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

Annotations already declare read-only/idempotent, so the description doesn't need to repeat that; instead it discloses the meaningful behavior: four possible states, the owner-approval gate, the 24-hour expiry that results in nothing being sent. That is exactly the context an agent needs beyond the safety hints.

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?

One tight sentence with the outcome enumerated in a parenthetical; front-loads the purpose before the state list. No filler, though the parenthetical is dense.

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 one required parameter, an output schema present, and annotations covering safety, the description completes the picture by explaining what each state means and the expiry rule. Only polling/terminal-state guidance 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?

Schema coverage is 100% and the single parameter is fully documented in the schema as the outgoing_message_id from send_message. The description adds no extra detail about the identifier, so baseline 3 applies.

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+resource ('whether an email prepared with send_message was sent') and ties it to the sibling that creates the item, so the agent can distinguish it from get_message or search_messages. It stops short of naming the alternative read-content tool explicitly.

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?

Implies the tool is used after send_message to poll for approval/send outcome, but gives no explicit when-to-use versus siblings or guidance on polling cadence or when the status is final.

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