Mailbox status

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

Annotations already establish readOnlyHint=true and openWorldHint=false, so safety is covered. The description still adds real behavioral value by disclosing that it exposes the user's own identity (with a warning against self-sending) and whether sending is enabled, which are traits the annotations do not convey.

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?

It is a single dense sentence plus a short usage clause; the parenthetical earns its place by explaining why self-address matters. It is front-loaded with the returned data, though the opening parenthetical is slightly heavy to parse.

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?

An output schema exists, so the description need not re-document return formats, and it correctly focuses on what the tool is for and when to call it. For a zero-param status tool this is essentially complete, with only minor room to note alternatives.

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 per the baseline there is nothing for the description to disambiguate. No parameter guidance is needed and none is 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 enumerates the specific data returned (user's own address/name, local time, unread count, sending-enabled flag), which is far more than a tautology and lets an agent distinguish it from siblings like get_message or check_mail. It lacks an explicit verb phrasing and never names the tools it is not, but the content is concrete and unambiguous.

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?

"Call first when you need today's date or want to check the mailbox is reachable" gives clear triggering conditions and even an ordering directive. It stops short of naming alternatives or exclusion cases (e.g., when to prefer check_mail), so it does not reach the explicit when/when-not bar of a 5.

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