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

The description discloses important behaviors beyond the annotations: email is irreversible ("cannot be recalled"), the account is shared across all callers, and the sending address may not be the one the agent created. These warnings add real operational risk context that the annotations' destructiveHint=true only hints at.

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?

The description is compact and front-loaded: it states the action and returns first, then the critical irreversible-send warning, then the shared-account caveat, and finally the sibling routing. Every sentence carries essential information with no filler or restating of schema.

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 high-stakes 12-parameter send tool, the description covers the operational essentials: the irreversible side effect, account context, prerequisite check (get_agentmail_inbox), and how to route to reply/draft instead. An output schema exists, so return values are already structured; the description supplements it with the usage-level context an agent needs.

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 fully describes all 12 parameters. The description briefly lists the main fields (to, cc, bcc, subject, text, html, labels, attachments) but adds no semantic detail beyond what the schema already provides. Baseline 3 is appropriate.

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?

Description opens with a specific verb and resource: "Sends a new email from one inbox and returns message_id and thread_id." It differentiates itself from reply and draft tools by naming them as alternatives, so an agent can tell this is for newly composed outgoing mail, not replies or drafts.

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 guidance with direct alternatives: "To answer an existing message use post_agentmail_inbox_message_reply; to write without sending, post_agentmail_inbox_draft." It also instructs checking get_agentmail_inbox before sending due to shared account ownership. Nothing is left to inference.

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