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

Annotations declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. Beyond that, the description discloses the payload contents (plan, limits, usage, domains, prefix, upgrade path) and the non-obvious rule that only addresses sharing your prefix can be restored. It stops short of stating auth requirements or pagination/format, but for a no-parameter read this is solid added value.

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 primary payload contents are front-loaded in the first sentence, with supplementary upgrade info trailing. The parenthetical about the address prefix is a mild interruption, and the second sentence is somewhat expendable, but nothing is redundant enough to hurt.

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 carries the return-value burden and does so reasonably, enumerating the main fields. Terms like 'current usage' and 'limits' remain imprecise (which metrics, what units), which is the main gap for a payload the agent must interpret.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; baseline is 4. No parameter-level detail is needed or missing.

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 names the resource (the account) and enumerates the specific content returned: plan, limits, current usage, available mail domains, address prefix, and upgrade availability. That is well beyond a tautology. It does not explicitly contrast itself with siblings like list_mailboxes, though the account-scoped content makes the distinction inferable.

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 statement of when to call this versus alternatives; usage is only implied by the content it returns. It does contain an actionable domain rule — the address prefix governs what can be restored — which points toward restore_mailbox, but that is context rather than call guidance.

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