list_messages

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden. It usefully declares read-only semantics and that bodies are excluded, which sets return expectations, but says nothing about ordering, pagination behavior with the limit cap, permissions, or error conditions for invalid account/mailbox.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two short, front-loaded sentences with no filler; the core action leads and the scope caveat follows. Efficient, though the second sentence is brief enough that more could have been said without bloat.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description must set return expectations, and it does partially ('summaries', 'bodies not included'). However, for a 4-parameter listing tool it omits ordering, total-count/pagination behavior, and what a 'summary' contains, leaving gaps relative to what an agent may need.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so every parameter (account, mailbox, limit, unread_only) is already documented with defaults and bounds. The description adds no parameter-specific detail beyond implicitly confirming summary-level output, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource: 'List message summaries from an Apple Mail mailbox.' The word 'summaries' signals this is a lightweight listing, not full message retrieval. It does not name or contrast with siblings like search_messages or get_message, so it falls short of a 5.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is only implied: an agent can infer this is the browse/list entry point for a mailbox, versus get_message for full bodies or search_messages for queries. No explicit when-to-use or when-not-to-use guidance, and no alternatives are named.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.