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

With no annotations, the description carries the full burden. It discloses key behavioral traits: the email sends as the mailbox owner only ('Sends as the mailbox owner and nobody else'), the message is plain text only, and user confirmation is required before sending. These are consequential and actionable details. It doesn't mention auth requirements or error behavior, but the most critical traits are covered.

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 short, purposeful sentences: the action, the identity constraint, the format constraint, and a required pre-call instruction. It is front-loaded with the main purpose and every sentence earns its place without 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 send tool with 6 parameters, no output schema, and no annotations, the description covers the critical behavioral requirements: sender identity, plain text limitation, and user confirmation. It doesn't explicitly mention whether attachments are supported or what happens after sending, but the description is largely sufficient for correct invocation.

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% (to, body, mailbox are documented; cc, bcc, subject are not). The description adds context by stating 'Plain text only,' which reinforces the body format, and 'Sends as the mailbox owner,' which explains the sender identity tied to the mailbox parameter. However, it does not add meaning for cc/bcc/subject, so it only partially compensates for the schema gaps.

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 verb and resource: 'Send a new email from this mailbox.' The word 'new' distinguishes it from reply tools like send_outlook_reply, and 'from this mailbox' anchors the operation to a specific mailbox. This clearly differentiates it from related sibling tools.

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 provides no guidance on when to choose this tool over send_gmail_message, send_outlook_reply, or create_outlook_draft. The only usage-related instruction is 'Ask the user to confirm before calling this,' which is a safety directive, not a selection criterion. No when-not-to-use or alternative routing is mentioned.

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