Conciseness

The body is lean and every operational token (command name, args shape, tool name, skipCheck) earns its place. It is not a 5 because step 1 explains the publisher.extensionName ID format with an example — a concept Claude already knows — which is a minor instance of over-explanation, matching 'Efficient; minor instances of over-explanation that could be trimmed'.

Actionability

Guidance is highly concrete: the exact VS Code command 'workbench.extensions.installExtension', the args array format, and the exact tool 'copilot_runVscodeCommand' with 'skipCheck' set to true. It falls short of fully executable (5) only because the args include the placeholder 'installPreReleaseVersion: boolean' rather than a concrete value, leaving a small gap the reader must resolve — matching 'Mostly executable guidance; concrete code or commands with minor gaps'.

Workflow Clarity

This is a simple, single-purpose skill and the sequence is unambiguous: identify the extension ID, construct the command args, execute via the named tool. The one decision point (pre-release vs. stable) is explicitly resolved by the NOTE with clear conditions, and the operation is non-destructive, so the simple-skill exception applies and no validation checkpoint is required.

Progressive Disclosure

The skill is under 50 lines, self-contained, and needs no external references — no bundle files exist to split content into. Per the rubric's guideline for such skills, a short, well-organized body (numbered steps plus a clearly signaled NOTE) earns full marks with nothing inlined that belongs in a separate file.

Specificity

The description names the domain and one concrete action — "install a VS Code extension from an extension ID" — but stops there, offering no coverage of related capabilities (e.g., pre-release vs. stable selection, verifying installation, marketplace lookup). This matches 'Names domain and 1-2 concrete actions, but not comprehensive'; it is not a 4 because the surrounding phrase 'add new capabilities to their VS Code environment' is generic padding rather than additional specific actions.

Completeness

Both parts are explicitly present: the 'what' is clear ('install a VS Code extension from an extension ID') and the 'when' is stated ('Useful when the user wants to add new capabilities to their VS Code environment by installing extensions'). It falls short of a 5 because the 'when' clause largely restates the 'what' instead of giving concrete trigger situations, fitting 'Has both what and when; when could be more explicit or specific'.

Trigger Term Quality

Natural user phrases are present — 'install a VS Code extension', 'installing extensions', 'extension ID' — which a user would plausibly say verbatim. It is not a 5 because common variations like 'add an extension', 'marketplace', or '.vsix' are missing, and not a 3 because the core vocabulary users actually use ('VS Code', 'install', 'extension') is well covered.

Distinctiveness Conflict Risk

The niche is fairly distinct — installing VS Code extensions specifically from an extension ID — with minimal overlap risk against unrelated skills. It is not a 5 because the trigger phrase 'add new capabilities to their VS Code environment' is broad enough to potentially overlap with other VS Code configuration or setup skills, matching 'Mostly distinct; minor overlap risk'.