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

Annotations already mark this as non-read-only, non-idempotent, and destructive; the description adds meaningful behavioral context by explaining that this enqueues work asynchronously and that an idempotencyKey must be reused on retry. It does not contradict the annotations and helps set agent expectations about delivery timing.

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 short sentences, with the core action front-loaded and the operational caveats placed immediately after. Every clause earns its place; no redundancy.

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 two-mode tool with a rich schema and an output schema, the description covers the core modes, async queue behavior, and retry semantics. It leaves sibling routing to other definitions, but an agent has enough to invoke it correctly given the extensive schema documentation.

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 100%, so the input schema already documents idempotencyKey, mailboxId, message, draftId, and revision. The description adds little beyond the term 'exact draft revision,' which maps to existing schema wording about the current server revision.

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 action and resource: it queues a new message or an exact stored draft revision. This clearly separates it from siblings like reply_email, forward_email, and save_draft, and the second sentence distinguishes queueing from delivery.

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?

The description gives useful retry guidance and warns that queue acceptance is not delivery, but it never explicitly says when to prefer this over reply_email, forward_email, or save_draft, nor names alternatives. Usage context is implied by the wording rather than stated as explicit when/when-not guidance.

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