint/field bulk lives in the real one-level-deep reference (the body's 'Read references/step-parts-api.md for endpoint and field details' matches the actual file, and scripts/download_step_part.py exists as cited). Two minor gaps keep it below the top anchor: the reference pointer is a single trailing line rather than a clearly signaled navigation section, and the provenance note cites a bundled 'text-to-cad-LICENSE' file that is not present in the bundle — a dangling reference. Fits 'Good structure; most content is appropriately placed; references mostly clear; minor organization gaps'.

Specificity

The description names its domain precisely ("off-the-shelf STEP parts for screws, bearings, motors, servos, connectors, boards, rails") but never states the concrete actions the skill performs (e.g., searching/downloading the parts) — the capability is only implied through "needs ... STEP parts". It sits at the 'names domain and 1-2 concrete actions, but not comprehensive' anchor: more concrete than the generic 'Names the domain but actions are minimal' (score 2) because the part categories and 'before creating placeholder geometry' add substance, but below 'Lists several specific actions' (score 4) because no explicit skill actions are enumerated.

Completeness

The 'when' is explicit and strong: "Use when Replicator needs off-the-shelf STEP parts ... before creating placeholder geometry" — a clear 'Use when...' clause with concrete triggers, so it avoids the cap at 3. The 'what' is discernible (sourcing real STEP parts rather than placeholders) but entangled in the trigger clause rather than stated as an explicit capability statement (e.g., 'Searches and downloads STEP files'). This matches 'Has both what and when; when could be more explicit or specific' inverted — the when is excellent, the what could be more explicit — placing it above the weak-what anchor (3) and below the 'clearly and explicitly answers both' anchor (5).

Trigger Term Quality

Strong natural keyword coverage: "screws, bearings, motors, servos, connectors, boards, rails", "STEP parts", "CAD components", "purchasable" — terms a CAD user would naturally say, including the format name (STEP). A few natural variants are missing (e.g., fasteners, bolts, STP, specific model numbers like '608zz' that appear in the body), which keeps it just below the 'comprehensive coverage including synonyms and file extensions' anchor but clearly above 'some relevant keywords but missing common variations' since it lists seven distinct natural part-type terms.

Distinctiveness Conflict Risk

The description carves out a clear niche — sourcing purchasable CAD components as real STEP files instead of placeholder geometry — with distinct triggers ("screws, bearings, motors, servos, connectors, boards, rails") that would not collide with generic CAD-modeling or document skills. The 'off-the-shelf'/'purchasable' scoping explicitly separates it from parametric-modeling skills. This matches the 'Clear niche with distinct triggers; minimal conflict risk' anchor.