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

Annotations already declare readOnly, idempotent, non-destructive, and openWorld, so the safety profile is covered. The description still adds real value beyond them: accepted authentication methods (Bearer header or key argument), the scope requirement, and an explicit disclosure that no mail secrets are returned plus a warning that clients may retain key arguments in history.

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?

The purpose statement is front-loaded and dense, which is good, but the key-retention warning is repeated almost verbatim in both the description and the schema's parameter text, costing a third of the description with no new information. The result is serviceable but padded.

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?

For a single-optional-parameter read-only status tool with no output schema, the description covers the authentication model, the scope requirement, and the categories of information returned. The remaining gap is sibling disambiguation against mail_info and mail_credentials, which is not addressed at all.

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?

There is a single optional parameter with 100% schema description coverage, and the description's note about the key argument largely restates the schema's own text. The added value is naming the alternative (Authorization: Bearer header) as a substitute for the argument, but no format or precedence rules are given.

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?

The description uses a specific verb ('Check') and resource ('your mailbox') and enumerates the facets returned: address/status, eligibility, capacity, limits, and connection details. It also carves out a boundary ('no mail secrets'), though it never distinguishes itself from the sibling mail_info, which an agent would likely confuse it with.

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?

It states the prerequisite ('Requires account scope') and implicitly tells the agent this is a read-only inspection call, but gives no when-to-use guidance relative to mail_info, mail_credentials, or mail_enable/mail_disable. The agent must infer which mailbox tool to pick from the sibling list.

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