Conciseness

38 lines with zero padding: every bullet is skill-specific guidance (tool names, parameter semantics, confirmation requirements). No concept explanations Claude already knows, nothing trimmable without losing guidance. Not 4: there are no minor instances of over-explanation to trim.

Actionability

Instruction-only skill with fully concrete guidance: exact tool names (list_inboxes, get_inbox, create_inbox, update_inbox, delete_inbox), exact parameters (requested username, verified domain, display name, metadata, client ID), exact semantics ("metadata keys merge and that setting keys to null removes them"), and an explicit return contract. Absence of code is not penalized per the scoring note since the guidance is actionable.

Workflow Clarity

The destructive-operation cap does not apply because validation is explicit: "only after showing the exact inbox ID/address and receiving explicit confirmation" plus the invalidation rule ("Changed target/scope invalidates confirmation"). Each action has a complete precondition (create only after user request with verified domain; update with merge semantics; delete with exact-object preview and confirmation). Not 4: no validation checkpoints are missing.

Progressive Disclosure

Under 50 lines with well-organized sections (Workflow, Authorization, Guardrails) and one clearly signaled one-level reference to the sibling skill's references/threat-model.md for the full threat model. Per the simple-skill guideline, this earns a 5; the inline matrix rows are appropriately scoped as this skill's contract.

Specificity

"Create, list, inspect, update, or delete AgentMail inboxes through the connected MCP server" names five concrete lifecycle actions with comprehensive coverage of the domain. Not 4: there are no coverage gaps — every inbox lifecycle operation is enumerated, matching the comprehensive anchor.

Completeness

Explicitly answers both what ("Create, list, inspect, update, or delete AgentMail inboxes through the connected MCP server") and when ("Use for ANY inbox lifecycle request... Also use when the user asks for a new agent email address...") with concrete trigger phrases. Not 4: the when-clause is explicit and specific, not merely present.

Trigger Term Quality

Natural user phrasings are comprehensively covered: "a quick list-inboxes", "a simple delete", "a new agent email address", "wants inbox details changed", "removes an inbox", plus exclusion triggers like "sending mail" and "reading or triage". Not 4: synonyms and colloquial variations (inbox lifecycle, agent email address, removes an inbox) are all present.

Distinctiveness Conflict Risk

Clear niche with explicit negative scoping: "do not use for sending mail (agentmail-send-email), reading or triage (agentmail-check-email), or MCP connection setup (agentmail-mcp)" removes any conflict risk with sibling skills. Not 4: the do-not-use clauses make overlap risk minimal rather than minor.