smtp_reply_message

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

No annotations are provided, so the description must disclose behavioral traits. It explains that the tool fetches the original message via IMAP to construct proper reply headers (In-Reply-To, References, Re: Subject), which is a meaningful behavioral detail beyond a simple 'sends a reply.' However, it does not cover error cases, side effects of sending, or whether the operation is safe or reversible. Given the disclosure of the threading implementation, this is above the baseline of 3 but not a full 5 because it omits potential pitfalls (e.g., failure if original not found, sending failure).

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 a single, information-dense sentence that leads with the action and immediately adds the key threading detail. There is no fluff or redundancy. Every word contributes to clarifying the tool's purpose and distinguishing it from alternatives.

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?

Given the tool's complexity (7 parameters, nested attachment object, output schema present), the description is largely complete: it defines the purpose and key behavior. However, it does not explicitly address sibling selection (e.g., 'use this instead of smtp_send_message when replying') or mention dependencies like IMAP availability. The schema fills parameter details, but the description could better position the tool among the 31 siblings. It is complete enough for a competent agent but leaves some room for clearer guidance.

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 all seven parameters (message_id, body_text, body_html, reply_all, account_id, attachments, include_original_attachments) are already documented with their meanings and defaults. The description adds context about the threading behavior but does not enhance the understanding of any specific parameter. Since the schema carries the weight, a baseline score of 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 verb ('Reply') and resource ('an existing message via SMTP'), and adds a concrete differentiator ('fetches original for proper threading'). This clearly distinguishes it from smtp_send_message (new message) and smtp_forward_message (forwarding), leaving no ambiguity about what the tool does.

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 implies when to use it (to reply to an existing message) but does not explicitly contrast it with alternatives like smtp_send_message or smtp_forward_message. There is no 'use this instead of...' guidance, nor mention of prerequisites such as the original message being accessible via IMAP. Usage is clear from the name and phrasing, but the description does not actively route the agent away from siblings.

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