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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered; the description adds value beyond that by disclosing the exact return payload (folder name, message count, unread count) and the cross-tool semantic dependency. It does not mention permissions or rate limits, keeping it out of the 5 band.

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 dense sentences with zero filler: the first defines scope and return values, the second defines how to use them. The most decision-relevant information (what is listed and its scope) is front-loaded.

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?

There is no output schema, so the description carries the burden of describing return values, and it does so precisely (name, message count, unread count). For a single-param read tool with covering annotations, nothing an agent needs in order to call it correctly 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 with 100% schema description coverage ('Full mailbox address'), so the schema already does the heavy lifting. The description's 'in one mailbox' reinforces the scope but adds no syntax, format, or example beyond the schema, which is the baseline expectation at full 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 every folder in one mailbox') with explicit scope, and enumerates the folder kinds covered (Inbox, Sent, Drafts, Trash, Junk, custom). It also differentiates from the similarly named list_mailboxes by anchoring to 'one mailbox' and naming the returned folder set.

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?

Gives a clear reason to call it: the returned names are 'the valid values for the folder and destination parameters of the other mail tools,' which tells the agent this is a discovery/prerequisite step. It stops short of naming a specific alternative tool or a when-not condition, so it falls just under the top band.

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