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

Goes well beyond the annotations: it discloses that an uncertain SMTP attempt is never automatically resent, that the return is a queued operation and not confirmation of provider completion, and how to confirm status. This is exactly the kind of async/at-most-once behavior an agent must know before calling a destructive, non-idempotent send.

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?

Six short sentences, front-loaded with the core action and the retry contract before the polling instruction. No filler; every sentence carries a distinct operational rule.

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?

With no output schema, the description correctly explains the immediate return value (a queued operation) and the next step (get_mail_action). Combined with annotations covering the safety profile, the definition is nearly complete; the remaining gap is the undocumented non-operationId parameters.

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 14%, so the description carries most of the burden, yet it only elaborates on operationId (idempotency-key semantics). accountId, messageId, replyAll, textBody, htmlBody, and senderIdentityId are left undocumented in both schema and description. The operationId guidance is valuable but insufficient to fully compensate for the coverage 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 and resource ("Reply to a message") that an agent can distinguish from send_email and forward_email by intent. It also reveals the operation is queued/asynchronous, which shapes expectations. It does not explicitly contrast itself with named siblings, keeping it just short of a 5.

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 when-to-use rules: supply a stable operationId and reuse it only for retries of this exact reply, never retry an uncertain send with a new operationId. It also routes the agent to the follow-up tool ("Poll get_mail_action with the returned operationId"), providing clear alternatives for checking status.

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