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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false), yet the description still adds substantial behavior: per-format return behavior (text/CSV/JSON/HTML/code, images, PDFs/Word extraction), the caveat 'when it extracted any,' and a hard 10 MB limit. This is meaningful context beyond structured fields.

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-loaded with the core action, then the return-format detail, then the size cap and ID source. Every sentence carries information the agent needs; no filler.

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?

There is no output schema, so the description correctly carries the burden of describing return values by file type, including the extraction caveat and size limit. The only incomplete piece is the messageId parameter, whose semantics are not addressed.

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 only 33% (mailbox documented; messageId and attachmentId bare), so the description must compensate. It does explain where attachmentId comes from (get_agentmail_message/get_agentmail_thread), but messageId is left entirely unexplained in both schema and description.

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 ('Open one attachment of an AgentMail message and return what is in it') and pins the scope to AgentMail, which separates it from the sibling read_gmail_attachment and read_outlook_attachment. The return-format breakdown further confirms what the tool does.

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 concrete workflow guidance: 'Get attachmentId from get_agentmail_message or get_agentmail_thread,' which tells the agent the prerequisite call. It does not, however, state when to prefer this over read_gmail_attachment/read_outlook_attachment or any exclusions, so no explicit when-not guidance.

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