Send mail

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

Beyond the annotations (non-read-only, non-idempotent, destructive), the description discloses critical behavior: no undo or confirmation step, no returned message id, a copy in Sent Items unless saveToSentItems is false, and a specific permission requirement. This goes well beyond what the annotations alone convey and gives the agent a realistic model of the operation's consequences.

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 four sentences, front-loads the core behavior first, and then adds the most decision-relevant caveats (no undo, no id, Sent Items behavior, permission). Every sentence earns its place; there is no filler or repetition of schema content.

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 send-message tool with no output schema, the description covers the operational essentials: side effects, failure-relevant behavior, permission requirements, and an explicit sibling alternative. The input schema handles parameter details, and the annotations handle the low-level safety profile, so nothing an agent needs to call this tool correctly 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 description coverage is 100%, so the input schema fully documents every parameter. The description adds only modest semantic color, such as the saveToSentItems behavior and the overall emphasis on confirming recipients, but it does not materially extend the schema's parameter explanations. 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?

The description states a specific action and resource: 'Sends a message immediately from the signed-in mailbox.' It also distinguishes itself from the sibling mail_create_draft by noting that a send returns no message id and that creating a draft is the alternative. This makes the tool's purpose unambiguous and clearly differentiated.

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 explicitly tells the agent when to use this tool and when not to: confirm recipients and text because there is no undo, and use mail_create_draft when a message id is needed. It also warns about the separate Mail.Send permission requirement, giving practical usage context beyond a simple 'send a message' statement.

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