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

Annotations already cover safety (readOnlyHint, idempotentHint, destructiveHint false, openWorldHint false), so the bar is lower. The description still adds real value by disclosing the response contents — status, failure reason, health score, warmup, limits, signature — which matters because there is no output schema.

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 sentences, no filler, and the payload content is front-loaded before the optional-parameter note. Every clause earns its place.

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 read-only single-resource fetch with no output schema and no nested objects, enumerating returned fields plus the optional verification flag is sufficient. Only error behavior for an unknown id is unaddressed, a minor omission.

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 coverage is only 50%: 'id' is documented in the schema, but includeVerification has no schema description. The description compensates by explaining exactly what that flag adds (the latest SMTP/IMAP connection test result), so the parameter gap is closed.

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 fragment 'One mailbox: status, why it last failed, health score, warmup, limits, signature' makes clear this retrieves a single mailbox and enumerates what comes back. The singular framing implicitly distinguishes it from list_mailboxes, but no sibling is named outright, so an agent must infer the id-based lookup shape.

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-this vs list_mailboxes or update_mailbox guidance; the id-required schema implies lookup-by-id. The one conditional instruction — 'Set includeVerification to also get the latest SMTP/IMAP connection test result' — is genuine usage guidance for the optional parameter, which lifts it above a bare 2.

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