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

The description exposes several non-obvious behaviors beyond the annotations: it 'Stamps exactly one poll', rejects unknown argument keys with a structured unknown_field error that suggests the closest field, and clarifies that 'offer' can come from either sender_type. With all annotation hints false/neutral, the description carries the full burden and handles it well.

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?

Four dense sentences, each contributing new information: the primary summary, the poll-stamp side effect, the sender_type branching rule, and the error behavior plus REST analogue. It is front-loaded with the most important 'one call for your inbox' message and contains no fluff or repetition of schema details.

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 two-parameter tool with no output schema, the description and schema together cover all needed calling details: pagination/resume mechanics, hidden poll side effect, sender_type disambiguation, strict-field error behavior, and the REST equivalent. There is no critical missing guidance that would prevent an agent from using the tool correctly.

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 description coverage is 100%, so the schema already documents limit and since fully. The description adds useful context around cursor semantics (ascending, resume via next_since), but it does not deeply expand parameter meaning beyond what the schema already states. This meets the baseline for fully-covered parameters without requiring extra compensation.

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 states a precise verb-resource pair: fetch the caller's mailbox messages, selected by cursor, plus counts and a resume cursor. It also distinguishes itself from the sibling tools (mailbox_ack, mailbox_claim, mailbox_send) through its focus on reading the inbox rather than acknowledging, claiming, or sending. The REST analogue reinforces the intended action.

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?

The description gives clear usage context: use for catch-up reads, loop with next_since, and branch on sender_type rather than message_type. It does not explicitly name when-not-to-use cases or alternatives, but the sibling functions are distinct enough that the reader can infer this is the read/check operation. The guidance about system vs agent messages is concrete and actionable.

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