Conciseness

Nearly every line carries non-derivable repo knowledge — file paths, interface names, fixture IDs, exact mock methods, CI gate labels — with no explanations of concepts Claude already knows and no padding. This matches anchor 5 ('lean and efficient; assumes Claude's competence; every token earns its place') rather than 4, which would require identifiable over-explanation to trim.

Actionability

Guidance is fully executable and copy-paste ready: runnable commands ('./scripts/test.sh --grep "applyStorageSourceFilter|customizationCounts"', 'pnpm run typecheck-client'), complete code blocks for adding a tab fixture and for @playwright/cli eval diagnostics, and exact mock method names per customization type. It matches anchor 5's 'copy-paste ready code or commands; specific examples cover the common cases'.

Workflow Clarity

The main workflows are clearly sequenced with most checkpoints present: the five-layer sync table for API changes with 'verify both core and sessions registrations compile', CI regression gates that 'fail the CI status check' on screenshot changes, and a symptom/root-cause/fix table with error-recovery guidance for layout debugging. It falls short of anchor 5 because the add-fixture workflow has no explicit validate-rendered-output step, and the debugging loop's fix-then-recheck cycle is implied by the table rather than an explicit feedback loop.

Progressive Disclosure

No bundle files exist, so this is a single-file skill; external pointers (the spec at 'src/vs/sessions/AI_CUSTOMIZATIONS.md', '.github/instructions/ai-customization.instructions.md', and the 'component-fixtures'/'sessions'/'launch' skills) are clearly signaled with purpose and are one level deep. This matches anchor 4 ('good structure; most content is appropriately placed; minor organization gaps') rather than 5 because the 11-row fixture-ID table and the detailed mock-service requirements are inline content that could plausibly live in a reference file.

Specificity

The description names the exact target ('the Chat Customizations editor') and enumerates all seven managed item types ('agents, skills, instructions, hooks, prompts, MCP servers, and plugins'), giving concrete scope, but the only action is the generic 'working on' — no concrete verbs like edit, add, or debug. It sits between anchor 2 (generic actions) and anchor 3, earning 3 because the thorough item enumeration supplies concrete grounding the anchor-2 example lacks.

Completeness

Both parts are present: an explicit trigger clause ('Use when working on the Chat Customizations editor') and a 'what' ('the management UI for agents, skills, instructions, hooks, prompts, MCP servers, and plugins'). It matches anchor 4 rather than 5 because the 'what' identifies the artifact being worked on rather than explicitly stating what the skill itself provides (navigation, interfaces, testing guidance).

Trigger Term Quality

It includes natural terms users would say when working in this area ('Chat Customizations editor', 'agents', 'skills', 'hooks', 'prompts', 'MCP servers', 'plugins'), matching anchor 4's 'good keyword coverage; a few natural terms missing'. It is not a 5 because synonyms for the editor itself (e.g., 'customizations pane', 'manage customizations', 'Open Customizations') are absent.

Distinctiveness Conflict Risk

The trigger is scoped to a specific named editor with a clear niche, but the enumerated generic nouns ('skills', 'hooks', 'prompts') create minor overlap risk with skills about those items individually — anchor 4 ('mostly distinct; minor overlap risk') rather than 5.