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

Goes well beyond the readOnly/destructive annotations: it discloses the return shape per mime type (utf-8 text for text/csv/vcf/vcard, metadata + note for binaries with no base64 dump), the exact auth scope and connection types, that ChatGPT profiles and share tokens cannot call it, and the $0.10 cost. This is rich behavioral context an agent cannot get from annotations alone.

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?

Front-loads the core action and key input source, then layers return behavior, auth, and cost. Dense but every sentence carries information; the parenthetical cost/auth fragments are slightly cramped but not wasteful.

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 read-only attachment fetch with an output schema present, the description covers everything an agent needs: inputs and their origin, per-type return behavior, auth requirements, profile/token restrictions, and cost. Nothing material is missing.

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?

With 0% schema description coverage the description must compensate, and it does for three of four params: message_id and attachment_id (with their source) and 'optional account'. The 'email' parameter is never mentioned, and no format/syntax detail is added for any param, leaving a real gap.

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 (download/read) and resource (one Gmail attachment) with the exact lookup keys (message_id + attachment_id) and where to obtain them (read_gmail_message.attachments). An agent can distinguish this from read_gmail_message and search_gmail 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 states the prerequisite source of the IDs and the auth conditions required to call it (mail.read on API key / non-ChatGPT OAuth; ChatGPT profiles and share tokens cannot call). It gives clear context for when it is usable, but does not name an explicit alternative or a when-not-to-use case beyond auth gating.

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