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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is fully covered. The description adds that counts are returned and explains the semantics of the output fields, but since a full output schema exists, much of that is restating structured data rather than new behavioral context. The special_use explanation (locale-independent Sent/Trash/Drafts/Junk/Archive identification) is the one genuinely additive point.

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?

Three short sentences, front-loaded with the primary action, and every clause carries information. Light redundancy with the output schema keeps it from being maximally tight.

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 annotations, a single fully documented parameter, and an output schema, the description supplies what remains: the scope (one mailbox), the returned counts, and how to interpret path/name/special_use. Nothing essential for a correct call is missing.

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?

Only one parameter, and the schema documents it at 100% coverage ('Id from list_mail_accounts'). The description adds nothing about account_id and instead describes output fields, so it neither compensates nor detracts. Baseline 3 for full schema coverage.

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 and resource (list the folders) plus the scope (one mailbox) and the payload (message and unread counts). It is clearly distinguishable from every sibling, none of which list folders, though it never says so explicitly.

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?

There is no explicit when-to-use or when-not-to-use statement, but the clause '"path" is what the other tools take' implicitly tells the agent this is the discovery step that feeds move_message, create_folder, and similar tools. That hint is useful but left for the agent to infer.

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