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

Annotations already flag destructiveHint=true and openWorldHint=true, so the safety profile is partly covered. The description adds real value beyond that: it discloses the plain-text-only constraint, warns against HTML markup, and mandates user confirmation before sending — none of which the annotations convey.

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?

Three short clauses, front-loaded with the action, then the format constraint, then the confirmation gate. No filler and nothing buried.

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 six-parameter outbound send with no output schema, the description covers the essentials an agent needs: sending identity, plain-text format, and the confirmation requirement. It leaves cc/bcc handling and any recipient-count limits unaddressed, which is a minor gap given the schema's enum-less, mostly self-describing 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 50%, and the description only reinforces the body format ('plain text only, real line breaks') already noted in the body schema and clarifies the mailbox-as-sender-identity relationship. It says nothing about cc, bcc, or subject beyond what the schema minimally provides.

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 (Send) plus resource (new email) and scoping (from this AgentMail inbox, as that inbox's address). The word 'new' implicitly separates it from send_agentmail_reply and create_agentmail_draft, and the sending-identity clause pins down what the mailbox parameter represents.

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 a concrete usage directive — 'Ask the user to confirm before calling this' — which tells the agent this is a gated action. It doesn't explicitly name send_agentmail_reply or create_agentmail_draft as alternatives for other cases, so the routing is implied rather than spelled out.

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