Send Email Batch

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

Annotations already declare this is a non-read-only, open-world operation, and the description adds a useful confirmation gate. However, it says nothing about what happens on partial failure across up to 100 messages, nor about the Idempotency-Key replay/409 behavior that the schema exposes -- the two things an agent most needs to know before firing a batch send. No contradiction with annotations.

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 sentences, front-loaded with the core action, then constraints. No filler, though the attachment sentence could be tightened slightly and the confirmation rule might read better before the attachment advice.

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?

An output schema exists so return values need not be described, and the schema itself documents limits (100 messages, 50 recipients, 10 attachments). Still, for a high-stakes open-world batch mutation the description omits batch-level semantics such as atomicity/partial failure and rate or size ceilings, leaving gaps an agent cannot close from annotations alone.

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%, so the baseline is 3, and the description earns an extra point by adding a genuine preference beyond the schema: use uploaded attachment_id refs and avoid inline base64 except for tiny generated content. That is decision-relevant guidance the anyOf in the schema does not convey.

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 and resource with scope: 'send multiple outbound emails in one request'. The batch nature distinguishes it in spirit from sending_send_email / mailbox_send_message, but the description never names the single-send sibling, so the differentiation is implicit rather than explicit.

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 clear precondition ('only when the user confirms every recipient and message') and attachment-routing guidance (prefer attachment_id over inline base64). It does not state when to fall back to the single-message send tool, which is the most likely alternative an agent would weigh.

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