Show one stored message

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description adds useful context that the body and collection fields are 'bounded', signalling truncation, though it does not state what the bounds are or how truncation is surfaced.

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. The primary action and identifier form are front-loaded, and the disambiguation guidance follows immediately.

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 return values need not be described, and the routing guidance is complete. The only residual gap is that the default bound values and truncation behavior of the limit parameters are not described anywhere in prose.

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 0%, so the description must carry the load. It clarifies that message_id is an integer stored id and implies bounding of body/collection fields (mapping to body_max_chars, recipients_limit, attachments_limit), but leaves new_only and the string form of message_id unexplained.

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?

States a specific verb and resource ('Return one stored message object by integer stored id') and explicitly names the scoping mechanism. It clearly separates itself from mail_search (id discovery) and mail_thread (RFC822 Message-ID / full conversation), so an agent can choose without opening schemas.

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?

Gives explicit routing rules: use mail_search to obtain valid ids, and use mail_thread when the identifier is an RFC822 Message-ID string or a full conversation is wanted. Both the when and the when-not alternative are named.

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