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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. The description adds the accepted identifier forms and the shape of the result (conversation plus counts), but says nothing about rate limits, paging behavior beyond counts, or truncation of large bodies. With annotations carrying the safety burden, this is adequate but thin.

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 core behavior is front-loaded ahead of the sibling routing. Every clause carries information.

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 re-explained, and the identifier ambiguity is handled. However, with 7 parameters at 0% schema coverage, an agent still cannot tell what new_only, full_body, body_max_chars, recipients_limit or attachments_limit do — a real gap for a tool with this many tuning knobs.

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 compensate and largely does not. It does explain the required 'identifier' parameter (stored id vs RFC822 Message-ID string), which usefully resolves the int|string anyOf, but limit, new_only, full_body, body_max_chars, recipients_limit and attachments_limit are left entirely undocumented.

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 conversation object) and names its scope (messages plus total/returned counts). It clearly separates itself from mail_show ('one stored message') and mail_search, so an agent can pick it without opening any schema.

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?

Explicitly routes the agent: use mail_search to obtain identifiers, and use mail_show when a single stored message suffices — implying this tool is for the whole thread. Alternatives and the conditions that select them are named rather than left to inference.

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