Conciseness

The body is dense, opinionated bullet guidance with no tutorial padding ('Sequence diagram: message order across actors, services, or objects'), but it is not fully lean: routing to `../node-link-and-diagram-layout/SKILL.md` is repeated five times (Overview, Core Workflow step 6, Stack Defaults, Reference Guide, Adjacent Skills), and mobile/workspace guidance recurs in Core Workflow step 10, Output Expectations, and Adjacent Skills. That repetition keeps it at 4 rather than 5; it is well above 3 because nothing explains concepts Claude already knows.

Actionability

Guidance is concrete for a decision skill: named tools per scenario ('prefer DBML... Mermaid ER, or PlantUML IE/ER'; 'React Flow for editable node-edge UIs, Cytoscape.js for graph analysis... ELK or Dagre for auto-layout') and specific output requirements ('route foreign keys in dedicated gutters or ports; never let connectors run underneath table boxes'). It falls short of 5 because some directives stay abstract — 'Define the normalized model contract before rendering: nodes, edges, compartments, ports...' lists fields but gives no example of the contract, and there is no worked selection example showing the rules applied.

Workflow Clarity

The Core Workflow is a coherent 10-step decision sequence from modeling job through audience, notation, format, renderer, model contract, and export/testing, with concrete sub-criteria at each step. Validation appears only as a planning item ('semantic validation, and visual regression where layout matters') rather than explicit checkpoints in the sequence, and there are no validate-then-proceed feedback loops, which keeps it below 5; the sequence is complete and well-ordered, clearly above the 3 anchor's implicit-checkpoint gap.

Progressive Disclosure

The body is a concise overview plus decision rules, with a Reference Guide that signals exactly when to open each of five real one-level-deep files ('Read `references/formats-and-interchange.md` before reading, writing, converting, or round-tripping diagram formats'); all five referenced files exist and contain no further nested references. Cross-links to adjacent skills are peers, not nested detail. This matches the clear-overview-with-well-signaled-references anchor.

Specificity

The description lists six concrete actions — 'Design, critique, read, write, render, and implement' — applied to a clearly named domain ('UML and UML-like software diagrams'), matching the comprehensive-coverage anchor. Not a 4 because no concrete action category for this domain is obviously missing; not below 5 because the verbs are specific rather than generic filler.

Completeness

Both halves are explicit: what ('Design, critique, read, write, render, and implement UML and UML-like software diagrams') and when ('Use when the user mentions UML, sequence diagrams, ... or interactive diagram editors and explorers') with concrete trigger phrases. This mirrors the 5-anchor example structure exactly; a 4 would require a weaker or less explicit 'when' clause.

Trigger Term Quality

Trigger coverage is exhaustive: 'UML, sequence diagrams, class diagrams, activity diagrams, state machines... ERDs, database schema diagrams, C4, BPMN, swimlanes, flowcharts... PlantUML, Mermaid, Graphviz DOT, D2, Structurizr, DBML, diagrams.net/draw.io, Kroki'. This includes diagram-type synonyms, format names, tool names, and vendor-specific spellings, matching the comprehensive-coverage anchor including synonyms.

Distinctiveness Conflict Risk

The niche is distinct — formal/UML-family diagramming with named notations and tools — but broad terms like 'network diagrams', 'flowcharts', and 'diagram-as-code' create minor overlap with general graph-visualization and node-link layout skills. Mostly distinct with minor overlap risk against closely related skills fits the 4 anchor better than 5, whose example stakes out a uniquely owned file type and trigger set.